Neurogenesis: The Journal of Undergraduate Neuroscience - Fall 2011

Volume 1 Issue 1 Fall 2011

Copyright Š 2011 Financial support provided by The Bassett Fund

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Editorial Board Editor-in-Chief Lily Pham Class of 2012 lily.pham@duke.edu

Publishing Editor Kathryne Wood Class of 2012 katy.wood@duke.edu

Managing Editors Rory Lubner Class of 2013 rory.lubner@duke.edu

Kelly Ryan Murphy Class of 2013 kelly.murphy@duke.edu

Associate Editors Christine Lee Class of 2014 christine.lee@duke.edu Biqi Zhang Class of 2014 biqi.zhang@duke.edu

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Faculty Advisors Leonard White, Ph.D. Associate Professor Duke University School of Medicine Director of Education Duke Institute for Brain Sciences len.white@duke.edu Craig Roberts, Ph.D. Assistant Director of Education Duke Institute for Brain Sciences craig.roberts@duke.edu Ann Motten, Ph.D. Department of Chemistry ann.motten@duke.edu

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Letter from the Editor Welcome to the inaugural issue of Neurogenesis!

The idea for our journal was born three years ago when the whispered rumors of a neuroscience major manifested itself into reality. Our founding group of students, including some amazing Class of 2011 alumni, worked tirelessly to elucidate the mission of Neurogenesis. In our often lengthy and heated debates we negotiated every detail from our name to the reach of the final product beyond our own Duke University. One detail that our members unanimously agreed upon was the scope of the journal, recognizing the truly unique interdisciplinary nature of neuroscience. At its core, neuroscience is the study of the human brain and mind, a study to unravel the biological and philosophical mysteries of the human condition. We saw Neurogenesis as an opportunity to showcase the extraordinary work of undergraduates in answering the fundamental questions through the perspective of philosophy to neurobiology.

Our first issue is exemplary of the breadth and depth of the work done by students at Duke. This issue features original research in both cognitive neuroscience and neurobiology, a discussion of free will, of consciousness, and of ethics and deception. Beyond illuminating each author’s valuable insight on the topic, we hope that these articles will serve as a catalyst for discussion between you and your peers. Most of all, we hope that through these works, you will perhaps be inspired to voice your opinions on issues in neuroscience.

A special thank you goes to our alumni, Rolando Rengifo and Austin Mattox. Their input and guidance set our ideas in motion, leading us to where we are today. Finally, I would like to take this opportunity to thank my incredibly hard-working editorial staff who made this publication possible.

Without further ado, I hope you enjoy this very first edition of Neurogenesis: The Journal of Undergraduate Neuroscience.

Sincerely,

Lily Pham Editor-in-Chief Vol 1 Issue 1 | Fall 2011 | neurogenesisjournal.com | iii

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Table of Contents 2

The cognitive neuroscience of deception: Advances in neuroscience, criminal law, and ethics Rolando Rengifo

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Neuroscience on the nature of consciousness

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Free will: Not worth giving up on

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Effects of resting state on perceptual skill learning

Hannah Gold

Ryan Bartholomew

Snighda Peddireddy

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Temporal and spatial constraints of the cross-modal spread of attention Helen Zhang

40

F eature

A rticles

Neuroscience research opportunities at Duke Rory Lubner & Kelly Murphy

7

Resolving the schizophrenia paradox

13

Link between brain reward pathways and sodium appetite: Regulation of DARP-32 in response to sodium deficiency

Caitlinn Finn

Sarah Hochendoner

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The Cognitive Neuroscience of Deception: Advances in Neuroscience, Criminal Law Applications and Ethics Rolando Rengifo1 Duke University, Durham, North Carolina 27708 Correspondence should be addressed to Rolando Rengifo (rolando.rengifo@duke.edu) 1

ABSTRACT: Neuroscientific advances promise to change the way the law and the legal system are viewed. In this paper, neuroimaging technology is discussed in terms of its development and how it has improved understanding of deception pathways. As knowledge builds, mistaken convictions that lead to wrongful punishment of innocent parties could be avoided. Likewise, the release of dangerous criminals back into society could also be prevented. In addition, ethical issues (i.e. premature adoption, misapplication through misunderstanding of technology and privacy concerns) that currently prevent the implementation of mind reading or deception detection technology in the courtroom are discussed. Limitations of such technology are also discussed along with advances and future directions in research. Finally, a pathway is proposed that could explain the origins of the mechanism of deception and how it could be tested.

Introduction Criminal law is a field of growing interest in the world of neuroscience because of its recent technical advancements. Research suggests the possibility of more precise sentencing through, among other things, mind reading and deception detection. Methods such as functional Magnetic Resonance Imaging (fMRI), Positron Emission Tomography (PET), the P300 memory reading method and the Concealed Information Test (CIT) have been suggested to be appropriate tools in the attempt to undercover previously inaccessible evidence within the brain of the individual being prosecuted. However, there are a number of issues to be addressed in considering this as a possible way of obtaining evidence: relevance of evidence, accuracy of techniques, the idea of ‘cognitive privacy’, etc.

Given the wide scope of literature in the topic, this paper will focus on the relevance of evidence and how the new evidence may affect a jury in making a conviction with the use of neuroscientific babble and ‘expert witnesses’. Additionally, ethical concerns must be addressed to provide context to the problems that integrating this new technology in a court of law might bring. For the sake of simplicity, the focus of this paper will be on the potential use of neuroscientific evidence by the prosecution in criminal trial to provide background to the neuroscientific evidence of interest.

At this time, the probative value of neuroscientific evidence in the courtroom is still under scrutiny. In particular, the use of neuroimages has been suggested as admissible evidence for criminal cases by the prosecution to determine pathologies that might be signatures of antisocial or criminal behavior with little success (Sinnott-Armstrong et al., 2008). Given the magnitude of literature surrounding this field of study, we simply mention the research but it will not be discussed further. Similarly, it has been suggested that neuroscientific evidence could be used to pinpoint neurological pathways associated with decep2 | neurogenesisjournal.com | Fall 2011 | Vol 1 Issue 1

tion—the research on which this paper will focus (Abe et al., 2007; Abe 2009; Abe 2011; Langleben et al., 2005).

This field of research is not new, as it follows from previous attempts to detect deception through the use of polygraphs or other scientific tools for measuring arousal (Wolpe et al., 2005; Abe, 2011). The use of polygraphs has been deemed to be unreliable by the scientific community, but application of new technology has not yet been tested with subjects on trial because of several ethical issues that must be defined. Regardless, there is a growing body of research suggesting that implementation of neuroscience evidence in this regard would be beneficial to the law system, adding a degree of efficiency in criminal sentencing.

Pertinent evidence suggesting advances in technological research has been reported, shining new light on answering the question of relevance of neuroscientific evidence applied to deception detection.

Deception and the Brain – In Search of a Pathway Deception is a psychological process by which one individual deliberately attempts to convince another person to accept what the liar knows to be false—typically in favor of the liar or sometimes others—to maximize gain of a given benefit or to avoid loss (Abe, 2011; Abe, 2009; Lefebvre at al., 2009; Abe et al., 2007). Among the many activities and situations in which deception is covered— white lies, jokes, disguise, forgery, magic, financial fraud and scams, and more—there exists a need to recognize different genres of deception and how these are shaped by the brain and mapped in the brain (Abe, 2011). While some lies may lead to serious consequences—either positive or negative—because of their selfish and antisocial premise, others may lead to smoother communication and overall self-fulfillment because of their altruistic and pro-social foundation (Abe, 2011; Abe, 2009).

Over the years the study of deception has captured increased attention among psychologists and neuroscien-

Review tists. Not surprisingly, lie detection has become the most popular area of research because of the useful implications of such methodologies in the courtroom, classroom and clinical setting, among others. In terms of human behavior, some non-verbal cues have been found to be directly associated with lying such as changes in physical expression, pitch of voice and body posture (Abe, 2011; Frank & Ekman, 1997). Lie-detection systems, such as the polygraph, have been suggested in the past as appropriate methods of deception detection as they measure a subject’s physiologic responses by monitoring chest expansion, pulse, blood pressure, and electrical conductance of the skin—all aspects which are often physiologically amplified when someone is lying (Abe, 2011; Wolpe et al., 2005). However, there are a number of limitations to this method. The main problem is that the polygraph assesses activity of the autonomic nervous system, so signal changes may reflect not only arousal during deception but general anxiety regardless of the cause (Wolpe et al., 2005).

Another method that has been suggested is the use of event-related potential (ERP) (Lefebvre et al., 2009; Cutmore et al., 2009; Mertens & Allen, 2008). This method focuses on the use of brain responses in lie detection, but like the polygraph it has not been assessed to be entirely reliable. Regardless, these systems provide preliminary insight into the psychological processes associated with various aspects of deception (Abe, 2011).

Pioneering work by Spence et al. (2001) led to an increase in the number of neuroimaging studies that have resulted in a better understanding of the brain regions associated with deception. Through these neuroimaging studies, it was found that the prefrontal cortex plays a role in deception, though the precise role of this region and other subregions of this area are still unclear (Abe et al., 2007; Phan et al., 2005). It has further been posited that the anterior cingulate cortex is involved in the inhibition of true responses and the production of deceptive responses (Abe et al., 2006; Nunez et al., 2005). Also, activity in the amygdala has been reported as crucial for emotional processing and is thus reportedly seen in relation to deceptive intention (Abe et al., 2007). Nonetheless, the neural mechanisms that lead to activity in the prefrontal cortex subregions are still under investigation. Given that the mental activity associated with deception is complex, developing a better idea of what these mechanisms are will continue to be a difficult task. One of the obstacles is being able to differentiate between the process involved in developing a deceptive idea and isolating that mechanism from the neural activity associated with the intention of deceiving—deception with social intentions (Abe, 2011; Abe et al., 2007). It should be noted that, in relation to deception, the dorsolateral prefrontal cortex is associated with executive function and the ventromedial prefrontal cortex with emotional regulation of social interaction (Abe et al., 2007). In the following sections, empirical evidence will be discussed that has led researchers to suggest the possibility that such neuroimaging should be tested in a real

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courtroom setting because of its promising efficiency and relative accuracy.

The application of neuroimaging to understand deception has been developed in what is now known as cognitive neuroscience of deception (Abe et al., 2007; Davatzikos et al., 2005). There are multiple laboratory groups around the world that devote their research to understanding the complex neural system that makes deception possible in primates. Humans’ evolutionary development of deception still puzzles social evolutionary scientists. The rest of the report will focus on human studies for the sake of brevity and topic relevance.

Abe et al. (2007) reported a positron emission tomography (PET) study trying to dissociate the development of a deceptive idea and the associated neural signaling from the intention of deceiving and the relevant neural connection to the subregions of the prefrontal cortex. Abe et al. hypothesized that the development of a deceptive idea would be associated with the lateral prefrontal cortex while the intention associated with the deception would show higher activity at the medial prefrontal cortex. Results emphasize a critical aspect of human deceptive behavior: it “provides clear evidence that at least two factors essential for human deception are supported by distinct subregions within the prefrontal cortex” (Abe et al., 2007). Since then, similar results have been obtained in the Abe laboratory using other neuroimaging methods such as fMRI (Abe, 2011; Abe, 2009).

Langleben et al. (2005) reported the first quantitative estimate of the accuracy of fMRI in conjunction with a formal forced-choice paradigm in detecting deception in individual subjects. The paradigm aimed to balance the salience of target cues to elicit deceptive and truthful responses. Accuracy was determined for this model in the classification of a single lie and truth event. As reported later by Abe, Langleben found that the net activation associated with lie production was observed in the superior medial and inferolateral prefrontal cortices. Reportedly “lie was discriminated from truth on a single-event level with an accuracy of 78% . . . [results suggest that] fMRI, in conjunction with a carefully controlled query procedure, could be used to detect deception in individual subjects” (Langleben et al., 2005).

Regardless of all the advances that technology has brought to the field of cognitive neuroscience of deception, there is still more to learn and define before real world applications of suggested methodology can be implemented.

It appears that the proposed region association suggested

by Abe et al. (2007) has promise, but his future publications show no significant advances in getting closer to answering the mechanism question. In a paper published in 2011, Abe states that functional neuroimaging conducted in healthy subjects does not provide direct evidence that a certain brain region is necessary for a specific cognitive process. There is a baseline error that must always be accounted for and, based on the circumstances, there might also be further activation error due to the unusual or unexVol 1 Issue 1 | Fall 2011 | neurogenesisjournal.com | 3

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pected conditions a test subject might be in. Furthermore, it should be noted that there is a line that must be drawn when comparing experimental subject scenarios to real life scenarios, due to experimental limitations that would not be factored in during real life trials (i.e., motivation of the subject to lie, motivation of the subject to be present at the study, etc.). However, the relevance of empirical evidence should be questioned in par with data obtained for analyses in other fields—there is no reason to believe that deception data will be less helpful than other empirical data thus acquired. One must be careful when comparing group to single individual data. In order to fully understand the question of how cognitive and neural correlates of deception are related with other processes researchers have to look at group and individual experimental data and show significant differences between experimental conditions and group data. Furthermore, care must be taken when studying individual neuroimaging data of complex cognitive processes—such as deception—in individuals between single trials. These comparisons are particularly challenging because of the low signal-to-noise ratio in such trials (Ganis, 2009).

Even though research in the field of cognitive neuroscience of deception has been growing tremendously in the past few years there is still much work to do. However, at this point in time, findings suggest that neuroimaging studies are not at a point to provide significant evidence to be relevant in a court of law. But, how can relevance be defined?

Relevance of Neuroimaging as Evidence in a Court of Law According to the Federal Rules of Evidence (SinnottArmstrong et al., 2008), courts follow the following definitions of relevance: FRE 401: “relevant evidence” means evidence having any tendency to make the existence of any fact that is of consequence to the determination of the action more probable or less probable than it would be without the evidence.

FRE 402: All relevant evidence is admissible, except as otherwise provided by the constitution of the United States, by Act of Congress, by these rules, or by other rules prescribed by the Supreme Court pursuant to statutory authority. Evidence which is not relevant is not admissible.

FRE 403: Although relevant, evidence may be excluded if its probative value is substantially outweighed by the danger of unfair prejudice, confusion of the issues, or misleading the jury, or by consideration of undue delay, waste of time, or needless presentation of cumulative evidence.

Reviewing FRE 401, it is explicitly stated that in order for evidence to be deemed relevant it must add to the evidence already in place in a concrete manner. Thus, the existing evidence must gain value and insight from the addition of the suggested new evidence to be considered relevant. Because of this, neuroimaging data should provide 4 | neurogenesisjournal.com | Fall 2011 | Vol 1 Issue 1

Review an accurate report that will make the final decision by the jury easier and more definitive. To be able to discard the variable of deceit would be an incredible feat for neuroscience and a great advancement to criminal prosecution and fact reliability. From this point onward any suggestion of evidence relevance will be presented from the perspective of the prosecution.

FRE 402 and 403 go hand in hand, as both of these rules define evidence admissibility. FRE 403 is particularly important because it brings up important issues that should be considered when thinking about neuroimaging as evidence for pinpointing deceit intentions and actions.

Some of these questions have been described before but will be presented again (Sinnott-Armstrong et al., 2008): (1) Should neuroimaging evidence be admitted in trial?; (2) What is the probative value neuroimaging evidence would provide in relation to deception detection?; (3) Is there a danger of the prosecution biasing the jury with the use of neuroimaging data? Could the prosecution use such evidence in a way that is misleading or confusing to the jury?; and (4) If so, does the danger outweigh the probative value of such evidence?

Answers to these questions have not been pursued, in terms of neuroimaging application to combat deceit in the courtroom—partly because the opportunity has not presented itself to suggest such evidence as admissible in court to date. Even though mock scenarios have been studied and other researchers have tried to determine the accuracy of such applications (Langleben et al., 2005; Lui & Rosenfeld, 2008; Winograd & Rosenfeld, 2011) in depth analyses of these questions in this context are yet to be produced. This study proposes some potential answers from analysis of the literature.

The first question is directly related to the topic of relevance and can simply be answered with FRE 402 and FRE 403. If the criteria are met then the evidence should be presented. From the perspective of the prosecution this would help in determining whether the defense has hidden information that the defense is reluctant to reveal or—if permitted after an ethical review—whether the defense has a hidden agenda or outside sources that might be illegally aiding their client. The second question tries to define the probative value of neuroimaging evidence in deception detection. It makes intuitive sense to assume that removing the variable of deception would add significant value to the evidence and stated facts in a court of law. Thus, from a purely intuitive perspective the probative value of including neuroimaging evidence in deception detection is very high. Is the evidence dangerous? To answer this question, the study conducted by Langleben et al., (2005) where 78% accuracy in detecting lies was found must be considered. The result is well above chance, but one must consider that even if ~80% of individuals were convicted without reasonable doubt, there would be ~20% who may be telling the truth but are detected as lying or vice versa. This means ~20 individuals out of 100 put on trial would be unjustly sentenced or not sentenced when

Review they should have been. The number is ludicrous when not considered as a mere percentage and thought of in terms of individuals. From the perspective of the prosecution, in a perfect world where the prosecution was not challenged, the percentage would assure them the majority of case advantages simply by presenting an expert witness detailing the ‘facts’ of neuroscience. However, the use of neuroscientific babble by the expert witness might suggestively tarnish the jury’s bias and they might make up their mind before the end of the trial. Thus, there are dangers that must be considered. However, the dangers seem to fall short in relation to removing the deceit variable from trial in a court of law. Even though empirical congruency must yet be found, the benefits may outweigh the dangers of neuroimaging implementation to combat deceptive behavior in the courtroom.

Ethical Concerns: An Introduction Ethical concerns in relation to lie-detection methods have been presented and have been studied in depth over the past few years. Due to the current state and development of neuroimaging and other methods of lie-detection the key concerns that have surfaced should be discussed (Wolpe et al., 2005): (1) premature adoption; (2) misapplication through misunderstanding of technology; and (3) privacy concerns.

Premature adoption has become an imminent threat because of the pressure put on research organizations by the federal government, which provides most of the research funding. In particular, the defense-related security agencies are seeking to get the new technology out as soon as possible. Even though such security promise might be desirable, the consequences could be dire if not enough testing is done to make sure the technology is at the level it should be. Furthermore, competition is thus heightened among research groups and thorough analysis is sometime sacrificed in order to gain funding. Quality of results should not be regarded as inessential, for a good foundation is the basis of a successful tomorrow.

Misunderstanding technology can also lead to problems both in results analysis and application in the courtroom.

Wolpe et al. (2005) states: “none of the new imaging technologies actually detect “lies.” By this statement, Wolpe means that there are a number of physiological processes that lead to ‘signal activation’ that is seen in neurological data presented by P300 electrophysiology, fMRI images or PET scans. The main challenge, Wolpe claims, is the “separation of a deception-related signal from the host of potentially confounding signals . . .” (Wolpe et al., 2005). As presented earlier in this paper, it appears that such a separation was empirically supported in the prefrontal cortex (Langleben et al., 2005; Abe et al., 2007; Abe, 2009; Abe, 2011). Regardless, mechanisms are yet to be suggested as research continues to understand differentiations between baseline signals and those associated with deception. Until these mechanisms are better defined a lack of understanding of the technology and its applications will continue to

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hinder progress.

Finally, privacy is an issue that much literature has noted as a major source of concern before such methodology can be used to assess individuals on trial (Wolpe et al., 2005; Abe et al., 2007; Abe, 2011; Winograd, 2011). At present, privacy in the courtroom has been defined by constitutional law as a the inherent right to privacy that protects the liberty of people to make certain crucial decisions regarding their well being without government coercion, intimidation, or interference. Moreover, the government is not constitutionally permitted to regulate deeply personal matters. By this definition one would have to assume that intimate thoughts are a deeply personal matter and thus, the government has no right to regulate or make these thoughts public. In order for neuroimaging evidence to be considered appropriate, the definition of privacy in the courtroom would have to be redefined. Does an individual have the right to keep his or her subjective thoughts private? This would be the first question that would have to be addressed in defining cognitive privacy. The ethical issue at hand is what may keep deception detection methods from entering the courtroom as an aid in assessing individuals on trial in the near future.

Conclusions From a scientific perspective, there appear to be specific subregions of the prefrontal cortex that are activated during deception. The development of a deceptive idea appears to be associated with the lateral prefrontal cortex while the intention associated with the deception seems to be associated with the medial prefrontal cortex. The fact that these regions have been determined is a step in the right direction for pinpointing the exact mechanism by which deception originates. However, there is still much ground to cover as researchers seek to define the fine line between brain activity—related to preparing a lie and deceiving— from brain signaling associated with other physiological functions. Given the mechanistic complexity of deception it will be some time before a pathway can be defined with more certainty. Even though other brain areas such as the ACC and amygdala have been suggested to be involved in the pathway, a precise association has not been made. One potential mechanism could be a loop association between the dorsolateral PFC and the ventromedial PFC with somatosensory associations that will eventually define the baseline of the deception pathway. Since it has been established that (1) the dorsolateral PFC is associated with executive function and (2) the ventromedial PFC is associated with emotional regulation of social interaction, it could be posited that an emotional trigger first determines the intention of deceiving which is followed immediately by conscious executive control—inhibition of the truth— that eventually leads to the act of stating a lie. Experiments to test this hypothesis would have to consider confounding variables that may also affect brain signaling during experimental trials. Identifying these variables would be the major challenge. The scenario would more accurately Vol 1 Issue 1 | Fall 2011 | neurogenesisjournal.com | 5

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be portrayed in a real life simulation so that motivation is not lacking. Given the technological advances in virtual simulation, this test would be feasible and something for researchers to explore.

Advances in neuroscience are also affecting the way law is portrayed. For the first time, neuroscience research has made it possible to examine the human brain—the ‘seat’ of consciousness, decision making, thought, memory and personality (Aronson, 2010). Some scientists suggest that neuroscience will eventually change the law and our legal system. Here, for example, the idea that use of deception detection techniques in the courtroom would necessitate redefining privacy has been considered. Since the increasing neuroscientific literature covers a much larger scope than deception detection, the ways in which new evidence will affect our understanding of responsibility (SinnottArmstrong, et al., 2008) and free will (Greene and Cohen, 2004) should also be explored. There are some, however, who argue against the admittance of brain related evidence, stating that such evidence does not change the fact that people--not brains--commit the crimes. In light of such arguments, it is nonetheless clear that additional advancements in neuroscience will be necessary if indeed the field is to influence the legal system, as some researchers expect it will. It is not far fetched to imagine that neuroscience will enter the courtroom in many ways and forms in the future.

What about the ethical limitations in implementing deception detection or mind-reading techniques in the courtroom? These issues are at the core of the problem of introducing neuroscientific data in the courtroom. Proposed probabilities regarding lie detection have been presented from the study by Langleben et al. (2005). However, when dealing with a human life, one cannot be nonchalant about error probabilities. Is it ethical to convict an individual without hard, definitive evidence? As technology progresses and understanding of deception mechanisms advances, hopefully, the goal of reaching definitive convictions will be accomplished.

Abe, N., et al. (2007). “Deceiving Others: Distinct Neural Responses of the Prefrontal Cortex and Amygdala in Simple Fabrication and Deception with Social Interactions”. Journal of Cognitive Neuroscience 19(2): 287295.

Abe, N. (2009). “The neurobiology of deception: evidence from neuroimaging and loss-of-function studies.” Current Opinion in Neurology 22(6): 594-600.

Abe, N. (2011). “How the Brain Shapes Deception: An Integrated Review of the Literature”. The Neuroscientist. Retrieved from: http://nro.sagepub. com/content/early/2011/03/29/1073858410393359 Ambach, W., S. Bursch, et al. (2010). “A Concealed Information Test with multimodal measurement.” International Journal of Psychophysiology 75(3): 258-267.

Aronson J.D., 2010. “The Law’s Use of Brain Evidence”. Annu Rev Law Soc Sci 6: 93-108.

Cierpka, M., M. Luck, et al. (2007). “On the ontogenesis of aggressive behaviour.” Psychotherapeut 52(2): 87-101.

Cutmore, T. R. H., T. Djakovic, et al. (2009). “An object cue is more effective than a word in ERP-based detection of deception.” International Journal of Psychophysiology 71(3): 185-192.

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Review Davatzikos, C., et al., 2005. “Classifying spatial patterns of brain activity with machine learning methods: Application to lie detection”. Neuroimage 28: 663-668.

Frank, M.G. and Ekman, P. 1997. “The ability to detect deceit generalizes across different types of high-stake likes”. J Pers Soc Psychol 72: 14291439.

Glenn, A. L. and A. Raine (2009). “Psychopathy and instrumental aggression: Evolutionary, neurobiological, and legal perspectives.” Int J Law Psychiatry 32(4): 253-258.

Green, J. and J. Cohen (2004). “For the Law, Nuroscience Changes Nothing and Everything”. Philosophical Transactions of the Royal Society B 359: 1775-1785.

Langleben, D.D., et al., 2005. “Telling Truth From Lie in Individual Subjects With Fast Event-Related fMRI”. Human Brain Mapping 26: 262-272.

Lefebvre, C. D., Y. Marchand, et al. (2009). “Use of event-related brain potentials (ERPs) to assess eyewitness accuracy and deception.” International Journal of Psychophysiology 73(3): 218-225.

Lui, M. and J. P. Rosenfeld (2009). “The application of subliminal priming in lie detection: Scenario for identification of members of a terrorist ring.”

Psychophysiology 46(4): 889-903.

Mendez, M. F. (2006). “What frontotemporal dementia reveals about the neurobiological basis of morality.” Medical Hypotheses 67(2): 411-418.

Mertens, R. and Allen, J.J.B. 2008. “The role of psychophysiology in forensic assessments: Deception detection, ERPs, and virtual reality mock crime scenarios”. Psychophysiology 45: 286-298.

Muller, J. L. (2006). “The impact of neuro-biological factors in the genesis of violence II - neuro-anatomical and neuro-functinal aspects.” Nervenheilkunde 25(11): 962-967.

Muller, J. L. (2009). “Forensic psychiatry in the era of neuroscience. Present status and outlook for neurobiological research.” Nervenarzt 80(3): 241-+.

Nunez, J.M., et al., 2005. “Intentional false responding shares neural substrates with response conflict and cognitive control”. Neuroimage 25: 267-277.

Patrick, C. J. (2008). “Psychophysiological correlates of aggression and violence: an integrative review.” Philosophical Transactions of the Royal Society B-Biological Sciences 363(1503): 2543-2555.

Phan, K.L., et al. (2005). “Neural correlates of telling lies: A functional magnetic resonance imaging study at 4 Tesla”. Academic Radiology 12: 164172.

Sinnott-Armstrong, W. (2008). “Brain images as legal evidence”. Episteme 5(3): 359-373.

Spence, S.A. et al., 2001. “Behavioral and functional anatomical correlates of deception in humans”. NeuroReport 12: 2849-2853.

Stolpmann, G., P. Fromberger, et al. (2010). “Forensic assessment Are biological facts useful?” Monatsschrift Fur Kriminologie Und Strafrechtsreform 93(4): 300-312.

Winograd, M. R. and J. P. Rosenfeld (2011). “Mock crime application of the Complex Trial Protocol (CTP) P300-based concealed information test.”

Psychophysiology 48(2): 155-161.

Wolpe P.R., (2005). “Emerging Neurotechnologies for Lie Detection”.

American Journal of Bioethics. 5: 39-49.

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Resolving the schizophrenia paradox Caitlin Finn1 Duke University, Durham, North Carolina 27708 Correspondence should be addressed to Caitlin Finn (caitlin.finn@duke.edu) 1

ABSTRACT: Past research has exposed three conflicting pieces of information: (1) schizophrenia is highly heritable; (2) schizophrenia has a constant prevalence of 1% in every culture across the globe; (3) the symptoms of schizophrenia are highly maladaptive, leading to severely reduced fecundity rates. Given its prevalence, heritability, and maladaptive qualities, schizophrenia should have been eliminated from the population by natural selection, yet it remains. Researchers have proposed three main theories associating schizophrenia with adaptive traits in an attempt to explain this paradox. Crow postulates that schizophrenia evolved as a byproduct of the cerebral lateralization necessary for complex language. Another theory suggests the disorder results from faulty development in the regions that compose the social brain. Finally, some propose creativity genes confer an evolutionary advantage on schizotypal individuals but also cause schizophrenia, thereby maintaining the disorder in the population. These theories provide insight into the evolutionary origins of schizophrenia, which may open the door to future research and improved treatment.

Introduction Schizophrenia, perhaps the most devastating psychological disorder, represents a fundamental split from reality. Given the maladaptive qualities of this disorder, it is not surprising that individuals with schizophrenia have low fecundity rates. Schizophrenia has a global prevalence of 1% in the general population, and a higher prevalence in relatives of schizophrenic individuals (McGuffin, Owen, & Farmer, 1995). Furthermore, family, twin, and adoption studies have shown heritability to lie between 63 and 85%, demonstrating a strong genetic basis (McGuffin et al., 1995). Therein lies the paradox of schizophrenia: How can a genetically transmitted disorder as maladaptive as schizophrenia remain at such a high frequency in the global population?

According to the Diagnostic and Statistical Manual of Mental Disorders, Revised 4th ed. (DSM-IV, 2000), two of the following symptoms must be present to merit a diagnosis of schizophrenia: delusions, hallucinations, disorganized speech, grossly disorganized or catatonic behavior, or negative symptoms (American Psychiatric Association, 2000). Schizophrenia can manifest in clusters of positive, negative, and disorganized symptoms. Positive symptoms represent an addition of features, including delusions and hallucinations. Negative symptoms are defined by the absence of normal behavior, such as alogia, avolition, anhedonia, and flat affect. Disorganized systems involve unpredictable and erratic speech, motor functions, and emotions. Combinations of these symptoms cluster into five schizophrenia subtypes: disorganized, paranoid, catatonic, undifferentiated, and residual (DSM-IV, 2000).

Schizophrenia has many genetic and symptomatic correlates with schizotypal and schizoid personality disorder, which are characterized by “odd” or “eccentric” behaviors and unusual perceptions (Rossi & Daneluzzo, 2002; Fisher, Mohanty, Herrington, Koven, Miller, & Heller, 2004).

Genetic evidence strongly suggests that schizophrenia lies on a continuum of psychosis that includes varying levels of

schizotypal personality.

It is possible that somewhere on the continuum of disorder lies an evolutionary advantage, allowing the harmful dysfunction to remain in the population. Darwin’s theory of natural selection proposes that the fittest individuals in a population will survive to pass on their adaptive traits in the form of their genes, while less adaptive traits are eliminated through less reproductive individuals (Darwin, 1859). Therefore, a population will become more fit over time, though harmful genotypes can arise through mutation. In mutation-selection balance, the mutation rate balances the rate natural selection is able to remove the harmful mutation from the population. A mutation in a particularly vulnerable “upstream” gene, which controls the expression of many other “downstream” genes, disrupts the expression of many traits. Therefore, a few mutations can have a large cumulative effect (Keller & Miller, 2006).

There are several ways harmful genes can be actively maintained at high levels in the population, despite the forces selecting against them. First, there can be a heterozygote advantage, as in the case of sickle cell anemia, whereby carriers of the gene have an advantage over noncarriers (Keller & Miller, 2006). Second, a harmful gene can be selected through antagonistic pleiotropy, which occurs when a gene coding for a harmful trait is also responsible for a beneficial trait. In this case, the gene can remain in the population if its benefits outweigh its costs (Keller & Miller, 2006). Finally, a harmful gene can be selected through frequency-dependent selection if the gene is beneficial only when possessed by a small percent of the population (Keller & Miller, 2006). An adaptationist approach that examines schizophrenia as a consequence of other adaptations can provide crucial insight into the nature of the disorder. Empirical and theoretical research has shown that schizophrenia may have evolved as an evolutionary byproduct of other traits, such as language, sociality, and creativity. This paper will review the evolutionary and neurological relationship between schizophrenia and Vol 1 Issue 1 | Fall 2011 | neurogenesisjournal.com | 7

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language, the social brain, and creativity in an effort to explain its underlying evolutionary causes.

Language Complex language, characterized by an intricate system of syntax and semantics, is a fundamental part of all human societies. Similarly, schizophrenia is a universal disorder despite drastically different environments (McGuffin et al., 1995). The ubiquity of both language and schizophrenia suggest their genetic basis evolved prior to man’s exodus from Africa around 150,000 years ago. In fact, schizophrenia has been found in the aboriginal Australian population, which has been separated from the rest of the human population for 50,000 years (Crow, 2000).

The genetic changes that occurred slightly before humans’ mass dispersal across the globe could account for Homo sapiens’s great reproductive success. Many scientists believe the strongest candidates for this change are the characteristics that separate humans from other species, namely language, intelligence, or complex social interactions.

Crow (1997) proposes a genetic event, specifically cerebral lateralization, allowed humans to inhabit new ecological niches and is responsible for the development of both language and schizophrenia.

Crow argues that brain lateralization appeared suddenly as a result of a genetic mutation, which caused a speciation event that allowed humans to form a new branch of the evolutionary tree. The relatively separate development of each hemisphere enables control of specific functions to be localized in different areas, allocating more brain space for each function. Crow also proposes the lateralization gene is homologous on both the X- and Y-chromosomes, which causes sex-dependent trait expression (Crow, 1997).

Sex-dependent expression of lateralization would allow females to select males who best displayed the attractive trait, thereby increasing the speed of the speciation event.

Crow derives support for this argument from the effects of various aneuploid disorders. Individuals who lack an Xchromosome, as in Turner’s syndrome (XO), have righthemisphere spatial problems, while those with an extra X-chromosome, as in Klinefelter’s (XXY) and triple X syndromes (XXX), have left-hemisphere language deficits (Crow, 1997). A sex-linked lateralization gene may explain the sex differences in both language and the development of schizophrenia.

Brain lateralization is intricately tied to the production of complex language, which primarily resides in the left hemisphere. This language-related hemispheric asymmetry can be seen in anatomical studies. For example, the planum temporale, a vital part of language comprehension, is larger in the left hemisphere (Breedlove, Watson, & Rosenzweig, 2010). The spatial aspects of language are located in the right hemisphere, and the temporal aspects are located in the left hemisphere (Breedlove et al., 2010).

Communication between hemispheres and hemispheric dominance are also essential in other modalities, such as motor control. For example, the necessity of hemispheric 8 | neurogenesisjournal.com | Fall 2011 | Vol 1 Issue 1

Letters dominance can be seen in human handedness, a genetically transmitted indicator of lateralization. Individuals with a moderate hand preference are at an advantage to those with the strongest preference, in terms of some cognitive abilities including coordination of language, while ambidextrous children are at the largest disadvantage (Crow, 1997). This example provides evidence for a heterozygote advantage in lateralization.

Crow hypothesizes a lack of hemispheric lateralization could account for the core positive symptoms of schizophrenia (Crow, 2000). Many schizophrenic patients present bizarre experiences regarding their thoughts, such as broadcasting or insertion by a foreign agency. Incomplete hemispheric dominance could cause the left hemisphere to perceive the right hemisphere’s thoughts as coming from an external source (thought insertion). Furthermore, an inability to distinguish between thought and speech could result in the perception of thoughts as spoken aloud or broadcasted (Crow, 2000). In addition, auditory hallucinations, a classic positive symptom of schizophrenia, may be a result of the left hemisphere perceiving signals from the right hemisphere as external speech, thereby creating the illusion of one’s thoughts coming from “voices” (Crow, 2000). These universal, core symptoms may be the result of a lack of distinction between thought and speech produced by hemispheric symmetry.

There are several weaknesses in Crow’s argument. A failure of lateralization may explain schizophrenia’s positive symptoms, but it fails to explain negative and disorganized symptoms, such as flat affect, catatonia, and anhedonia. Language impairment does not always accompany schizophrenia. Additionally, Crow’s assumption that language evolved rapidly during a speciation event is contentious. Research has shown that language evolved slowly, and some primate species show slight lateralization (Brüne, 2004; Burns, 2004). Furthermore, Crow’s argument implies that humans are the only species with psychosis, an assumption that lacks support. However, in spite of the weaknesses in his argument, behavioral, functional imaging, and genetic studies support Crow’s theory.

Behavioral research has provided evidence for the involvement of atypical lateralization in schizophrenia. Asai, Sugimori, and Tanno (2009) tested high and low schizotypy individuals, all without mental illness, on three language and lateralization tasks. A line-drawing task measured the lateralization of handedness in each individual, showing high schizotypy individuals perform equally well with their right and left hands, while low schizotypy individuals perform better with their left hands. Then, the lateralization of motor speed and force was measured using finger tapping, showing schizotypal individuals retain functional lateralization with regards to motor functions.

Finally, language lateralization was tested using a dichotic listening task, in which participants pressed a button with an indicated hand when they heard a target word after different words were presented to each ear. Low schizotypal participants responded more quickly with their right hand

Letters because language is lateralized to the left hemisphere.

High schizotypal individuals, however, responded equally quickly to words presented in each ear, showing a lack of lateralization in semantic processing. Taken together, the results of this study demonstrate that high schizotypal individuals show less lateralization for motor control and semantic processing, supporting Crow’s theory of schizophrenia and lateralization.

Crow’s theory has also been supported by functional imaging studies. Bleich-Cohen, Hendler, Kotler, and Strous (2009) used functional magnetic resonance imaging (fMRI) to test language-related lateralization in schizophrenic patients during their first psychotic episode.

Participants were presented nouns and asked to think of related verbs during an fMRI scan. They were also scanned while passively listening to classical music. The results showed schizophrenic patients had significantly less lateralization in two regions involved in language, Broca’s area and Wernicke’s area, than controls during the language task, but not while listening to music. Further analysis showed the decrease in lateralization was due to higher activation in the right hemisphere. In support of Crow’s hypothesis, Bleich-Cohen et al. (2009) also found a significant correlation between the severity of a patient’s positive symptoms and decreased lateralization. Because individuals with schizophrenia were tested during their first psychotic episode, before long-term antipsychotic use, the loss of brain asymmetry likely reflects developmental changes in language lateralization (Bleich-Cohen et al., 2009).

Crow’s theory is also supported by genetic research.

Tolosa, Sanjuán, Dagnall, Moltó, Herrero, and deFrutos (2010) found higher expression of FOXP2, a gene involved in human language impairment, in the right hemisphere of individuals with schizophrenia. They also saw a significant correlation between FOXP2 polymorphisms and language impaired schizophrenic patients. While it is surely not the only gene that is involved in both schizophrenia and language, FOXP2 provides strong evidence for the evolution of language also conferring a vulnerability to schizophrenia. Combined, these studies lend support to Crow’s theory that schizophrenia evolved as a byproduct of the highly lateralized language brain (Asai et al., 2009; Bleich-Cohen et al., 2009; Tolosa et al., 2010).

Sociality Schizophrenia is a disorder of consciousness and produces a range of social impairments. Schizophrenic patients have shown deficits in many social activities, such as judging the direction of eye gaze, interpreting emotional face expressions, and decision-making (Burns, 2006). Anatomically, schizophrenia is accompanied by changes in the neural connectivity of social brain regions, particularly the prefrontal cortex (Burns, 2004). Because of the large commonalities between social brain anatomy and regions affected in schizophrenia, some have hypothesized schizophrenia evolved as a byproduct of the social brain (Burns,

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2004).

The social brain has been evolving for millions of years.

Although neocortex size and interhemispheric connectivity has been increasing since roughly 15 million years ago, H. sapiens probably did not develop a full theory of mind (ToM) until 100,000 years ago (Burns, 2004). ToM is the assumption that all people have mental states and can infer the mental states of others (Burns, 2004). The prefrontal cortex is crucial in developing and maintaining a functional ToM. In normal humans, ToM is developed around age four, at which point children are able to distinguish between the truth and false beliefs of others (Frith, 2004). The genetic events that led to the development of ToM and the social brain, which evolved before humans left Africa, could have allowed vulnerable regulatory genes to be maintained in the population.

Specialized brain regions and increased neural connectivity, both of which are disturbed in schizophrenia, characterize the social brain. While each brain area functions as a relatively independent module in less social animals, several brain regions work together in humans to allow complex social interactions. The fusiform gyrus in the temporal lobes recognizes the identity of faces. Simultaneously, the prefrontal cortex is involved in personality, planning, and rational thought. The amygdala, which also recognizes the emotional content of faces and forms social bonds, plays a role in connecting the higher and lower cortical regions that contribute to physiological responses (Burns, 2004). Each component of the social brain is connected, which allows regions to interact and makes the social brain a functional, integrated machine.

Schizophrenic individuals not only have reduced activity in the individual components of the social brain, but they also display a breakdown of the connections between parts. Functional imaging studies have shown reduced activity in the prefrontal cortex and amygdala of schizophrenic individuals (Burns, 2004). The breakdown of the connections between the prefrontal cortex and the other regions of the social brain seen in schizophrenia has caused some researchers to propose a “dysconnectivity hypothesis of schizophrenia,” which posits that the symptoms of schizophrenia are caused by an interruption in communication between brain regions (Vogeley & Falkai, 1998).

The interruptions of communication between brain regions could be the result of abnormal neural development caused by impaired genes (Burns, 2004). Neural development in normal individuals follows a process that continues into adolescence. Neurons are born in the subventricular zone then migrate to their respective locations, where they differentiate and form synapses. A long period of cell death and synapse rearrangement then follows (Breedlove et al., 2010). This final phase of development has been implicated in the structural and functional abnormalities in schizophrenia. Too much or too little cell death and aberrant connections would produce atypical connectivity, particularly affecting the social brain and possibly causing the social impairments seen in schizophrenia (Burns, 2004).

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Because this process lasts into adolescence, its negative effects could appear in late adolescence, which coincides with development of schizophrenia symptoms. Given many of the areas affected in schizophrenia are parts of the social brain, and the development of these areas is controlled by regulatory genes, it is conceivable that adaptive regulatory genes underlying development make humans vulnerable to schizophrenia (Burns, 2004).

In addition to the physical and developmental changes, the social brain perspective lends theoretical insight into the development of some positive and negative symptoms of schizophrenia. Negative schizophrenia shares symptoms, such as poor communication, stereotyped behavior, and lack of speech with autism, another disorder of the social brain. An impaired ToM, resulting from overly rapid neural development, characterizes autism. Delayed neural development, as seen in schizophrenia, also causes an impaired ToM (Crespi & Badcock, 2008). ToM impairment in schizophrenia could explain negative symptoms, such as flat affect, if the individual lacks awareness that others do not understand his or her mental state (Frith, 2004). Similarly, disorganized speech assumes that the listener shares the same train of thought. Other positive symptoms, such as paranoid thoughts of persecution, could result from impaired mind reading abilities (Burns, 2006). While a damaged ToM does not explain some of the symptoms of schizophrenia, including hallucinations, thought insertion, and some negative symptoms, there is increasing evidence linking the disorder to autism-like ToM impairments.

In a salient cognitive study by Corcoran et al. (1995), the theory of mind was directly examined in individuals with schizophrenia. All types of schizophrenic patients were tested in a hinting task in which they were required to infer a character’s intentions based on an obvious hint.

They found that schizophrenic individuals with negative symptoms performed the worst, and those with incoherence and paranoid delusions also performed poorly. The results of this study are consistent with the hypothesized ToM deficits in some types of schizophrenia, lending support to the model. Furthermore, a recent functional imaging study by Brüne et al. (2011) corroborated these results.

People at-risk for schizophrenia, manifest schizophrenic patients, and healthy controls were asked to infer the mental states, beliefs, and intentions of cartoon characters during an fMRI scan. The results showed that control and at-risk subjects activated the ToM network similarly, but at-risk subjects activated some regions more extensively, including a region normally reserved for more emotional stimuli. This suggests at-risk patients may compensate for deficits by recruiting more brain regions that overlap with the ToM network (Brüne et al., 2011). Finally, patients with schizophrenia showed the least activation during the inference task. This study exposes clear changes in the ToM network in schizophrenic and at-risk individuals, supporting the theory that schizophrenia is an impairment of the social brain.

Furthermore, using three different ToM tasks and four 10 | neurogenesisjournal.com | Fall 2011 | Vol 1 Issue 1

Letters different language comprehension tasks, Gavilán and García-Albea (2011) found schizophrenic patients’ difficulties in understanding the mental states of others is closely connected to their impairments in understanding figurative language. ToM is correlated to language comprehension primarily at a semantic level, where the listener must infer the meaning of figurative language, such as metaphors, ironies, and proverbs. The interdependence between inferring meaning from language and understanding another’s mind could highlight a connection between Crow’s language impairment theory and the social brain theory.

Human social interactions are intricately linked to, and in some cases dependent on, language. While the theories differ in their evolutionary time course, they both rely on an evolutionary paradigm. Furthermore, both theories cite developmental differences in lateralization and the social brain, respectively. An integration of the two theories, however, would depend on a link between lateralization and the function of the social brain. This comprehensive theory would account for all of the core schizophrenia symptoms, as Crow’s theory explains the positive symptoms, while the social brain theory accounts for the negative symptoms. The combination of Crow’s theory and the social brain theory would introduce new research questions that provide insight into the causes of schizophrenia.

Creativity Anecdotal evidence has linked mental disorders to creativity for years. People cite highly successful individuals, such as John Nash and Jack Kerouac, as examples of highly creative schizophrenics. Though the evidence linking schizophrenia and a creative advantage is lacking, schizotypy is significantly correlated to creativity. Indeed, close relatives of schizophrenic patients are more successful in scholarly, academic, and artistic professions (Pearlson & Folley, 2008). Similarly, the population of creative individuals shows a higher prevalence of mental disorders (Rubinstein, 2008). Creativity, defined as the ability to produce original and useful objects or ideas, could increase the reproductive success of the individual through sexual selection or improved problem-solving skills (Eysenck, 1996). This set of observations has caused some to propose that schizophrenia and creativity have common genetic origins, and the genes that cause schizophrenia could confer an evolutionary advantage on schizotypal individuals (Weinstein & Graves, 2002; Fisher et al., 2004; Rubinstein, 2008).

Antagonistic pleiotropy refers to the phenomenon of a single gene coding for multiple characteristics, some of which are beneficial and some harmful (Keller & Miller, 2006). These genes are able to persist in the population if their helpful characteristics outweigh their negative characteristics. Although the maladaptive consequences of schizophrenia are disastrous, the creative relatives of schizophrenic individuals could have a reproductive advantage over the general population, thereby propagating genes that, in the correct combinations, cause schizophre-

Letters nia. This “kin theory” proposes that schizophrenia persists because those with an incomplete set of schizophrenia genes have an evolutionary advantage. Several positively selected genes associated with both creativity and schizophrenia have been found in the normal population (Crespi et al., 2007). Other genes that link schizophrenia risk and openness to experience, a predictor of creativity, have also been found (Crespi et al., 2007).

The validity of the creativity theory of schizophrenia depends on the reproductive success of creative schizotypal individuals. Nettle and Clegg (2006) investigated the relationship between creativity, schizotypal personality traits, and mating success in a sample of British adults. The level of schizotypy was measured using four dimensions: unusual experiences, cognitive distortions, impulsive nonconformity, and introvertive anhedonia. There was a significant positive correlation between unusual experiences, impulsive non-conformity, and creativity, which lead to an increase in mating success. Conversely, there was a strong negative correlation between introvertive anhedonia, creativity, and number of partners. Overall, these results support the hypothesis that schizotypal personality traits increase reproductive success because of creativity. However, it is still unknown whether this reproductive advantage is sufficient to offset the reduced fecundity caused by schizophrenia.

Other anatomical and behavioral studies have found connections between schizotypy, schizophrenia, and creativity. Weinstein and Graves (2002) found a high positive correlation between schizotypal personality traits, creativity, and cerebral lateralization. They showed increased right hemisphere ability is related to creativity using a dichotic listening task. The right hemisphere of schizotypal individuals had a lower threshold for processing, suggesting it was strengthened relative to the left hemisphere (Weinstein & Graves, 2002). Because the right hemisphere is involved in holistic processing, increased right hemisphere dominance could cause the individual to make remote or loose associations between concepts, a key characteristic of creativity and divergent thinking (Fisher et al., 2004).

This increased hemispheric connectivity could lead to increased levels of creativity but also to the positive symptoms of schizophrenia. Furthermore, creativity is heavily dependent on language, a function resulting from cerebral lateralization. The common neural basis for language and creativity suggests they are highly connected, perhaps both as genetic adaptations with a risk of schizophrenia.

To further explore the connections between schizotypy, language, and creativity, Humphrey, Bryson, and Grimshaw (2010) examined two potential relationships between schizotypy and metaphor processing in high and low schizotypal individuals. Although degradation of the semantic system seen in high schizotypy could cause poor metaphor processing, increased activation of the right hemisphere may improve metaphor processing.

The results, however, did not indicate a deficiency or improvement in metaphor processing, reflecting a difference

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between schizotypy and schizophrenia. Nevertheless, the high schizotypy group was more likely to identify a metaphor as applicable to the situation, which the authors interpreted as a sign of reduced cognitive inhibition, despite previous results showing schizotypy and creativity are not linked to reduced cognitive inhibition (Humphrey et al.

2010). Green and Williams (1999) found significant correlations between schizotypy and the number of unique responses produced on a divergent thinking task, but they found no correlation between divergent thinking and reduced cognitive inhibition. These results show the causal link between schizotypy, creativity, and language is more complicated than reduced inhibition (Green & Williams, 1999).

There are several other weaknesses in the creativity theory of schizophrenia. First, a study by Miller and Tal (2007) showed openness to experience and intelligence, not schizotypy, to be predictors of creativity. Because schizotypy is correlated with openness, the creativity seen in schizotypal individuals could result from increased openness rather than schizophrenic traits (Miller & Tal, 2007). Second, the strong negative correlation between schizophrenia’s negative symptoms and creativity undermine their connection. A causal link between schizophrenia and creativity genes would better explain positive than negative symptoms.

Furthermore, it is important to note that the creative advantage does not lie in schizophrenic individuals. While there has always been a complicated relationship between “genius” and “madness,” it is evident that severe schizophrenia is not conducive to creativity. In a study by Rubinstein (2008), the divergent thinking of schizophrenic patients was lower than that of patients suffering from major depression, anxiety, or personality disorders. Despite some cognitive similarities between schizophrenic and creative individuals, including ability to connect novel information, schizophrenic patients do not show creativity, perhaps because of verbal deficiencies and cognitive impairments. Indeed, the most productive, famous schizophrenics were only able to work when their symptoms abated (Fisher et al., 2004). This brings up the question of where the threshold for “genius” and “madness” lies. More research is needed to firmly establish a causal connection between creativity genes, their reproductive advantage in schizotypal individuals, and the onset of schizophrenia.

Conclusion The language, social brain, and creativity theories of schizophrenia evolution each have their strengths and weaknesses. Though alone each theory provides unique insight into the paradoxical evolution of schizophrenia, none of the theories account for the full spectrum of symptoms or the many neural changes observed. A combination of these three theories, however, has the potential to provide a comprehensive explanation of the evolutionary origins of schizophrenia. It is therefore necessary for future research to investigate the intersections between each theory with Vol 1 Issue 1 | Fall 2011 | neurogenesisjournal.com | 11

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a focus on common underlying structural, functional, genetic, and developmental abnormalities in relation to language, the social brain, and creativity.

Although a comprehensive evolutionary model of schizophrenia provides valuable insight into the causes of the disorder, its largest contributions would be clinical and social applications. Knowledge of the evolution of schizophrenia could lead to improved treatments that target the most fundamental underlying brain changes. The model would also enhance understanding of the development of schizophrenia over an individual’s life, which could lead to earlier identification. Finally, a complete evolutionary model may reduce the stigma associated with schizophrenia if people come to view the disorder as an evolutionary byproduct of normal, adaptive functions.

Evolution is not optimal. Natural selection does not engineer perfect organisms, nor does it anticipate challenges the future environment may hold. The best evolution can accomplish is to improve existing models, sometimes resulting in necessary tradeoffs. The human brain and its complex functions, including language, sociality, and creativity, are a testament to evolution’s power. Schizophrenia, however, may be the price that humans must pay for the essential traits that have brought so much success.

American Psychiatric Association. (2000). Diagnostic and statistical manual of mental disorders (Revised 4th ed.). Washington, DC Asai, T., Sugimori, E. and Tanno, Y. (2009). Schizotypal personality traits and atypical lateralization in motor and language functions, Brain and Cognition, 71, pp. 26–37.

Bleich-Cohen, M., Hendler, T., Kotler, M., Strous, R.D. (2009). Reduced language lateralization in first-episode schizophrenia: An fMRI index of functional asymmetry. Psychiatry Research Neuroimaging, 171, 82-93.

Breedlove, S.M., Watson, N.V., Rosenzweig, M.R. (2010). Biological Psychology, 6th edition. Massachusetts, Sinauer Associates, Inc. Brüne, M. (2004). Schizophrenia – an evolutionary enigma? Neuroscience and Biobehavioral Reviews, 28, 41-53.

Brune, M., Ozgurdal, S., Ansorge, N. Graf von Reventlow, H., Peters, S., Nichols, V., Tegenthoff, N. Juckel, G., Lissek, S. (2011). An fMRI study of “theory of mind” in at-risk states of psychosis: Comparison with manifest schizophrenia and healthy controls. Neuroimage, 55, 329-337.

Burns, J.K. (2004). An evolutionary theory of schizophrenia: Cortical connectivity, metarepresentation, and the social brain. Behavioral and Brain Sciences, 27, 831-885.

Burns, J.K. (2006). Psychosis: A costly by-produce of social brain evolution in Homo sapiens. Progress in Neuro-Psychopharmacology & Biological Psychiatry, 30, 797-814.

Corcoran, R., Mercer, G., Frith, C.D. (1995). Schizophrenia, symptomatology and social inference: Investigating “theory of mind” in people with schizophrenia. Schizophrenia Research, 17, 5-13.

Crespi, B., Summers, K., Dorus, S. (2007). Adaptive evolution of genes underlying schizophrenia. Proceedings of the Royal Society B, 274, 28012810.

Crespi, B., Badcock, C. (2008). Psychosis and autism as diametrical disorders of the social brain. Behavioral and Brain Sciences, 31, 241-320.

Crow, T.J. (1997). Is schizophrenia the price that Homo sapiens pays for language? Schizophrenia Research, 28, pp. 127–141.

Crow, T.J., (2000) Scizophrenia as the price that Homo sapiens pays for language: a resolution of the central paradox in the origin of the species.

Brain Research Reviews, 31, 118-129 Darwin, C. (1859). On the Origins of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life.

Eysenck, H.J. (1996). The measurement of creativity. In M.A. Boden (Ed.),

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Letters Dimensions of Creativity (pp. 199-242). MA: MIT Press. Fisher, J.E., Mohanty, A., Herrington, J.D., Koven, N.S., Miller, G.A., Heller, W. (2004).

Neuropsychological evidence for dimensional schizotypy: Implications for creativity and psychopathology. Journal of Research in Personality, 38, 24-31.

Frith, C.D. (2004). Schizophrenia and theory of mind. Psychologican Medicine, 34, 385-389.

Gavilán, J.M., García-Albea, J.E. (2011). Theory of mind and language comprehension in schizophrenia: Poor mindreading affects figurative language comprehension beyond intelligence deficits. Journal of Neurolinguistics, 24, 54-69.

Green, M.J., Williams, L.M., (1999) Schizotypy and creativity as effects of reduced cognitive inhibition. Personality and Individual Differences, 27, 263–276.

Humphrey, M.K., Bryson, F.M., Grimshaw, G.M. (2010). Metaphor processing in high and low schizotypal individuals. Psychiatry Research, 178, 290-294.

Keller, M.C, Miller, G. (2006). Resolving the paradox of common, harmful, heritable, mental disorders: Which evolutionary genetic models work best? Behavioral and Brain Sciences, 29, 385-452.

McGuffin, P., Owen, M.J., Farmer, A.E., (1995). Genetic basis of schizophrenia. Lancet, 346, 678-682.

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Nettle, D., Clegg, H. (2006) Schizotypy, creativity and mating success in humans, Proceedings of the Royal Society London (B Biol Sci, ), 273, pp. 611–615.

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Link between brain reward pathways and sodium appetite: Regulation of DARP-32 in response to sodium deficiency Sarah Hochendoner1, Wolfgang Liedtke2 Duke University, Durham, North Carolina 27708 Duke University Medical Center, Durham, North Carolina 27708 Correspondence should be addressed to Sarah Hochendoner (sarah.hochendoner@duke.edu) 1 2

ABSTRACT: In mammals, sodium appetite is a highly motivated behavioral state triggering a strong drive to ingest salt, which can be evoked by prolonged sodium deprivation, stress-evoked ACTH (adrenocorticotropic hormone) infusion, and reproduction, ceasing only upon gratification. Since the hypothalamus is the key regulator of reflexive and primitive drives, it is the area of focus for central nervous system sodium appetite mechanisms (Denton, 1996). By integrating the actions of physiological mechanisms involved in body fluid regulation, the hypothalamus plays a key role in regulating osmotic balance and correcting homeostasis in times of dysequilibrium.

In order to identify significantly regulated genes that may play a functional role in the brain’s response to sodium depletion, a genome-wide transcriptome analysis was performed using microarrays on whole brain and hypothalamic tissue RNA from Na+ deprived and control mice. Of several regulated genes, the 32-kDa dopamine-regulated and cyclic AMP-regulated phosphoprotein (DARPP-32) emerged as significantly upregulated in hypothalamus, confirmed by qRT-PCR (quantitative real-time PCR), an independent gene profiling method. DARPP-32 is an intracellular mediator of dopamine implicated in the actions of drugs of abuse. It is found in high levels in the nucleus accumbens and appreciably in the hypothalamus (Nairn, 2004). Implementing Gene Set Enrichment Analysis (GSEA) showed that gene sets previously linked to addiction were significantly enriched in the hypothalamus of mice with sodium appetite.

Against this background, this study interrogates the neural mechanisms of Na+ appetite, from the cellular, molecular, and circuit perspectives, with a focus on DARPP-32.

Through immunohistochemical studies, DARPP-32 expression was found to be upregulated in the lateral hypothalamus of sodium-deficient animals as compared to controls. It was also found to co-localize with neural plasticity regulator, ARC. Examining these processes not only provides a connection to mechanisms of systemic hydromineral homeostasis, but also links Na+ deficiency to motivational and reward pathways in the brain. Although salt appetite has evolved as a homeostatic process for millions of years, drugs of abuse are a modern phenomenon, likely taking over the already established evolutionary survival mechanisms in order to achieve gratification.

Introduction Sodium (Na) is a trace element in most regions of the world, yet it plays a critical physiological role in mammals, greatly affecting normal growth and development as well as the maintenance of membrane potentials (Morris et al., 2008). Land dwelling animals have thus evolved with powerful mechanisms to ingest sufficient amounts of this trace element, an evolutionary development that has led to sodium appetite in virtually all land-dwelling mammals.

Due to the importance of maintaining a precise body fluid balance, the concentrations of water and sodium are adjusted by way of ingestion and excretion, strictly regulated by neuroendocrine control systems (Geerling and Loewy, 2008). In most mammals, sodium depletion results in marked physiological and behavioral changes, chiefly the drive to intake sodium ( Johnson, 2007). Sodium appetite, a highly motivated behavioral state triggering a strong drive to ingest salt, can be evoked by prolonged sodium deficiency in many animals and persists until salt intake.

Additional triggers of sodium appetite include reproduc-

tion and ACTH in response to stress (Denton, 1999).

Sodium-deficient rats demonstrate an appetite highly specific for sodium as compared to other salts (Denton, 1988), and they will perform increasing amounts of work in the form of bar pressing in order to obtain sodium (Wagman, 1963). This robust motivational drive can be gratified by rapid consumption of sodium, a behavior which maintains a high survival value. As an example, if an animal low in sodium were at risk for attack by a predator, the instinctual circuitry governing sodium appetite would enable the animal to quickly ingest this essential ion, and immediately flee in order to avoid predation and ultimately, survive. Another element of the gratification behavior causes ceasing of sodium intake before the gut has appreciably absorbed sodium from the recently consumed fluid (Denton, 1988).

It is interesting to note that while sodium-depleted animals willingly drink concentrated sodium solutions, sodium-replete animals may intake only a small amount of 0.3 M NaCl (Denton, 1988) and find this hypertonic solution to be aversive. These differences indicate a neural change Vol 1 Issue 1 | Fall 2011 | neurogenesisjournal.com | 13

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that makes the intake of concentrated sodium more rewarding. Due to the critical role of sodium in metabolic processes and the maintenance of membrane potential and osmotic balance, sodium deprivation leads to dysequilibrium and subsequent organismal stress. Sodium-appetite and -reward are plastic mechanisms, meaning that salt is more palatable after its depletion, and repeated stresses of sodium depletion result in an increase in subsequent consumption. The phenomenon of sodium appetite sensitization only occurs, however, over two to four sodium depletions, where instead of increased sodium consumption, a plateauing effect leads to a sustained and stable subsequent intake (Morris et al., 2008).

Reward is a neurally-encoded emotional concept that is also critical to survival, as animals must learn the appropriate circumstances under which to engage in necessary behaviors, such as obtaining food and mating. In the forebrain, the nucleus accumbens (NAc) is activated during reward, such as palatable food ingestion or exposure to addictive drugs. The accompanying neural responses to these “natural rewards� share similarities with the reward perceived by taking drugs of abuse. In both cases, levels of synaptic dopamine rise in the striatum and the NAc. This increase in extracellular dopamine level prompted by the actions of all drugs of abuse occurs mainly via pathways from the ventral tegmental area (VTA) (Hyman et al., 2006). Microdialysis studies of the NAc have shown that sodium-depleted rats show increased extracellular levels of dopamine when permitted to gratify, suggesting that perhaps the dopaminergic system may contribute to the perceived increase in the reward value of sodium (Hoebel, 1989).

The hypothalamus (HT), implicated in regulation of instinctive behaviors including homeostatic mechanisms and hormonal behavioral rhythms, is also highly involved in the neural circuitry of motivational behaviors. This circuit, that includes interconnections with the NAc and the VTA, is involved in regulation of ingestive behaviors (Kalivas and Volkow, 2005; Ahmed et al., 2005). The HT is critical in integration of the many physiological systems involved in fluid homeostasis. HT mechanisms control both the retention and excretion of sodium, including sensors prompting maintenance of hydromineral homeostasis by reacting to deviations in sodium concentration. Thus, the HT plays a key role in regulating osmotic sodium and water balance, causing physiological mechanisms to correct homeostasis in times of dysequilbrium (Denton et al., 1996). These physiological changes, along with the effects of many other incoming stimuli, give rise to emotions, intentions, and behaviors.

The lateral hypothalamus, specifically, is implicated in ingestive behavior, sending projections to the NAc to provide feedback concerning internal homeostasis and to downstream centers involved in motor output (Kelley, 2004). Lesions of the lateral hypothalamus have been shown to impair sodium appetite (Schulkin, 1985; Wolf, 14 | neurogenesisjournal.com | Fall 2011 | Vol 1 Issue 1

Articles 1964). Another element of the lateral hypothalamus pertinent to this study concerns the role of the orexinergic population of neurons in the lateral hypothalamus in reward processing and motivational behaviors. Orexins (also known as hypocretins) are neuropeptides produced exclusively in the lateral hypothalamus (Cason, 2010). Although they were originally discovered to have implications in activation and feeding behaviors, narcolepsy, and arousal, recent studies have strongly suggested their role in reward processing and drug addiction in the lateral hypothalamus.

As shown in other studies, stimulation of LH orexinergic neurons leads to reinstatement of morphine preference by driving a neural circuit of orexinergic neurons projecting to the VTA (Harris et al., 2005), and intracerebroventricular infusion of orexin caused a reinstatement of cocaineseeking in rats (Boutrel, 2005). Additionally, orexinergic neurons project to reward-related brain regions such as the NAc and VTA, further implicating this region in reward circuitry (Harris, 2005). Based on the essential role of the lateral hypothalamus in motivated behavior in response to drugs of abuse, it is a relevant locus to explore in this investigation of hypothalamic regulation of sodium appetite.

In order to identify significantly regulated genes that may play a functional role in the brain’s response to sodium depletion, a transcriptome analysis using microarrays was performed on brain and hypothalamic tissue RNA from sodium deprived and control mice. Of many regulated genes, the 32-kDa dopamine-regulated and cyclic AMPregulated phosphoprotein (DARPP-32) was found to be appreciably upregulated in the HT. A significant amount of evidence has implicated the role of DARPP-32 in the actions of drugs of abuse, including opioids, cocaine, and amphetamines; DARPP-32 has also been investigated in the processing of other rewarding stimuli, such as highlipid food (Nairn et al., 2004). When initially identified, DARPP-32 was thought to serve only as a target for dopamine and protein kinase A (PKA) in brain regions with abundant dopaminergic neurons and processes (Walaas et al., 1983). However, continued research on the biochemical, transcriptional, and electrophysiological actions of the phosphoprotein has shown its diverse functions in neurotransmission in many areas of the brain, in conjunction with a variety of neurotransmitters and other neuromodulators. DARPP-32 has best been characterized for mediating dopamine signaling in the medium spiny neurons of the striatum (Svenningsson et al, 2004). It is found in high levels in the nucleus accumbens and the hypothalamus. Phosphorylation at Threonine34 (Thr34)

by PKA transforms DARPP-32 into a high-affinity inhibitor of the multifunctional serine/threonine protein phosphatase, PP-1 (Hemmings et al., 1984). Activation of the dopamine D1 receptor initiates this cascade, leading to inhibition of PP-1 causing an increase in the phosphorylation of ion channels and neurotransmitter receptors involved in synaptic function. More recent studies have revealed that DARPP-32 phosphorylation occurs via a variety of mechanisms in various brain regions. For ex-

Articles ample, other phosphorylation sites can mediate the effect of DARPP-32, such as phosphorylation at Thr75, which functions in an inhibitory manner, inhibiting PKA and the signaling via the PKA/Thr34-DARPP-32/PP-1 cascade (Svenningsson et al., 2004). Although originally identified as a cytoplasmic protein, DARPP-32 has also been shown to display increased accumulation in the nucleus during administration of drugs of abuse or in reinforcement learning for high-lipid food pellets (Stipanovich et al., 2008). The focus of the following study is to provide evidence for a link between sodium appetite and brain reward pathways, establishing a more comprehensive map of the neural pathways involved in sodium appetite and demonstrating a relationship with motivational behaviors, reward, and addiction.

Experimental Protocol Sodium appetite of mice for microarray and GSEA studies was achieved via two different methods: (1) injection of a diuretic, furosemide, to cause true depletion of sodium and (2) via chronic ACTH subcutaneous (s.c.) infusion, to mimick the neuroendocrine effects of physical stress and eliciting subsequent sodium intake (n = 5-6 per group) (Figure 1).

A genuine sodium deficit can be produced through injection of the diuretic furosemide, which increases sodium intake, rapidly correcting for the induced sodium deficit

Figure 1: Experimental protocol detailing induction of sodium appetite Sodium appetite was induced either via two days of injections with the diuretic furosemide, causing physiological depletion of sodium or 12 days of treatment with ACTH, leading to a chronic stress model that causes increased intake of sodium.

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(Denton, 1988). Instead of generating a genuine need for sodium due to removal of sodium, another method for inducing sodium appetite was based upon a stress model.

ACTH is secreted by the anterior pituitary in response to stress, causing increased production of corticosteroids in the adrenal cortex. ACTH most likely functions via the abundant synthesis of glucocorticoids and mineralocorticoids, which act on the brain via glucocorticoid and mineralocorticoid receptors. In this study, ACTH was administered for 12 days (as further detailed in the methods section), thereby mimicking a model of chronic, as opposed to acute, stress. Systemic administration of ACTH caused a large specific increase in NaCl intake in rabbits, mice, and rats, likely reflecting the effects of stress. Some animals such as rabbits and mice may need to adapt to severe environmental circumstances, with relatively low levels of sodium in the available vegetation. Under these circumstances, a hormone cascade invoked by stress leading to a rapid intake of any available sodium would be highly advantageous, especially for females in preparation for pregnancy, when sodium is essential for the proper growth and development of the pups (Denton et al., 1999). Additionally, studies on salt appetite in humans have indicated that increased stress may play a role in greater salt consumption, perhaps ultimately leading to hypertension (Henry, 1988).

Only two groups of animals were studied – furosemide sodium depleted rats and control rats (n = 3-4 per group).

Gene set enrichment analysis (GSEA) is a computational method that determines whether an a priori defined set of genes shows statistically significant, concordant differences between two biological sets. Microarray data serves as the input information, with one set of experimental data compared to a previously characterized gene set, a group of genes that share common biological or regulatory function (Subramanian, 2005). The comparison gene sets utilized in GSEA have been compiled by researchers, gathering microarray data as produced from a range of studies in order to produce gene sets composed of genes that are expected be regulated in a particular behavioral process. Gene sets chosen often signify pathways hypothesized to be regulated with the microarray data; in this case, four addiction gene sets were chosen that have been strongly implicated in addiction processes, including pathway gene sets for opioids, cocaine, alcohol, and nicotine. Additionally, in order to make comparisons with the addiction gene sets, all available pathway gene sets of the approximate size of neural activity gene sets were also examined, totaling 54 investigated gene sets. After analysis, GSEA provides an output value representing the degree to which genes within the set are up-regulated or downregulated within the microarray data comparison set. In this way, the comparison gene set which shows the greatest association with the microarray data may be determined, therefore implicating similarity in regulatory pathways and possibly biological function.

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Figure 2: Microarray and GSEA studies from the hypothalamus (A) A transcriptome analysis utilizing hypothalamic tissue RNA from sodium deprived and control mice was performed using microarrays encompassing total genome wide coverage. The genes showing the greatest regulation were either linked to gratification pathways, monoaminergic signaling, or belonged to addiction gene sets. Each of the genes in this figure were regulated by at least one of the sodium appetite conditions as compared to control. Of these, in particular, DARPP-32, ARC, and DRD1 emerged as significantly upregulated in HT as compared to the rest of the brain. A rapid loss of gene regulation was observed upon gratification. (B)This figure shows qRT-PCR data validating the RNA gene expression as displayed in the microarray. Whereas the red bars represent reversal in gene expression as caused by gratification, the pink bars represent genes that do not reverse after 10 minutes of sodium consumption.(C) Results from GSEA, including normalized enrichment scores and nominal p-values, indicate a remarkable increase in enrichment score and decrease in p-value for the opioid and cocaine gene sets when both conditions of sodium appetite are combined. The opposite results were discovered in animals allowed to gratify. (D) The left-hand portion shows that there is a striking loss of gene regulation in the gratification state, via analysis of the top 100 genes regulated in sodium appetite as compared to control. The right-hand graph shows the direction of gene expression as prompted by gratification compared to sodium appetite through analysis of the top 600 regulated genes.

Background Experimentation The novel outcomes of both the microarray and GSEA studies conducted in the lab gave significant credence to the subsequent immunohistochemical analysis and therefore will be discussed here before examining protein expression. In analyzing sodium depleted animals versus controls, microarrays encompassing total genome wide coverage displayed regulation of hypothalamic genes as compared to the rest of the brain (Figure 2A), with the most highly regulated genes originating from either addiction gene sets or having links to dopamine signaling and reward, including DARPP-32, dopamine receptors 1 and 2, and the immediate early gene ARC. qPCR confirmed the regulated genes as detected by microarray (Figure 2B).

However, a rapid loss of concerted gene regulation was observed upon gratification, in animals permitted to drink a 0.3M NaCl solution for 10 minutes.

Next, microarray data was further processed to be used in GSEA. Gene sets compiled from previously characterized microarray studies of addiction showed particular coregulation with the gene sets derived from the hypothalamisodium-deprived mice, as well as those from ACTH induced sodium appetite. The most significantly enriched 16 | neurogenesisjournal.com | Fall 2011 | Vol 1 Issue 1

gene set was among opioid addiction-associated genes.

Combination of the gene sets for both conditions of sodium depletion also greatly increased significance levels, which offers a novel finding (Figure 2C). For example, in the case of gene sets that show decreased correspondence upon combination of the two conditions, this would express that the generation of sodium appetite occurred through eliciting participation of different genes and regulatory pathways. However, because the respective combination of these two conditions actually produced highly increased significance levels with addiction related gene sets, these results implicate that the two different stimuli giving rise to sodium appetite actually share genes with each other that are encompassed in those gene sets previously attributed to addiction. Assessed more broadly, these results show that two different stimuli evoke shared genes previously implicated in another process to give rise to the same urge. After gratification, as was alluded to in the microarray data, there was no increase in enrichment upon combination of the two groups, again implicating a loss of gene regulation, at least of the genes contained within these particular sets (Figure 2D). Finally, no significantly enriched sets were found in the remainder of the brain

Articles (the rest of the brain after removal of the hypothalamus).

In order to further investigate the participation of reward pathways and motivational behaviors in an in vivo setting, the behavior of the animals was recorded when dopamine receptor agonists were administered. The functions of dopamine receptors have been highly studied in their functioning in terms of reward processes and also selfadministration of abused drugs (Caine et al., 2007). Sodium-depleted rats were administered antagonists for either dopamine receptor 1 (SCH23390) or dopamine receptor 2 (Raclopride), each with two different dose conditions.

Upon antagonism of each of the receptors, the animals drank decreased amounts of NaCl solution. Animals administered a higher dose of antagonist showed even more notable decreases in gratification behavior (Figure 3A).

Additional studies with DRD1 knock-out mice demonstrated the specificity of SCH23390, with an absence of off-target effects; as the knock-out mice still showed normal depletion invoked sodium appetite, however, this re-

Figure 3: The role of dopamine receptors and reward pathways in sodium appetite (A) Upon antagonism of both DRD1 (with SCH23390) and DRD1 (with Raclopride), the animals drank decreased amount of the NaCl solution, with the set of animals administered a 0.2mg/kg dose of antagonist showing even more considerable decrease in gratification behavior as compared to those receiving the 0.1 mg/kg dosage.(B) In examination of the effects of the dopamine receptor antagonists on thirst, another innate ingestive behavior, while the DRD1 antagonist had no effect on water intake, the DRD2 antagonist slightly reduced thirst behaviors.(C) Additional studies with DRD1 knockout mice demonstrated the specificity of SCH23390, with an absence of offtarget effects, however as the knock-out mice still showed normal depletion invoked sodium appetite, this result may suggest an up-regulation of alternative pathways.(D) This bar graph indicates the average sodium consumption in 4 sodium depleted rats after insertion of intrahypothalamic catheters and injection of the DRD1 antagonist as compared to microinjection with aCSF. (E) This diagram shows the anatomical placement of the cannula within the LH in each of the four animals that showed significant reduction of sodium appetite in response to the DRD1 antagonist.

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sult may suggest an up-regulation of alternative pathways (Figure 3C).

Although multiple dopamine receptor antagonism experiments were conducted, these procedures involved intraperitoneal injection of the drug antagonists, causing possible systemic response leading to gratification behaviors, without evidence of the neural location of antagonist action. To achieve higher specificity in the neural regions of interest, rats were microinjected with SCH23390 into their lateral hypothalamus area (Figure 3D). However, due to the possibility of error or damage in cannula placement, only animals that showed robust sodium appetite after an aCSF control solution (displaying an intact lateral hypothalamus) were injected with the antagonist drug; here, it was reasoned that for the sodium deprived animals that did not show rapid gratification behavior, their LH were likely damaged during cannula placement. Thus four animals were injected with 200 nL of 100 nM SCH23390, causing a drastic reduction of sodium appetite in all animals, with complete elimination of sodium consumption in two animals. The exact placement of each of these four cannula are shown in Figure 3E. An examination of the effects of the dopamine receptor antagonists on thirst, another innate ingestive behavior, revealed that while the DR1 antagonist had no effect on water intake, the DRD2 antagonist slightly reduced thirst behaviors (Figure 3B).

Results After both microarray and GSEA provided strong evidence to demonstrate the regulation of DARPP-32 in the hypothalamus of sodium depleted animals, further attention was directed towards DARPP-32 through immunohistochemistry. Immuno-labeling was not performed on the tissue from gratified animals, since a ten-minute time scale is too short to allow for changes in protein expression.

DARPP-32 expression was detected in the supraoptic nucleus and supra-chiasmatic nucleus, although sodiumdepleted and control conditions did not show significantly different labeling patterns for these two nuclei. However, upregulation of DARPP-32 in sodium-depleted animals was detected in the lateral hypothalamus as well as in the para- and periventricular nuclei (Figure 4B). Through utilization of double immuno-labeling, more specific analysis was conducted on the lateral hypothalamus, showing that neurons labeled for DARPP-32 also co-expressed orexin.

Thus, in sodium-deprived animals, DARPP-32 exhibited specific up-regulation in the orexinergic sub-population of lateral hypothalamic neurons, which play a key role in behaviors of motivation and reward (Figure 5).

Additionally, triple labeling studies were completed in order to examine the regulation of the immediate early gene Arc (activity-regulated cytoskeletal-associated protein), which demonstrated hypothalamic up-regulation in sodium deprived animals, as gathered from the microarray studies. Arc has been shown to function as a master regulator of neuronal plasticity, both in adaptive responses Vol 1 Issue 1 | Fall 2011 | neurogenesisjournal.com | 17

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to physiological stresses and in maladaptive stresses to addictive substances (Bramham et al., 2010). Implicated not only in processes of memory but also presenting ties to stress and drugs of abuse (Fumagalli et al., 2009), a single session of intravenous cocaine self-administration, caused an increase of Arc expression in the medial prefrontal cortex. Concurrent with the finding of hypothalamic Arc regulation in sodium deprived animals, by utilizing triple immuno-labeling, the ARC protein was detected in the orexinergic population of neurons in the lateral hypothalamus that also express DARPP-32 (Figure 6A,B). Based upon the observed co-expression patterns, ARC function was hypothesized to be preparation of lateral hypothalamic neurons for subsequent participation in reward circuits upon sodium depletion, leading to gratification behaviors. Regulated expression of Arc led to consideration of whether gene sets associated with overall neural activity may be associated with these processes. These gene sets, however, were enriched in neither separate conditions of sodium deprivation nor in combination. This finding suggests that sodium-depletion-induced hypothalamic regulation of sodium appetite may not function as part of global neuronal activity processes, but rather along with more specific neural plasticity mechanisms related to instinctual behaviors.

After the aforementioned behavioral and knock-out studies indicated that DRD1 signaling plays a significant role in sodium appetite, and not thirst for water, among sodium deprived animals, DRD1 protein expression was investigated. Brain slices from sodium-deprived and control mice were double-labeled for DRD1 and orexin in order to interrogate the possibility of DRD1 receptors functioning in the orexinergic population of the lateral hypothalamus. Satisfactory neuronal labeling was achieved in select cases (Figure 7). In general, however, definitive labeling of neurons and processes was not obvious, leaving unanswered the question of whether DRD1 receptors in the LH are expressed on orexinergic neurons or not.

In order to view exact placement of the cannula as well as the neural area affected by the drug administration, a fluorescently-labeled dextran tracer was injected, before the animals were sacrificed, to mark the injection site. For animals that did not show robust sodium appetite after injection of aCSF, attempts were made to investigate the possibility of surrounding damaged neurons, which would lead to reduction in the expected gratification behavior.

Brain slices were labeled with Fluoro-Jade b, a marker of degenerating neurons (Schmued, 2000). The staining protocol was used in accordance with that given by Millipore. Even though the staining methodology appeared to have been properly implemented (Figure 8), the lack of definitive results did not allow for conclusions to be drawn concerning the extent of neuronal damage and possible implications for behavior as caused by the cannula.

However, since certain animals did not show the expected behavior in response to targeted aCSF injection, it is likely that instead of impairing neurons’ survival in this area, the 18 | neurogenesisjournal.com | Fall 2011 | Vol 1 Issue 1

Articles cannula actually destroyed the tissue, thus inducing a lesion akin to those induced in the 1964 study by Wolf.

Discussion Sodium appetite is an instinctive drive leading to specific and evolutionarily highly advantageous behavioral patterns. Along with other innate drives, many of which are controlled by the hypothalamus, such as hunger and sexual arousal, sodium appetite exemplifies a tightly regulated neural system, integrating input information concerning the state of sodium depletion, causing a highly

Figure 4: DARPP-32 labeling in the hypothalamus (A) This top panel shows an atlas representation of the pertinent nuclei in the hypothalamus that were investigated in terms of DARPP-32 expression, as well as labeling of a few anatomical markers.(B) In analysis of the DARPP-32 expression in the hypothalami of sodium depleted animals versus controls, there seemed to be no appreciable difference in the labeling pattern between these groups in either the SCN or SON. However, sodium depleted animals showed appreciable up-regulation of DARPP-32 in the PeVN.

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Figure 5: DARPP-32 up-regulation in the orexinergic neurons of the LH In sodium-deprived animals, DARPP-32 seems to show specific up-regulation in the orexinergic sub-population of lateral hypothalamic neurons, which have been shown to play a key role in behaviors of motivation and reward.

aroused state and a specific intention, driving the animal to ingest salt.

This study contributes to the understanding of the neural circuitry responsible for sodium appetite. However, the findings presented within this paper must be integrated

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with additional evidence underlying the physiological basis of sodium appetite in order to create a complete concept of the genesis of and response to sodium appetite. Beyond the neural regulation of sodium appetite, the added understanding of other physiological systems in the maintenance and correction of fluid homeostasis may further complicate the study of hypothalamic gene regulation of sodium appetite. The high survival value of sodium appetite necessitated an evolutionarily adaptive process in which selection processes in each animal dictated the eventual neural regulation and organization managing the process of sodium appetite. Different factors may provide varying influences to the genesis of sodium appetite among various species of animals; different selection pressures, perhaps depending upon environment or lifestyle, may have exerted varying levels of influence upon different animals during their respective evolution of this critical instinct.

The gene changes demonstrated in this study most likely participate in the generation of a state of arousal, causing the animal to seek sodium. However, this paper does not delve into the gene regulation involved with gratification or the time course of protein production as influenced by changes in gene expression. Additionally, gene regulation Figure 6: Up-regulation of DARPP-32 and ARC in the orexinergic neurons of the LH in sodium depleted rats (A)Triple labeling studies were completed in order to examine the regulation of the immediate early gene Arc (activity-regulated cytoskeletalassociated protein), which demonstrated hypothalamic up-regulation in sodium deprived animals, as gathered from the microarray studies. Arc has been shown to function as a master regulator of neuronal plasticity, both in adaptive responses to physiological stresses in maladaptive stresses to addictive substances. Concurrent with our finding of hypothalamic Arc regulation in sodium deprived animals, by utilizing triple immuno-labeling, the ARC protein was detected in the orexinergic population of neurons in the lateral hypothalamus that also express DARPP-32.

(B) This panel contains confocal micrographs of LH neurons, showing some subcellular localization.

(C) Densitometic analysis from control and sodium depleted animals (n=3) indicates that both DARPP-32 and ARC are regulated in the LH. (D)Further densitometic analysis shows that DARPP-32 and ARC demonstrate total co-localization in the LH, whereas DARPP-32 and orexin show about 87% co-expression.

These thresholds are set based upon expression averages from control animals.

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Figure 7: DRD1 labeling in the orexinergic neurons of the hypothalamus While LH tissue from one sodium deprived animal demonstrated possible co-expression of DRD1 and orexin, more extensive studies are needed in order to extract the true meaning of these results.

of other physiological functions implicated in the process of sodium depletion and gratification, such as blood pressure and renal function, although not analyzed during these experiments, likely exert reciprocal influence with the neural regulation. Examination of comprehensive systemic gene regulation involved in sodium appetite would provide a more conclusive picture of the time course and changes in protein function.

Although the complete general mechanism underlying gene regulation of sodium appetite remains to be fully disclosed, our results offer a novel introduction, providing a starting point and foundation of hypothalamic gene regulation of sodium appetite, perhaps extending to instinctive behaviors in general.

Remarkable findings include the rapid gene regulation changes during gratification as well as the concurrent loss of sodium appetite occurring before possible systemic equilibrium, likely resulting from a behavioral state of gratified instinctive need. This rapid loss of gene regulation presumably occurs at the mRNA level. The underlying gene-regulatory mechanism controlling HT instinctive gratification pathways remains unknown; however, there is possibility that microRNAs (miRNAs) are tagging the regulated mRNAs for rapid degradation. miRNAs are endogenous, non-coding small RNAs of about 22 nucleotides in length that serve as regulators of gene expression by inducing mRNA cleavage and/or translational repression (Guo, 2010). miRNA have emerged as key post-transcriptional regulators of gene expression, predicted to control activity of about 50% of protein-coding genes in mammals and are thought to possess a role in stress responses (Krol, 2010).

In order to begin preparation for future investigation of miRNA, 8um fresh frozen tissue slices have already prepared from three groups of rats – sodium depleted, gratified, and control. Laser Capture Microdissection will be utilized in order to achieve precise dissection of the brain areas of interest, including the lateral hypothalamus and periventricular nucleus. miRNA extraction and analysis from these tissues will be achieved by using a miRNA PCR array kit, which will identify the most abundant miRNA present during each of these conditions.

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Figure 8: Fluoro-Jade and cannula placement labeling in rats microinjected with DRD1 antagonist The left panel shows the placement of the cannula in the LH, as indicated by injection of a fluorescently-labeled dextran tracer prior to euthanasia.

The right micrograph indicates labeling with Fluoro-Jade b, which is a marker of degenerating neurons. Even though the staining methodology appeared to have been properly implemented, the lack of definitive results did not allow for conclusions to be drawn concerning the extent of neuronal damage and possible implications for behavior as caused by the cannula.

However, since certain animals did not show the expected behavior in response to targeted aCSF injection, perhaps instead of damaging neurons of the lateral hypothalamus, the cannula actually killed the surrounding cells, thereby unable to be labeled as degenerated by the Fluoro-Jade.

thalamus as a critical locus underlying the neural response to sodium appetite, providing signaling for motivational behaviors intended to correct the dysequilibrium. Further neuroanatomical specificity was achieved through immunohistochemical studies, highlighting the changes in DARPP-32 and ARC expression in the lateral hypothalamus, lending additional credence to previous studies (Cason et al., 2010;Aston-Jones et al., 2009; Harris et al., 2005) that have provided strong evidence of the role of the lateral hypothalamus and orexinergic neurons in motivational behaviors and reward. The role of the lateral hypothalamus in sodium appetite was suggested almost half a century ago in 1964 in a lesioning study (Wolf, 1964), and behavioral experiments have continued to identify the lateral hypothalamus as component of motivational processes (Hoebel, 1989). The experiments presented here identify a specific and behaviorally significant functioning of dopamine receptor signaling in sodium appetite. Future studies will need to address the actions of dopamine in coordination with their cognate receptors and the neuronal subtypes that express them as well as modulatory influence by intracellular signaling such as affected by molecules such as DARPP-32.

These findings, concerning hypothalamic upregulation of DARPP-32 as well as the participation of genes contained within gene sets previously linked to drugs of abuse, provide a link between instinctive behaviors and addiction.

Sodium appetite represents an instinctive need, and brain pathways regulating these processes have been evolving for millions of years. However, as drugs of abuse and the processes of addiction have only appeared within recent history, the data presented within this study suggests that drugs of abuse have latched onto this previously established circuitry underlying powerful survival mechanisms.

Although this research focused primarily on the effect of sodium depletion on the hypothalamic up-regulation of

Articles DARPP-32, a widely investigated molecule in studies of addiction, this work provides a foundation to address the neural circuitry involved in instinctive needs. These findings permit future studies to interrogate the neural circuits activated during the different stages of sodium appetite and more broadly for all instinctive needs, including conscious sensing of the need, followed by specific and robust motivated behavior, with subsequent cessation of gratification – commensurate to need. Further insight into the molecular components of the circuitry, as well as brain regions involved in connections to the lateral hypothalamus will impart additional evidence linking addiction circuitry to primordial instinctive behaviors.

Material and Methods Animals Animal studies were all conducted in accordance with the regulations as set by the animal care and use committees at both Duke University and collaborating institutions. Only trained scientists performed the animal handling. Post-mortem, the author performed all dissections to remove the animal brains from the cranium as well as all embedding and subsequent histological procedures.

Sodium deprivation Each group—furosemide injected, ACTH treated, and control—consisted of 5-6 mice. Initially, individually housed mice (C57/B16, male) were offered water, 0.3 M NaCl and low sodium food (0.02%). Basic control data of body weight as well as intake of food, water, and NaCl were measured for one week, at which time the process of sodium deprivation commenced with the removal of the sodium drinking solution from the mice cages. The mice were intraperitoneally injected for two days with 1.2 mg furosemide and were euthanized on the third day. The tissue was collected into liquid nitrogen, with the hypothalamus eventually being removed and the rest of the brain serving as control. Control mice maintained a diet composed of 0.5% NaCl. For immunohistochemical studies, control rats were compared against furosemide-induced sodium depletion rats, 3-4 animals each per group. For rats (male, SpragueDawley, mean: 300 g; 12 weeks of age), housed individually, the process of sodium deprivation began with offering them only distilled water and low sodium food (0.02%, Harlan, TD90.228, Harlan, Madison, WI) for one week.

In the in middle of that week on days 3-7, the animals were intraperitoneally injected with 5 mg/kg/d furosimide (Aventis Pharma Germany). Functioning as a diuretic, this compound removed all excess salt from the animal bodies, allowing for comprehensive sodium depletion. After the rats were euthanized, the brain was quickly dissected from the cranium, and cut at the level of the optic chiasm. The posterior and anterior halves were separately embedded in blocks with OTC compound on dry ice.

ACTH infusion

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As for animals sodium depleted via the ACTH method, female C57/B16 mice were given water, 0.005 M NaCl, as well as ACTH delivered via a mini-osmotic pump at 2.8 μg/d for 12 days. Whereas the control animals averaged intake of 1.6 mL/day of the 0.005 M NaCl solution, on the last 4 days of ACTH infusion, the mice drank on average 9.3 mL/day.

Gratification In the gratification studies, sodium depleted mice, after 2 days of furosemide injections, were permitted on the third day to drink 0.3 M NaCl for 10 minutes and were subsequently sacrificed. For mice treated with ACTH, the same protocol was followed except that the 0.3 M NaCl solution was available throughout the duration of the ACTH administration.

Immunohistochemistry Rat brains (sodium depleted vs. controls) were fixed under either of the following conditions: by transcardial perfusion after euthanasia with 2% paraformaldehyde followed by 50 μm vibratome sectioning or by saline perfusion, in which fresh tissue was embedded into blocks with OTC compound on dry ice for subsequent 25 μm cyrostat sectioning. Vibratome sections were collected in a bath of 1x PBS and then, using skip section methodology, were transferred to a 6-well plate in which they underwent the subsequently outlined detailed staining protocol. Twentyfive μm fresh-frozen sectioning was performed in a cyrostat at -22°C, with sections transferred directly to glass microscope slides. In order to maintain the quality of the aforementioned tissue, fixed sections were stored at 4°C, while fresh-frozen sections were stored at -80°C. Both vibratome and fresh-frozen sections were labeled with a mouse monoclonal antibody as supplied by Dr. Paul Greengard, and followed by detection with Alexa-488 anti-mouse secondary. Further amplification was achieved for double and triple labeled sections; after primary antibody incubation, instead of solely using fluorescent secondary antibodies, higher-specificity detection was achieved by utilizing a complex of secondary antibodies conjugated to biotin molecules plus streptaviden. For double labeling of both vibratome and fresh-frozen sections, the tissue was labeled with mouse anti-DARPP-32 in addition to goat anti-orexin antibody (orexin A antibody, SantaCruz Biotechnology sc-8070). Detection of antiDARPP-32 was completed more directly with subsequent application of anti-mouse-Alexa-488 secondary antibody, whereas detection of anti-orexin utilized a system of anti-rabbit biotin followed by streptavidin-Alexa-595 (Invitrogen-Molecular Probes). In order to achieve successful triple labeling, sections were incubated with mouse anti-DARPP-32, goat anti-orexin, and rabbit anti-ARC (SantaCruz Biotechnology), accompanied by secondary detection with anti-mouse-Alexa-488, anti-goat biotin plus Streptavidin-595, and anti-rabbit-Alexa-360. After completion of antibody staining, the fluorescent labeling was viewed using both fluorescent microscopy (Olympus Vol 1 Issue 1 | Fall 2011 | neurogenesisjournal.com | 21

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BX61 microscope) and confocal imaging (Zeiss LSM710).

After the slides were removed from the -80°C freezer, they were rinsed with 1x PBS, outlined with a barrier pen in order to form a hydrophobic border, fixed with 2% PFA for 2 minutes, and subsequently washed three times with washing buffer (0.05% Tween 20 in 1x PBS) for 5 minutes each. Next, they blocked for two hours at room temperature in a solution of 5% normal goat serum and 0.1% Triton X in 1x PBS. During primary antibody incubation, the slices were covered in a solution of anti-DARPP-32 (1:12,000), anti-orexin (1:1000), and anti-Arc (1:1000) in the blocking solution at 4°C overnight. Excess primary antibody was removed by applying washing buffer to the slides three times for five minutes each again. Next, the slices were covered in the secondary antibody incubation solution, composed of anti-mouse-Alexa-488 (1:500), anti-goat biotin (1:250), and anti-rabbit-Alexa-360 (1:100).

After a final round of washing, a blocking solution with Streptavidin-595 (1:500) was added in order to allow detection of the goat antibody. Coverslips were mounted onto the slides using fluoromount and sealed with nail polish in order to enhance the duration of tissue quality.

Ahmed SH, Letjens R, van der Stan LD, Lekic D, Romano-Spica V, Morales M, Koob GF, Repunte-Canonigo V, Sanna PP. Gene expression evidence for remodeling of lateral hypothalamic circuitry in cocaine addiction. PNAS, 102, 11533-11538 (2005).

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Neuroscience on the nature of consciousness Hannah Gold1 Duke University, Durham, North Carolina, 27708 Correspondence should be addressed to Hannah Gold (hannah.gold@duke.edu) 1

The idea that the mind is related to the brain is commonly accepted by philosophers and neuroscientists, but the nature of that relationship remains puzzling. Current research seeks to explain consciousness, an essential component of the mind, through concrete, observable findings of neuroscience. Because it is difficult to directly assess consciousness through experimentation, researchers look for correlated processes to serve as markers that can be experimentally manipulated. Two potential markers of consciousness that might provide useful insight into the relationship between the brain and the mind are attention and volition.

Intuitively, the idea that consciousness can be explained by attention is attractive. For instance, sentiments like, “the driver wasn’t paying attention so he didn’t even realize the light had turned red,” associate attention with consciousness. Of course the driver saw the color change (he is not blind), but he didn’t “realize” that it changed—the sensory information didn’t reach his conscious processing, and this is attributed to a lack of attention. In fact, the connection between attention and consciousness goes beyond folk psychology. Neuroscientists have proposed that attention acts as the gatekeeper of consciousness, preferentially weighting different aspects of stimuli so that only the most relevant information reaches consciousness.

Attentional moderation of neuronal responses to stimuli is seen on fMRI images as early in the visual processing pathway as the LGN of the thalamus (before the information even reaches the cortex, the part of the brain associated with consciousness) (O’Connor, 2002). Because of the influences of attention, a “purely sensory representation” of stimuli does not ever exist in the cortex (Treue, 2003), and thus we are never conscious of our actual surroundings.

Instead we perceive a version pared down to only the most relevant aspects of our surroundings.

But not everyone accepts this explanation of consciousness. First of all, attention does not cause a previously unconscious event to become more conscious. Careful experimental design can separate the effects of conscious and unconscious primes and then show that attention does not make effects of unconscious primes more like the effects of conscious ones. Instead, attention exaggerates the effects of the unconscious stimuli, making them in a way more unconscious as opposed to more conscious (Sumner 2006). Thus, the effects of attending to a stimulus are actually quite distinct from the effects of becoming more conscious of a stimulus. Another piece of neuroscience

which contradicts the “consciousness is attention” theory is the ability of consciousness and attention to exist independently. Since a subject can attend to a stimulus without being conscious of it (Naccache, 2002) or visa versa (Reddy, 2004), then consciousness and attention must be separate mechanisms.

However, these attacks on the original intuition that consciousness is closely linked to attention have one main flaw, and it is a theoretical one. The studies that claim to demonstrate consciousness without attention assume that attention is an all-or-nothing function, but really it seems that the supposedly “unattended stimulus” could simply be the less attended stimulus. The mistake of making allor-nothing, existence-or-nonexistence declarations when trying to draw conclusions from data is a common one in cognitive neuroscience. Of course it is necessary to make some category discriminations in neuroscience (conscious vs. unconscious, attended vs. unattended) in order to understand the varied functions of the brain, but the macroscopic picture must always be kept in view. The brain is not made of independent processes that simply come together to produce the mind; it is a conglomeration of specialized circuits and systems that not only dynamically interact but also are constituent parts of one another. Such philosophical insight could benefit science when drawing conclusions from experimental data.

The second window into consciousness that seems useful is volition. The intuition is that voluntary actions and the motor patterns they entail require consciousness, whereas automatic behavior is unconsciously controlled.

By traditional definitions, voluntary actions are flexible and can be influenced by context whereas automatic motor patterns are inflexible and impervious to outside influences. Such a definite distinction between voluntary and involuntary behavior supports a similarly strict division between consciousness and unconsciousness.

As with the story of attention and consciousness, it is more complicated than that; for instance, recent neuroscience studies have presented evidence that voluntary action can be partly explained by unconscious events. For instance, if a subject views a graspable object, the afforded motor plans for reaching out and grabbing the object are partially activated. This is evidenced by the fact that the handed-ness of the object affects the reaction time for a subject to press a button with the corresponding hand. If the object (a mug for instance) is right-handed, then the reaction time for pressing a button with the right hand is Vol 1 Issue 1 | Fall 2011 | neurogenesisjournal.com | 23

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faster as opposed to pressing a button with the left hand.

This indicates that somehow the right hand motor response is partially activated before volition could possibly take effect (Tucker, 1998). The motion to pick up the mug was activated unconsciously before the subject consciously decided. The conclusion of such studies is that volition may just be an illusion, because our actions may be initiated by unconscious mental processes long before we become aware of the intention to act (Soon, 2008).

A second strike against using volition as a marker of consciousness complements the “voluntary action as unconscious” studies by showing the opposite situation, “automatic action as conscious.” What neuroscientists call “conditional automaticity,” is evidence that involuntary behavior is not so independent of consciousness as suggested by the volition-is-conscious/automaticity-is-unconscious divide theory. For example, conditional automaticity describes circumstances when automatic motor activation is dependent on context. Within the context of driving a car, the sudden appearance of a stimulus (a deer) causes us to enact an automatic foot motion to depress the brakes. This response is obviously dependent on the context—if we aren’t driving a car, we don’t stomp on nonexistent brakes when we see a deer dash in front of us. Controlled studies of conditional automaticity (Naccache, 2002) make the distinction between volitional and automatic behavior distinction fuzzier, which brings the conscious versus unconscious distinction also into question.

These attacks against the traditional concept of volition also make a powerful statement about consciousness; if volition is not as definitive as once assumed (or perhaps does not even exist at all), then perhaps consciousness isn’t (or doesn’t!) either. First of all, the studies cited encourage a more complex view of volition. Instead of being the white knight of consciousness, volition is actually made of unconsciously activated motor patterns. Conscious volition might just arise when there is competition between afforded action plans that must be refereed. It is unlikely that a certain number of possible action plans exists as a cutoff beyond which conscious (volitional) mediation is needed, and it is more probable that consciousness and volition are graded functions which can be engaged at different levels based on how much conflict resolution needs to be done between competing motor plans. What this means is that volition and automaticity are on a continuum, which suggests that maybe consciousness and unconsciousness are as well. The second, more drastic implication is that consciousness is entirely impotent. If the causal power of volition is only illusory, then maybe consciousness does not act upon the physical world either. Here is the place where neuroscience and philosophy become more deeply intertwined.

If neuroscience is careful to keep in mind the arbitrary nature of its category discriminations, it is a useful tool for investigating the mind. Results from investigating attention and volition both seem to support an epiphenomenalist view of consciousness, which posits that mental states 24 | neurogenesisjournal.com | Fall 2011 | Vol 1 Issue 1

Letters do not have any effect on physical states and are instead merely by-products of other processes. The results expand the role of unconscious processing, showing that phenomena we originally assumed had to be consciously controlled could in fact be accomplished unconsciously. Consciousness may just be along for the ride; it may be merely the result of subconscious, automatic and physical processing and have no effects upon those physical processes. Studying neuroscience in cooperation with philosophy may be a useful way to approach the mystery of the human mind and illuminate the answers to these critical questions.

Laberge D. (1995). Attentional Processing: The brain’s art of mindfulness.

Cambridge, MA: Harvard University Press.

Mack, A. & Rock, I. (1998). Inattentional Blindness. Cambridge, MA: MIT Press.

Naccache L, Blandin E, Dehaene S. (2002). Unconscious masked priming depends on temporal attention. Psychological Science 13, 416-424.

O’Connor, D.H., Fukui, M.M., Pinsk, M.A., Kastner, S. (2002). Attention modulates responses in the human lateral geniculate nucleus. Nature Neuroscience. 5, 1203-1209.

Reddy, L., Wilken, P., Koch, C. (2004). Face-gender discrimination is possible in the near-absence of attention. Journal of Vision. 4 (2). 106-118.

Soon, C., Brass, M., Hans-Jochen, H., Haynes, J. (2008). Unconscious determinants of free decision in the human brain. Nature Neuroscience.

11, 543-545.

Sumner, P., Tsai, P., Yu, K., Nachev, P. (2006) Attentional modulation of sensorimotor processes in the absense of perceptual awareness. Proceedings of the National Academy of Sciences of the United States. 103 (27), 10620-10525.

Sumner, P., Husain, M. (2008). At the edge of consciousness: Automatic motor activation and voluntary control. The Neuroscientist. 14, 474-486.

Treue, S. (2003). Visual attention: the where, what, how and why of saliency.

Current Opinions in Neurobiology, 13, 428-432.

Tucker, M., Ellis, R. (1998). Action priming by briefly presented objects.

Acta Physchologica. 116, 185-203.

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Free will: Not worth giving up on Ryan Bortholomew1 Duke University, Durham, North Carolina 27708 Correspondence should be addressed to Ryan Bartholomew (ryan.bartholomew@duke.edu) 1

ABSTRACT: The following paper provides reason to believe that determinism causes irreparable damage to free will, and with it our way of life. Compatibilism, while good intentioned, fails to successfully remedy the damage wrought upon free will by determinism. However, hope for free will remains, as at this point in time indeterminism remains a viable possibility, as does conscious causation. Even if indeterminism turns out undeniably false, for the sake of maintaining the wellbeing of humanity, belief in free will must continue.

Consider the following situation: Fred has his hands at the steering wheel of his car. He is driving down a road, believing himself to be in control of the car’s trajectory.

The car, in fact, sits upon rails, preventing it from following but a single path. Farther down the road, the rails happen to intersect with a sandbox where children are playing.

The moving car, following the determined route, speeds through the sandbox and kills the children. Fred, under the impression that he had determined the car’s route, feels wholly responsible for the death of the children. The townspeople, who also held Fred responsible, execute him as retribution for his despicable act. A follow up investigation, however, reveals the presence of the rails; the townspeople attain good reason to believe that Fred did not know of the existence of the rails and was innocent.

The townspeople realize that they have committed an abhorrent injustice, executing a poor man who simply found himself in the unlucky seat of a rickety car determined to go down an ill-fated path. Those who believe in the existence of determinism must accept that people have no ultimate control over the source of their behavior, and consequently, no ultimate control over the behavior itself. The necessity of alternative possibilities required for an agent to have the power to do otherwise (i.e. free will) cannot be satisfied in a determined world. The deterministic laws of nature dictate that, given a certain set of conditions A, outcome B will result 100% of the time. Therefore, if a person’s decision-making process must also adhere to deterministic laws, then a certain set of conditions would always result in the same choice made if the exact moment in time was rewound and repeated an infinite number of times. With science providing “continuing support for deterministic thinking about human behavior” (Kane, 2002), abandoning our traditional notion of libertarian free will may, unfortunately, eventually be in order.

Classical compatibilism attempts to reconcile free will and determinism and results in an inadequate form of will unworthy of having the word “free” precede it. After looking past the smoke and mirrors, compatibilism provides only the ability to will what determinism dictates we will.

The content of the will we attribute to the person, but “being the person one is and having the desires and beliefs one has, are ultimately something one cannot control”

(Kane, 2002). What we will, then, is simply an unfolding of what we cannot control. If we do not have control at the foundational level of our actions—the foundation being who we are as a person—then we cannot suddenly attain control at the local level of our action, as it rests upon the uncontrolled foundation. As a result of our intuitions and subjective experience, it seems that we have control. For this reason, we deeply attribute our actions to ourselves.

The existence of determinism however would reveal such responsibility to be no more than illusory.

When advocates for determinism state that, on a macroscopic level, everything is determined, what they are really saying is that it seems or could be that everything is determined. For example, let us say that Jack and Jill both expose themselves to chicken pox, but only Jack falls ill.

The naïve indeterminist could exclaim that since only Jack fell ill, determinism loses credibility. The determinist would quickly respond “that there were hidden physical variables at work in the situation (e.g., factors having to do with the physical well-being of Jack and Jill, or the duration of their exposures, [etc.]) that determined that Jack would contract the disease and Jill would not” (Balaguer, 2009). However, unless the determinist can discern all the initial conditions and hidden variables and then prove that a certain macrolevel outcome to be determined, the determinist cannot push his views off as truth. For all we know, “macro-level events - e.g., coin tosses, quantum-measurement events, decisions, and so on - might be neither determined nor virtually determined” (Balaguer, 2009).

The determinist may argue that the brain functions deterministically. However, “current neuroscientific theory treats a number of different neural processes probabilistically” (Balaguer, 2009). Release of transmitter at a presynaptic terminal does not occur every time an action potential arrives and spontaneous release can even occur even in the absence of an action potential (Dayan and Abbot, 2001). Dayan, an author of one of the aforementioned neuroscience textbooks, says that “people would argue that there are good thermal reasons to think that [the opening and closing of ion channels] is truly random” (Balageur, 2009). Of course we must concede that by treating neural processes as random, the neuroscientist does not commit himself to indeterminism: “it could be that there are unVol 1 Issue 1 | Fall 2011 | neurogenesisjournal.com | 25

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derlying deterministic physical explanations of the phenomena” (Balaguer, 2009). However, the determinist must concede that the neuroscientist does not commit himself to determinism either.

Libertarian free will may not exist. However, the lack of definitive evidence for macro-level determinism, in conjunction with current neuroscientific theory, suggests that the possibility for its existence remains open. For the time being, no responsible philosopher can say that without a doubt we irrevocably live, for all practical purposes, in a determined universe. Could the stochastic release of neurotransmitters in the absence of an action potential be the activity of our will acting in the absence of antecedent causes? Perhaps neurotransmitters fail to release in the presence of an action potential as a result of our free will acting to override that which the antecedent causes dictate we will. Or it may be that a completely different explanation awaits discovery for the stochastic nature of some neural processes. As it currently stands, humanity has no good reason to throw the concept of free will by the wayside.

Footnotes Macro-level Determinism: The philosophical view that the universe, on a macroscopic level, is completely governed by casual laws which result in but only one possible outcome in any situation.

Robert Kane presents the traditional conception of having libertarian free will as when (a) it is ‘up’ to us what we choose from an array of alternative possibilities and (b) the origin or source of our choices and actions is in us and not in anyone or anything else over which we have no control. (Kane, 2002) Classical compatibilism provides “the power to do otherwise” (a) needed for free will through conditional analysis. The individual could have chosen otherwise if the individual wanted otherwise, providing a conditional alternate possibility (Kane, 2002, p.11). To crudely summarize, freedom of will, from the view of classic compatibilism, only requires that there be a lack of restraints on the individual’s ability to do as he desires, with the content of the desire being determined by antecedent causes.

Balaguer, M. (2009). Why there are no good arguments for any interesting version of determinism.

Kane, R. (2002). The Oxford Handbook of Free Will. New York: Oxford University Press.

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Effects of resting state on perceptual skill learning Snigdha Peddireddy1 Duke University, Durham, North Carolina, 27708 Correspondence should be addressed to Snigdha Peddireddy (snigdha.peddireddy@duke.edu) 1

Previous studies have shown that a short nap immediately following a visual discrimination task leads to subsequent improvement in both behavioral and neural performances in the same task. However, little is known about the processes that occur during rest that lead to the observed improvement. One possibility is a neural phenomenon known as replay, which is defined as a reactivation of the pattern of brain activity evoked during a task. Because replay may strengthen local network functional connectivity modified during the task, it was hypothesized that this phenomenon results in the observed offline improvement. A positive correlation between the amount of replay during the rest period and improvement in performance in the following task was thus predicted. Recordings were taken from a region of the extrastriate visual cortex (V4) from an awake, behaving rhesus macaque during an image orientation discrimination task and interleaved 20-minute rest periods. The recordings were gathered using 16-contact laminar multielectrodes advanced with a computer-controlled NAN microdrive. The experimental paradigm consisted of an initial rest period lasting twenty minutes that was used to record baseline neural activity followed by the image discrimination task during which the monkey differentiated between images of same or different orientation. The monkey subsequently underwent a second rest period of equivalent length in which the amount of replay was measured. Replay was measured by assessing the probability that cells coactivated during the task continued to be reactivated together during the second as compared to the first rest period. This demonstrates modifications in network functional connectivity by the task. After another discrimination task, improvements in behavioral and neural performances from the initial task were assessed using psychophysics curves and differences in neuronal d’ values. The d’ value was used to determine how well neurons were able to discriminate between two stimuli (in this case, two differently oriented images). Data from nine sessions suggested that an increased amount of rest and, in turn, replay was in fact positively correlated with task performance. This research may aid the development of drug treatments or noninvasive therapies to facilitate memory consolidation in Alzheimer’s Disease or insomnia patients faced with memory impairment.

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Temporal and spatial constraints of the cross-modal spread of attention Helen Zhang1, Sarah Donohue2, Marty Woldorff2 Duke University, Durham, North Carolina 27708 Duke University Center for Cognitive Neuroscience, Durham, North Carolina 27708 Correspondence should be addressed to Helen Zhang (helen.zhang@duke.edu) 1 2

ABSTRACT: The neural and perceptual integration of multisensory stimuli is influenced by the spatial and temporal proximity of stimuli as well as by attention. In particular, the temporal linking of stimuli occurs for auditory and visual events across a relatively wide (+/- 150 ms) temporal window of integration, while the spatial linking of multisensory stimuli seems to occur only for very closely simultaneous events. Cross-modal spread of attention occurs when auditory and visual events are simultaneous and when the auditory tone is delayed by 100 ms, but not when the tone is delayed by 300 ms (outside the window of integration). It is unknown whether, following similar temporal constraints, a similar spread of attention occurs when an unattended stimulus is presented near-synchronously and prior to an attended stimulus. The present study compared neural activity elicited by synchronous and near-synchronous unattended auditory stimuli presented before attended visual stimuli, both within and outside the temporal window of integration. Using electroencephalography (EEG), behavioral performance and high-density (64 channel) Event-Related Potentials (ERPs) were measured in fifteen participants, who selectively attended to one of two lateralized visual-stimulus streams while task-irrelevant tones were presented centrally simultaneously, 100 ms before, and 300 ms before the attended visual stimulus. Analyses of brain activity revealed a cross-modal spread of attention still within the classic temporal window of integration— reflected by an enhanced frontal-central negativity elicited by presentation of a central tone simultaneously with and 100 ms before an attended visual stimulus.

Introduction The successful integration of multisensory information is essential for even the simplest daily behaviors, involving the interaction of information from different sensory modalities, such as visual and auditory, and their combination into a unified sensory perception. The processes of multisensory integration are guided by both temporal and spatial principles (Stein & Meredith, 1993; Stein & Stanford, 2008; Wallace et al., 2004). In general, stimuli must have sufficient temporal and spatial proximity in order to be integrated into a single object (Lewald, Ehrenstein & Guski, 2001; Lewald & Guski, 2003; Meredith, Nemitz & Stein, 1987; Stone et al., 2001; Zampini et al., 2005; Senkowski et al., 2007). In addition to the grouping of information from multiple sensory modalities, stimulus processing is also guided by selective attention. Simultaneous multisensory stimuli, for example, can attract attention more easily than those that occur separately in time, suggesting that attention orients more easily towards multisensory rather than unisensory objects or events (Van der Burg, Oliviers, Bronkhorst, & Theeuwes, 2008; Van der Burg, Oliviers, Bronkhorst, & Theeuwes, 2009). The processes of multisensory integration have also been demonstrated to be modulated and enhanced by attention, as reflected by greater brain activity in response to attended multisensory events (Talsma & Woldorff, 2005; Talsma et al., 2010).

Attention is a crucial cognitive function that allows for the continuous, dynamic selection of stimuli from the environment. Greater neural activity seen in neurophysiolog28 | neurogenesisjournal.com | Fall 2011 | Vol 1 Issue 1

ical measures such as EEG and fMRI, as well as reflected by behavioral measures, such as faster reaction time and increased discrimination accuracy, reflect the resulting enhanced processing of attended stimuli (Hillyard & AnlloVentro, 1998; Brefczynski & DeYoe, 1999; Posner & Petersen, 1990). Additionally, attention can be object-based, spreading from one component of an object to enhance processing of other components of the same object. This spread of attention has been demonstrated both behaviorally and neurophysiologically to occur unimodally, between components of the same modality (Egly et al., 1994; Martinez et al., 2006; O’Craven, Downing & Kanwisher, 1999; Schoenfeld et al., 2003) and, more recently, crossmodally, between components of different modalities, as well (Busse et al., 2005; Molholm, Martinez, Shpaner, & Foxe, 2007; Zimmer et al., 2010a, 2010b, Donohue et al., in press). Studies examining the cross-modal spread of attention have found that this effect generally follows the same temporal and spatial principles that apply to multisensory integration (Busse et al., 2005; Donohue et al., in press). This study aims to further define the temporal and spatial constraints of multisensory integration and crossmodal spread of attention, and to identify the ways that these processes are modulated by attention.

Temporal and spatial linking of multisensory stimulus components The temporal and spatial linking processes of stimulus components, important for the integration of sensory information from multiple modalities, are gov-

Articles erned by several general principles (Stein & Stanford, 2008; Wallace et al., 2004). First, stimuli need to occur fairly closely in time for effective sensory integration to occur, with a typical window of time for the integration of visual and auditory stimuli reported to be around 150 ms—as demonstrated through both behavioral and neurophysiological measures (Meredith, Nemitz & Stein, 1987; Stone et al., 2001; Zampini, Guest, Shore, & Spence, 2005; Senkowski, Talsma, Grigutsch, Herrmann, & Woldorff, 2007). Near and beyond the window of temporal integration, the stimulus onset asynchrony (SOA) between each component is inversely related to the probability that each component will be integrated into and perceived as one source (Lewald, Ehrenstein & Guski, 2001; Lewald & Guski, 2003).

The stimulus components also need to occur with sufficient spatial proximity in order for multisensory integration to occur. Behaviorally, cross-modal stimuli are perceived as occurring simultaneously more consistently when they are presented closer together in space (Spence, Baddeley, Zampini, James, & Shore, 2003; Zampini et al., 2005). This principle has also been demonstrated through neurophysiological measures. Multisensory neurons in the superior colliculus that integrate sensory inputs increase their firing rate multiplicitively when cross-modal sensory cues are presented in close spatial proximity, but decrease when sensory cues are spatially disparate (Stein & Meredith, 1993; Kadunce, Vaughan, Wallace, Benedek, & Stein, 1997).

While linking usually happens when stimuli occur closely together in space, sometimes non-spatially proximate stimulus linking can occur. Perceptual illusions such as the ventriloquist effect demonstrate that multisensory stimuli do not need to originate at exactly the same space and time in order to be integrated (Bertelson & Radeau, 1981; Bertelson, Vroomen, Weigeraad, & de Gelder, 1994; Teder-Salejarvi et al., 2005). In the case of the ventriloquist effect, the presentation of spatially disparate but synchronous auditory and visual stimuli leads to a perceptual shift in the spatial location of the auditory stimulus towards the visual stimulus, along with a lateral shift in the distribution of perception-related ERP activity contralateral to the visual stimulus, activity that has been modeled as arising from the auditory cortex (Bonath et al., 2007).

These behavioral and neural enhancements demonstrate that, at least in some cases, spatially disparate stimuli can be perceptually integrated into a single object.

For multisensory integration in general, however, the farther apart cross-modal stimuli are spatially and temporally, the less likely their physiological multisensory interaction and the less likely it is that they will be perceived as occurring simultaneously and from the same event or object.

Unimodal and Cross-modal Spreading of Attention In theories of object-based attention and perception, it is proposed that environmental stimuli are aggregated into

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elements, which are grouped into various perceptual organizations, which then have the potential to be selectively attended to as “objects” (Scholl, 2001). Early behavioral studies demonstrating a “same-object advantage” have shown that there is increased task performance in reporting two components of a single object versus two components from separate objects (Duncan, 1980). Other studies focusing on visual attention have demonstrated that unattended stimulus components of an attended object receive enhanced processing relative to stimulus components outside of the attended object. In a seminal behavioral study, Egly, Driver and Rafal (1994) compared responses between neurologically normal and parietally-lesioned participants to a cued target detection task. Participants were presented with two outlined rectangles and instructed to detect luminance changes at one of the four ends of the rectangles, which were accompanied by cues that were valid 75% of the time . Participants were faster at detecting targets that appeared on the uncued end of a cued bar compared to the equidistance end of an uncued bar, lending support for object-based attention and a “same-object advantage” (Egly et al., 1994). Using a similar task but also implementing recording of ERPs and functional magnetic brain imaging (fMRI), Martinez et al. (2006) demonstrated that an unattended stimulus within the same object as an attended stimulus elicited enhanced visual cortex activity that resembled a slightly attenuated version of the activity elicited by the attended stimulus.

In another fMRI study of object-based attentional selection, participants were presented with an image of a face transparently superimposed on an image of a house. Participants were instructed to attend to either the image of the face, the image of the house, or to the motion of either image. Though all three attributes were in the same spatial location, attending to the property of one object, such as the face, enhanced the neural representation not only of that property, but also other properties of the object, such as the motion of the face, relative to the corresponding properties of the unattended object (O’Craven, Downing & Kanwisher, 1999). This enhanced processing has also been demonstrated using EEG as well (Schoenfeld et al., 2003), adding the temporal characteristics of this spreading of attention. This finding has been interpreted as a spreading of attention effect within one modality— when one component of an object is attended to, the other components of the same object automatically receive enhanced processing (Egly et al., 1994; Martinez et al., 2006; O’Craven, Downing & Kanwisher, 1999). This enhanced processing has been demonstrated using EEG as well (Schoenfeld et al., 2003), adding some information on the temporal characteristics of this spreading of attention.

In addition to the unimodal spread of attention, a crossmodal spread of attention effect has also been demonstrated. In a recent study on attention and audiovisual integration (Busse, Roberts, Crist, Weissman, & Woldorff, 2005), participants were instructed to covertly direct their attention to one of two lateralized visual streams, selectively at-

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tending to either the left or right as specified, with the task of responding to a target visual stimulus in the designated stream. Half of the visual stimuli were accompanied by a simultaneous, centrally presented, task-irrelevant tone.

Significant enhancement of the neurophysiological activity elicited by the unattended central auditory stimulus was observed when it was presented simultaneously with an attended versus an unattended lateral visual stimulus.

These included a late-onset (>200 ms), negative-polarity ERP wave, as well as increased auditory cortex fMRI activity, indicating enhanced processing of the spatially distinct and unattended but simultaneously presented auditory stimulus (Busse et al., 2005). These findings demonstrated that attention to the visual stimulus could spread to the simultaneous, but unattended and spatially separate, auditory stimulus. This enhanced processing has been replicated both behaviorally and neurophysiologically and is interpreted as a cross-modal, object-based linking process of multisensory stimuli (Donohue et al., in press).

A recent related study examining the temporal and spatial constraints of cross-modal spreading of attention manipulated attention towards spatially disparate visual and auditory events that were within and outside of the temporal window of integration (<150 ms) (Donohue, Roberts, Grent-â&#x20AC;&#x2DC;t-Jong & Woldorff, in press). As with Busse et al. (2005), participants selectively attended to lateralized visual stimulus streams accompanied by unattended,

Articles centrally presented auditory tones, and responded to visual targets. The conditions included presentation of the visual stimulus alone and presentation of the visual and auditory stimuli simultaneously, while also including two additional conditions with a stimulus onset asynchrony (SOA) of 100 ms and 300 ms, with the auditory stimulus delayed after the visual stimulus in both cases. As previously demonstrated in the Busse et al. study (2005), an enhanced negative ERP distribution at frontal-central sites was elicited by the simultaneous but spatially disparate presentation of an attended visual stimulus and an unattended auditory tone, reflecting a cross-modal spread of attention effect that was maximal for the simultaneous condition. Significantly, this same enhanced, negative ERP distribution, although slightly smaller, was also observed in the condition where the unattended tone was delayed after onset of the visual stimulus by 100 ms. In contrast, when the tone was delayed by 300 ms, this spreading-of-attention effect was almost eliminated, presumably due to the greatly decreased temporal proximity between the auditory and visual stimulus components. Thus, cross-modal spread of attention occurs for spatially disparate stimuli that are presented within the temporal window of integration.

On the other hand, spatial linking in the Donohue et al. (in press) study only occurred when the stimuli occurred simultaneously, as reflected by a lateralized shift in auditory ERP activity contralateral to the attended visual stim-

Figure 1: Task Participants were instructed to fixate on a central point while covertly and selectively attending to lateralized visual stimulus streams. The visual stimuli were presented randomly to the lower left or lower right quadrants of the screen for 33 ms (inter-trial interval jittered between 950-1050 ms). Auditory stimuli consisted of a 33 ms, centrally-presented tone pip. Stimulus trials included a Visual Only condition (VO), a Simultaneous condition (Sim), a Delay-100 ms condition, and a Delay-300 ms condition with the tone occurring 100 ms and 300 ms respectively prior to the visual stimulus onset for the latter two conditions.

Subjects responded to a target visual stimulus (two-dot checkerboard image) that appeared in the visual stream on approximately 14% of trials.

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Articles ulus, an effect that was not seen for either of the delayed auditory tone conditions. This pattern of results thus demonstrates a clear dissociation between temporal and spatial linking processes of multisensory stimuli. Additionally, both temporal and spatial linking effects were only observed when the visual stimulus was attended, highlighting the imperative role of attention in multisensory linking processes. Contrary to conclusions of previous behavioral studies that suggested that multisensory integration and the ventriloquist effect are strongly automatic, pre-attentive processes (Bertelson, Vroomen, de Gelder, & Driver, 2000), the neurophysiological evidence suggests that these effects do depend on and interact with attention.

It has not yet been examined whether a cross-modal spread of attention will occur if a near-synchronous but unattended auditory stimulus is presented prior to an attended visual one. While it was expected that neural enhancements elicited by conditions in which stimuli were simultaneously presented would replicate previous findings of cross-modal spread of attention, it is not known whether perceptual integration and processing enhancement for an unattended stimulus would still occur if the unattended stimulus occurred earlier in time than an attended stimulus. It is also unclear whether similar temporal constraints of integration, the currently acknowledged <150 ms window, would still apply in this circumstance.

Accordingly, the present study investigated the temporal and spatial constraints of multisensory integration by comparing activity for synchronously and asynchronously presented auditory and visual stimuli, where the unattended auditory stimulus is presented prior to the visual stimulus, both within and outside of the classic temporal window of integration. It was expected that, despite the unattended auditory stimulus occurring earlier in time than the attended visual stimulus, attention would still spread across modality and space to enhance auditory processing as long as both stimuli occurred within the temporal window of integration (<150 ms). Specifically, it was thought that this spread of attention would be reflected by a negative enhancement of ERP distribution over frontalcentral sites, as previously observed (Busse et al., 2005; Donohue et al., in press), onsetting after presentation of the attended visual stimulus synchronously and near-synchronously with an auditory tone.

Methods and Materials Participants Fifteen adult volunteers (9 female, 14 right-handed) participated in the study. Two additional participants were excluded due to excess physiological artifacts in their EEG data. Informed consent was obtained prior to experimentation, and participants were financially compensated for their time. All procedures conducted were approved by the Duke University Health System Institutional Review Board.

EEG Session Stimuli and Task

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In order to examine possible cross-modal spreadingof-attention under circumstances where visual stimuli are preceded by auditory stimuli, a bilateral attention streaming paradigm similar to that in Donohue et al. (in press) ( Figure 1) was used. Participants were presented with a series of visual stimuli that consisted of checkerboard images containing either 0, 1, or 2 dots. The visual stimuli, each 33 ms in duration, were presented randomly to the lower left or to the lower right quadrant of the screen (at 12.3째 visual angle to the left and right of center, and 3.4째 below central fixation). The inter-trial interval was jittered between 950 and 1050 ms. All auditory stimuli consisted of a centrally presented tone pip that also lasted 33 ms (1200 Hz, 60 dBSL, 5 ms rise and fall periods). Stimulus trials type included a visual stimulus only condition (Visual Only), along with the following multisensory conditions: Simultaneous Visual and Auditory Stimuli (Simultaneous), Visual stimulus delayed by 100 ms (Delay-100 ms), and Visual stimulus delayed by 300 ms (Delay- 300 ms).

All stimuli were presented in Matlab (Mathworks) using Psychophysics Toolbox 3 (Brainard, 1997; Pelli, 1997).

At the beginning of each block during the EEG session, participants were instructed to attend covertly to either the left side (Attend Left) or the right side (Attend Right) of a central fixation point. Participants were instructed to detect and press a button in response to the appearance of an occasional target visual stimulus (a checkerboard image with two dots) when it appeared on the side of the selectively attended visual stream, while also being instructed to ignore all auditory stimuli as they would were task-irrelevant and would not help them with the task. Experimental blocks were approximately two minutes in duration each.

Participants first completed one practice block, and then went on to complete 15 experimental blocks of attending to the left and 15 experimental blocks of attending to the right, with the order of the blocks randomized for all participants. Within each block there were 128 trials, with all trials presented in randomized and counterbalanced order.

Detection accuracy, false alarms, and reaction times (RTs) were recorded. The difficulty level was titrated for each different participant through the adjustment of contrast and dot size within target images so that participants achieved approximately 80% accuracy in detecting the target visual stimulus.

Post-EEG Behavioral Assessment of Simultaneity and Asynchrony Following the EEG recording session, participants were tested behaviorally using a simultaneity judgment task in order to assess their ability to determine the temporal separation between auditory and visual events. Participants were again instructed to attend covertly to either the left or the right side of a central fixation point. Lateralized visual streams were presented as during the EEG session, and auditory information was presented with visual stimuli simultaneously (Simultaneous), 100 ms preceding the visual stimuli (Visual Delay- 100 ms), or 300 ms preceding the Vol 1 Issue 1 | Fall 2011 | neurogenesisjournal.com | 31

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visual stimuli (Visual Delay- 300 ms). In these separate behavioral-only runs, there were no Visual-Only trials.

The inter-trial stimulus interval was jittered from 1450 to 1550 ms in order to allow enough time for participants to make a judgment and respond. Participants were instructed to indicate whether the visual and auditory stimuli were simultaneous with a button press. Participants completed 48 trials for each of the three multisensory trial conditions (i.e., simultaneous, visual delay100, and visual delay 300.

Behavioral Data Analysis Behavioral data obtained during the EEG recording session included reaction time (RT), hits, and false alarms.

Trials with reaction times more than two standard deviations from each subject’s mean reaction time for each condition were excluded from the analysis as outlier trials. The effect of multisensory-SOA conditions on RTs and accuracy were examined using repeated-measures analyses of variance (ANOVAs) comparing factors of stimulus laterality and condition. Any significant effects were followed up with t-tests (alpha level= 0.05).

‘Percent Simultaneous’ Judgment responses were calculated for behavioral data obtained during the simultaneity judgment task, and a repeated-measures ANOVA was conducted to see if these judgments differed between SOA conditions.

EEG Recording and Analysis The electroencephalogram (EEG) was recorded online continuously through a Synamps Neuroscan system (Charlotte, NC) from 64 channels mounted in a customized elastic electrode cap (Electro-Cap International,

Articles Eaton, OH) using a bandpass filter of 0.01-100 Hz at a sampling rate of 500 Hz, and with all data referenced to the right mastoid electrode site. All channel impedances were kept below 5 kΩ. Fixation was monitored with electrooculogram (EOG) recordings using two electrodes lateral to each eye that were referenced to each other, and two electrodes inferior to each eye that were referenced to electrodes on the scalp above the eyes. Recordings took place in an electrically shielded and sound-attenuated experimental chamber.

All offline data processing was done using the ERPSS software package (UCSD, San Diego, CA). Data were filtered offline with a low-pass filter that attenuated signal frequencies above 60 Hz. Artifact rejection was performed to exclude trials that contained eye movements, blinks, excess muscle activity, and excess slow drift. The data were re-referenced to the algebraic average of the left and right mastoid electrodes. Only non-target trials were considered in the analyses in order to focus on the influence of spatial attention and avoid the overlapping effects of large, longlatency ERP waves associated with target detection. Difference waves were calculated based on time-locked ERP averages obtained for each different condition. Repeatedmeasures ANOVAs were conducted on mean amplitude measures of brain activity across subjects using a pre-stimulus baseline of 200 ms in order to compare differences between conditions, and values reported are GreenhouseGeisser corrected.

Extraction of Spreading-of-Attention Activity The data was analyzed to extract the activity associated

Figure 2: Visual attention effects Topographic distributions of the attention effects, comparing attended vs. unattended visual stimuli, showed a significant increased positivity at contralateral occipital sites (P1) between approximately 80-120 ms post-stimulus, followed by a significant increased negativity over contralateral parietal-occipital sites (posterior N1) between 200-240 ms. These effects of visual attention on the ERP distributions indicate that the attentional manipulation was successful, with the P1 and N1 effects apparent contralateral to the side of the attended visual stimulus.

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Articles with processing of the task-irrelevant auditory tone as a function of whether it was accompanied by an attended or unattended visual stimulus. ERPs for each condition were time-locked to the onset of the visual stimulus and all auditory stimuli were presented centrally. In order to isolate ERP activity associated with the auditory stimulus in the three multisensory conditions, ERP from the Visual Only condition was subtracted from that of the Simultaneous, Delay-100 ms and Delay-300 ms conditions. This separated the contribution of the visual stimuli and extracted the activity linked to the processing of the auditory stimulus under each multisensory attentional context.

The spreading of attention activity was extracted and analyzed for all three multisensory conditions. The extracted auditory responses to the tones accompanied by an attended versus an unattended lateral visual event were then compared in order to examine the spread of attention across modality and space to the centrally-presented tones.

Conditions were also collapsed across the left and right sides to obtain the attentional spreading effect independent of visual stimulus lateralization.

Results Behavioral results for visual attention task during EEG runs Response times (RTs) and detection accuracy for the target visual stimuli were recorded for the visual attention task during the EEG session. There were no significant differences in accuracy for visual target detection between any of the audiovisual SOA conditions, with each condition close to the predetermined titration level of 80% accuracy (F<1, Visual Only, Simultaneous, Delay 100 ms and Delay 300 ms) (Supplemental Fig. 1A). There were significant differences between the RTs between these conditions, however, as reflected by significant main effect of condition in the analysis of variance (ANOVA) (F(2.13, 34.08)= 5.68, p<0.05). Specific contrasts revealed that the Visual Only condition RTs were significantly slower than the Delay-100 ms condition RTs (t(15)=3.70, p<0.05, VO M= 0.58 s, VO SD= 0.06 s, D100 M= 0.57 s, D100 SD= 0.05 s) and the Delay-300 ms condition RTs (t(15)=2.20, p<0.05, D300 M= 0.57 s, D300 SD= 0.06 s).

Also, the Simultaneous condition RTs were significantly slower than the Delay-100 ms condition RTs (t(15)= 3.58, p<0.05, Sim M= 0.58 s, Sim SD= 0.06 s). In summary, RTs in the Visual Only condition were slower than those in both the delay SOA conditions, while RTs in the Simultaneous condition were slightly slower than those in the Delay-100 ms condition. An additional 2x2 (Condition by laterality) ANOVA was conducted to determine if the laterality of the stimuli had any influence on RTs. It revealed a small effect of stimulus laterality, with significantly slower RTs in responses to right visual stimuli (F(1, 16)= 17.65, p<0.05) than to left ones (Right mean RT= 580 ms, Left mean RT= 570 ms).

Behavioral results for simultaneity judgment task Data recorded for the behavioral simultaneity judg-

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ment task included the percentage of targets judged as simultaneous (Supplemental Fig. 2). An ANOVA comparing stimulus laterality and the three SOA conditions (Sim, D100 and D300) revealed a main effect of condition (F(1.15, 14.89)= 11.19, p<0.05). Post-hoc, two-tailed ttests showed that participants judged significantly more targets as simultaneous in the Simultaneous condition (0.85.87%) than in the Delay-300 ms condition (49.95%) (t(9)=4.10, p<0.05, Sim M= 85.57%, Sim SD= 0.12, D300 M= 49.95%, D300 SD= 0.26). They also judged significantly more targets as simultaneous in the Delay-100 ms condition than in the Delay-300 condition (t(9)=4.15, p<0.05, D100 M= 85.54%, D100 SD= 0.13).

Effects of visual attention on visual stimuli ERP distributions To verify that the manipulation of participantsâ&#x20AC;&#x2122; covert visual spatial attention was effective, visual spatial attention effects to the non-target visual stimuli during Visual Only trials were examined. Characteristic visual attention modulations of the early sensory ERP components contralateral to the direction of visual attention were observed for both Attend Left and Attend Right conditions (Hillyard and Anllo-Vento, 1998). Comparing attended versus unattended visual stimuli showed an increased positivity at contralateral occipital sites (P1 effect) between approximately 80-120 ms post-stimulus. The P1 effect was followed by an increased negativity over contralateral parietal-occipital sites (posterior N1 effect) between 200240 ms (Fig. 2). An ANOVA including the factors of attention, stimulus laterality (left vs. right visual field), and hemisphere (left vs. right electrode location) confirmed the presence of a significant contralateral P1 attention effect over the latency window 80-120 ms, as reflected by a significant three-way interaction across the occipital sites To1/To2, O1i/O2i, and P3i/P41 (F(1, 14)=12.84, p<0.005). The analyses also showed a significant N1 attention effect from 200-240 ms at posterior sites P31/P41, P3a/P4a, and O1/O2 (F(1, 14)=7.28, p<0.01). These effects of visual attention on the ERP distributions confirm that participants were indeed directing their attention towards the instructed lateralized visual stimulus stream.

Cross-Modal spread of attention as a function of SOA Simultaneous Condition In order to extract ERPs of the central auditory tone elicited by attending to a lateralized visual stimulus, the ERPs of attended visual stimuli occurring alone were subtracted from the ERPs of attended visual stimuli occurring simultaneously with a task-irrelevant centrally-presented tone (Fig. 3). Similarly, to extract the ERPs to the central tone when it occurred with an unattended lateral visual stimulus, the ERPs of unattended visual stimuli occurring alone were subtracted from the ERPs of unattended visual stimuli occurring simultaneously with a task-irrelevant central tone. These subtractions remove visual attention effects and visual components of the multisensory stimuli, resulting in ERP difference waves that reflect extracted auditory activity elicited by the central tones as a funcVol 1 Issue 1 | Fall 2011 | neurogenesisjournal.com | 33

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tion of their multisensory attentional context (Busse et al., 2005; Donohue et al., in press).

The extracted auditory activity of the simultaneous condition elicited by the simultaneous presentation of a central tone with an attended versus unattended lateral visual stimulus appeared as an enhanced, negativity from approximately 200-900 ms at frontal-central sites Fz, FCz, FC1, and FC2 (F(1,14)= 13.57, p<0.005) (Supplemental Fig. 3).

The ERPs at times before and after the period of 200-900 ms did not differ significantly. These results replicated the multisensory spread of attention from vision to audition ERP effects that have been reported in previous studies (Busse et al., 2005; Donohue et al., in press).

Delay-100 ms Condition Auditory activity during the Delay-100 ms condition

Articles was extracted using the same steps as those detailed for the Simultaneous condition. The frontal central sites tested in the Simultaneous condition were tested again, and a similar frontal-central, enhanced negativity was observed in the Delay-100 ms condition with a significant conditionbased difference between attended vs. unattended stimuli from 200-900 ms (F(1, 14)= 9.67, p<0.01) (Supplemental Fig. 3). As in the simultaneous condition, there was no enhanced auditory activity indicating the spread of attention effect until 200 ms after visual stimulus onset (which in this case was 300 ms after the auditory stimulus component).

Delay-300 ms Condition Auditory activity during the Delay-300 ms condition was extracted using the same subtraction processes detailed for the Simultaneous and Delay-100 ms conditions

Figure 3: Extractiion of multisensory spread of attention activity Extraction of Multisensory Spread of Attention Activity. The difference wave contrasts show the process for extraction of auditory ERP under different multisensory attentional contexts. All traces are for frontal site Fz. The extracted auditory ERP responses for the attended Simultaneous condition (Sim) were obtained by calculating the ERP difference waves for the attended-visual Sim minus the attended-visual Visual Only condition (VO). The extracted auditory ERP responses for the unattended Sim condition were similarly derived from the unattended-visual Sim and the unattended-VO conditions. The difference waves for the extracted activity to the central auditory stimulus presented with an attended and unattended lateral visual stimulus were compared. The extracted auditory ERP responses for the 100 ms and 300 ms SOA conditions were similarly derived and the difference waves obtained were also compared in the same manner.

The difference waves between the extracted auditory responses for each condition when they occurred in the context of an attended minus unattended lateral visual stimulus were overlaid for each of the SOA conditions. The extracted auditory activity elicited by the presentation of a central tone with an attended versus unattended lateral visual stimulus showed the greatest attentional difference in the Simultaneous condition with diminished difference in the Delay-100 ms condition and minimally significant difference in the Delay-300 ms condition.

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Figure 4: Topographic voltage distributions comparing SOA and laterality This figure shows the topographic distribution plotted for the differences between extracted auditory activity for attended minus unattended visual conditions from 200-250 ms (calculated as in Figure 5), comparing SOA conditions and laterality. Though there is a qualitative difference in lateralization of auditory activity in the Left visual stimulus Simultaneous condition, an ANOVA that included the factors of attention, stimulus laterality, and hemisphere however indicated no significant effect of attention in any of the conditions.

(Fig. 3 and Supplemental Fig. 3). Analyses of the frontalcentral sites (Fz, FCz, FC1, and FC2) revealed that the observed frontal-central negativity was only a marginally significant effect onset from 200-900 ms (F(1, 14)= 4.52, p<0.05). An effect that was unique to the Delay-300 ms condition included an enhanced left-lateralized negativity onset from 100 ms to 250 ms, with the most apparent distribution shift occurring in the 200-250 ms time period (Supplemental Fig. 3). The activity prior to 200 ms was non-significant (F<1). Because this shift in distribution was thought to possibly reflect anticipatory motor activity, a target analysis was performed for the 200-250 ms time window for all three conditions. Instead, beginning around the 200-250 ms window, a bilateral negativity was observed in all three conditions that became more leftlateralized after 250 ms until the time of the P300 effect, which is not elicited in general until after stimuli have been cognitively evaluated (Pritchard, 1981). The pre-200 ms activity in the Delay-300 ms condition thus does not seem to be related to anticipatory motor activity. Additionally, any potential effect related to the multisensory spread of attention was greatly attenuated.

Spatial shifts The spreading of attention activity in each multisensory condition was analyzed in order to examine whether spatial shifts occurred in auditory stimulus localization associated with the ventriloquist effect (where the spatial location of an auditory stimulus is perceptually shifted towards that of a simultaneous but spatially disparate visual stimulus) (Bertelson & Radeau, 1981; Bonath et al., 2007) (Fig. 4). Perceptual shifts in the location of the centrally presented tone towards the location of the lateral visual stimulus would result in a shift of the auditory ERP distribution contralateral to the attended visual stimulus (Bonath et al. 2007; Donohue et al., in press). For each condition, the extracted auditory activity of the unattended left visual stimulus was subtracted from the extracted auditory activity of the attended left visual stimulus, and the same was done for attended and unattended right visual stimulus associated auditory activity, after subtracting

the Visual Only trials. The time period analyzed was 200250 ms for all three conditions. This subtraction process was done in order to reveal whether the initial neural activity related to attentional spread was shifted towards the hemisphere contralateral to the attended visual stimulus, as previously reported for the simultaneous condition in Donohue et al. (in press). Qualitative differences in lateralization of auditory activity were again observed only in the Simultaneous condition, where the attentional spread ERP distribution was shifted contralateral to the side of the attended visual stimulus. This shift was also clearer for activity in the Simultaneous left visual stimulus condition than in the Simultaneous right visual stimulus condition.

However, an ANOVA that included the factors of attention, stimulus laterality, and hemisphere showed that there was no significant lateralization effect of attention in any of the conditions, suggesting that in most cases the stimuli were not being consistently linked spatially (F<1).

Discussion In addition to reinforcing current understanding of the temporal and spatial principles underlying multisensory integration and the spread of attention across components of a multisensory object, this study further elucidated the temporal constraints of cross-modal spread of attention, including being the first to demonstrate that attention can spread across modality and space to an unattended stimulus that precedes an attended stimulus. Both behavioral and neurophysiological measures reflected that the processing of stimuli in this experimental context occurred within the classic temporal window of integration. Although no significant spatial linking of stimuli was found even for the simultaneous conditions here, there was a trend for such an effect here, and it was speculated that the lack of replication for this effect may be due to there being less statistical power in the present study. Notably, both effects related to cross-modal spread of attention and preliminary evidence of spatial linking only occurred in the context of attention.

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taneous when they were actually presented simultaneously and when the auditory stimulus was presented 100 ms before the visual stimulusâ&#x20AC;&#x201D; i.e., both within the temporal window of integration (<150 ms) -- but not when the auditory stimulus was presented 300 ms before the visual stimulusâ&#x20AC;&#x201D; i.e. outside of the temporal window of integration (Meredith, Nemitz & Stein, 1987). Furthermore, neurophysiological measures indicating the spread of attention to auditory stimuli were observed when the visual and auditory stimuli occurred simultaneously or with an SOA within the temporal window of integration, but not when the visual stimulus was delayed by 300 ms. Thus, temporal linking of stimuli within the currently acknowledged window of integration (<150 ms) seems to be a prerequisite for the cross-modal spread of attention, or visaversa (Meredith, Nemitz & Stein, 1987; Stone et al., 2001; Zampini, Shore, & Spence, 2003; Zampini et al., 2005; Schneider & Bavalier, 2003; Donohue et al., in press).

The spatial linking of disparate, attended visual stimuli and unattended auditory stimuli has been demonstrated by a shift in ERP distribution when stimuli are simultaneously presented, but not when stimuli are asynchronous but within the temporal window of integration (Donohue et al., in press). In the present study, although neural activity reflecting the ventriloquist effect was expected when the spatially disparate visual and auditory stimuli were presented simultaneously, there was no significant spatial linking effect observed here (Bonath et al., 2005; Donohue et al., in press). Although there was thus no demonstrated dissociation of temporal and spatial linking, it is possible that this is due to limitations such as lower power than was obtained in the previous study (Donohue et al., in press).

Notably, all observed temporal and spatial linking as well as cross-modal spread of attention that occurred resulted from the attentional manipulation, as no significant SOA interaction effects were found in the unattended conditions.

Temporal linking As reflected by behavioral measures of perceptual simultaneity and ERP measures of cross-modal spread of attention from vision to audition, this study found that temporal linking of multisensory stimuli occurs only within the temporal window of integration. The findings further emphasize the importance of attention and the temporal window of integration for cross-modal spreading of attention previously demonstrated in other studies (Donohue et al., in press). Other studies, both behavioral and neural, have also demonstrated the inverse relationship observed between SOA and the likelihood of perceptual integration of multisensory information (Schneider & Bavalier, 2003; Zampini et al., 2005; Busse et al., 2005; Donohue et al., in press). A novel finding of the present study is that attention can spread from vision to audition across space within the window of temporal integration even when the unattended auditory stimulus precedes the attended stimulus. In addition to evidence from partici36 | neurogenesisjournal.com | Fall 2011 | Vol 1 Issue 1

Articles pantsâ&#x20AC;&#x2122; behavioral perceptions of near-synchronous stimuli as occurring simultaneously, because neural activity related to enhanced auditory processing did not occur until after visual stimulus onset, it was demonstrated that the auditory and visual stimuli were truly temporally linked.

Although it may be expected that attention cannot spread to events that occur earlier in time than an attended event, it would appear that via this temporal linkage attention can indeed spread from one to the other cross-modally as though they were components of a single perceptual object. Moreover, in comparison to the previous Donohue et al. study, it would appear that the actual order of the stimulus components does not affect their multisensory integration, provided they were within the window of integration. The constraints of a temporal window of integration are known to apply similarly to other multisensory phenomena as well, including learned relations between semantic multisensory information, semantically unrelated stimuli, and audiovisual information involved in speech processing (Van Atteveldt, Fromisano, Blomert, & Goebel, 2007; Meredith et al., 1987; McGrath & Summerfield, 1985).

For the condition in which the audiovisual SOA was outside of the window of integration, in particular where the auditory stimulus preceded the attended visual stimulus by 300 ms, there was a minimally significant left-lateralized negative enhancement, although this effect did not seem to reflect a cross-modal spread of attention. Interestingly, the behavioral data collected during the EEG session showed a significant effect due to stimulus laterality as participants were faster on average in responding to visual stimuli presented on the left. Since any neural representation for this behavior would be represented lateralized towards the right hemisphere and not enhanced in the left hemisphere, the distribution observed in the Delay-300 ms condition would not seem to be explained by this behavior.

Left lateralization of the ERP distribution in the Delay-300 ms condition was considered and it may have perhaps reflected anticipatory motor activity. Because all participants responded to targets using their right hand, any potential motor-related activity that was consistent throughout the subject pool could be expected to appear consistently contralateral to the hand used, and thus should have subtracted out. In studies of motor priming, shorter RTs are elicited when a movement is validly primed compared with when a movement is invalidly or ambiguously primed (Rosenbaum & Kornblum, 1982).

Notably, the RTs in the SOA conditions during the EEG session were significantly faster than in the simultaneous and visual alone conditions (Supplemental Fig. 1B). Thus, in the present study, it is possible that there was a priming effect associated with the unattended auditory stimulus, as it preceded the attended visual stimulus by 100 ms and 300 ms. As reflected by imaging studies and other neurophysiological measures such as ERPs, the priming- associated advantage in RT is thought to be partially due to

Articles preparatory processing in cortical motor areas (Leuthold & Jentzsch, 2002; Dassonville et al., 1998; Lee, Chang & Roth, 1999). Additionally, lateralized ERP components typically associated with shifts in spatial attention that have also been demonstrated to be elicited by visual cues that prime for a particular motor response suggest that there is a close link between attention and motor response preparation processes, although some studies have found that priming for response preparation triggers activity in closely-linked but separate attention-related and premotor areas (Eimer, Forster, Van Velzen, & Prabhu, 2005; Van der Lubbe et al., 2000; Mathews, Dean & Sterr, 2006). The target analysis performed to look at potential motor priming activity revealed similar patterns across all conditions, and thus it was determined that the lateralized enhancement observed in the Delay-300 ms condition was not due to preparatory motor activity. Instead, it may be necessary to increase statistical power in order to successfully examine the neural activity for conditions where an unattended auditory stimulus precedes an attended visual stimulus by a greater SOA than the temporal window of integration.

Another interesting effect observed was a 200 ms delay in onset of the spreading-of-attention auditory activity in both the simultaneous and Delay-100 ms conditions. This was similar to the effect observed in the previous study

by Donohue et al. (in review), where significant auditory activity did not occur until 200 ms after onset of the attended visual stimulus in the simultaneous condition, and 300 ms after onset of the attended visual stimulus when the onset of the auditory tone was delayed by 100 ms (the 100 ms delay in onset of significant auditory activity reflected the 100 ms delayed onset of the auditory stimulus).

In our study, the auditory tone was either simultaneous with the visual stimulus or preceded the visual stimulus, and so in both the simultaneous and Delay-100 ms condition the delay in activity after the attended visual stimulus was 200 ms. Taken together, these findings suggest the need for some preliminary visual stimulus processing of the attended visual stimulus prior to the occurrence of cross-modal spread of attention.

Spatial linking The presentation of an unattended, central auditory tone simultaneously with an attended, lateralized visual stimulus elicited a shift in ERP distribution contralateral to the side of the attended visual stimulus that was most clearly observable in the Simultaneous left visual stimulus condition. Although this effect did not reach significance, thus not supported the spatial linking during simultaneous occurrence, a cross-modal spread of attention associated with the ventriloquist effect has previously been demonstrated with a similar task set-up including simultaneous, spatially disparate stimuli (Donohue et al., in press). Furthermore, the distribution and timing of the contralateral shift in ERP resembled the activity elicited in an explicit auditory localization task, which notably also showed shifts in behavioral perception of the auditory stimulus

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towards the visual stimulus (Bonath et al., 2007). In our study, without an explicit localization task it was not possible to determine what percentage of auditory and visual stimuli were actually co-localized. However, it is thought that an increase in statistical power would at least allow for a more clear analysis of the observed spatial shift effect and likely lead to replication of previous findings.

It is less clear as to why the contralateral shift in ERP was more apparent for the left visual stimulus condition than for the right visual stimulus condition. Additionally, although non-significant, there was also a slight lateralization of activity in the Delay-100 ms and Delay-300 ms right visual stimulus condition contralateral to the stimulus. It is possible that the orientation of the participants was biased behaviorally towards a particular visual stimulus stream. Although the behavioral data showed a significant effect of stimulus laterality, with faster responses to left visual stimuli, this performance is not likely to be related to the effects observed. Faster RT suggests enhanced processing of visual stimuli that would lead to enhancements contralateral and not ipsilateral to the attended location as seen (Hillyard & Anllo-Ventro 1998; Brefczynski & DeYoe 1999; Posner & Petersen 1990; Stein & Stanford 2008) (Fig. 4).

The slight lateralization elicited in the condition with an SOA of 100 ms may suggest that spatial linking can occur even when an unattended auditory stimulus precedes the attended visual stimulus. Additionally, the decreased shift in lateralization of the auditory stimulus towards the visual stimulus with increasing temporal separation is consistent with behavioral studies of temporal asynchrony in the ventriloquist effect (Lewald & Guski, 2003). If it can be demonstrated that there is a significant shift of auditory activity contralateral to a visual stimulus, it would indicate that attention may spread cross-modally to an unattended component of a perceptual object regardless of whether it occurs before or after an attended component as long as it is within the temporal window of integration. The modulation of this effect by attention and the importance of the temporal constraints suggest that the ventriloquist-like effect is not pre-attentively processed.

Attentional modulation of multisensory integration and crossmodal spread Both the significant neural activity indicating the cross-modal spread of attention within the temporal window of integration and the slight lateralization of auditory activity contralateral to the visual stimulus associated with spatial linking occurred in the context of attention.

The results are thus consistent with findings form previous studies of both humans and animals that have demonstrated the necessity of attention for the early integration of multisensory stimuli and the modulation of multisensory integration processes (Talsma & Woldorff, 2005; Talsma, Doty & Woldorff, 2007; Lakatos et al., 2009; Busse et al., 2005; Donohue et al., in press; reviewed in Talsma et al., 2010).

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Conclusions In summary, the findings demonstrate that visual attention can spread cross-modally to a spatially disparate, task-irrelevant auditory stimulus as long as both stimuli occur within the temporal window of integration (<150 ms), even in the case where the irrelevant auditory stimulus occurs earlier in time than the attended visual stimulus. There is maximal integration and spread of attention when the stimuli are presented simultaneously, and increasingly diminished effect with increasing SOAs. Additionally, when spread of attention occurs, i.e., when the stimuli are simultaneous and when the visual stimulus is preceded 100 ms by the unattended auditory stimulus, it happens approximately 200 ms after onset of the attended visual stimulus, suggesting the need for some initial processing of the attended visual stimulus component before attention can spread cross-modally. The findings did not indicate any significant spatial linking across modality and space, although that additional statistical power seems likely to make the slightly observed lateralization of auditory activity more apparent. Overall, it appears that attention is necessary under these circumstances in order for multisensory integration to occur, with cross-modal enhancements of the auditory activity occurring only in the context of an attended visual stimulus. The apparent lateral shifts of the auditory stimulus contralateral to the visual stimulus were also observed only when the visual stimulus was attended. The findings of this study contribute to current understanding of the temporal and spatial constraints of multisensory integration, and the way these processes are influenced by attention.

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Stein BE, Stanford TR. (2008). Multisensory integration: current issues from the perspective of the single neuron. Nature Reviews Neuroscience, 9:255-266.

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The effect of temporal asynchrony on the multisensory integration of letters and speech sounds. Cerebral Cortex, 17(4): 962-974.

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Wallace MT, Roberson GE, Hairston WD, Stein BE, Vaughan JW, Schirillo JA. (2004). Unifying multisensory signals across time and space. Experimental Brain Research, 2:252-258.

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Edna Andrews, PhD eda@duke.edu

This lab is involved in two major projects: (1) fMRI studies on multilingualism, and (2) speech perception studies, specifically studies of the perception of spoken and sung phonemes across languages. The fMRI multilingualism project is on-going and includes both discrete and longitudinal studies. Students who work in this lab will be trained in computer technologies appropriate to fMRI research. Students who work on this project are not required to know the language of the study.

Roberto Cabeza, PhD cabeza@duke.edu

This lab investigates the neural mechanisms of memory in young and older adults using functional neuroimaging techniques, such as fMRI. Research topics include emotional memory, false memory, and memory-attention interactions.

Christine Drea, PhD cdrea@duke.edu

The Drea lab studies mammalian social and reproductive behavior in primates.

Through a combined laboratory and field approach, they investigate reproductive and socio-endocrinology, genital and developmental morphology, and social behavior. They study how males and females differentiate to meet their respective sex roles, how they negotiate social interactions with group members, and how they solve everyday problems in the context of group living.

Cagla Eroglu, PhD c.eroglu@cellbio.duke.edu

The Eroglu lab is interested in understanding how central nervous system (CNS) synapses are formed. They believe astrocytes are an important player in the formation of such synapses. Their lab seeks to answer questions such as what are the secreted signals coming from astrocytes that regulate synapse formation, how do astrocyte-secreted factors lead to synapse formation, and what is the role of astrocyte-induced synapse formation in the development and maintenance of CNS.

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Lasana Harris, PhD bsclab@gmail.com

The Boundaries of Social Cognition lab solves philosophical questions about human behavior by combining social psychology, affective/cognitive neuroscience, and philosophy of the mind. They address questions related to morality, economic decisions involving social and monetary rewards and punishment, and the effect of competition and cooperation on decision-making. Using fMRI, EMG, and GSR, the BSC lab focuses on human perception and decision-making.

Scott Huettel, PhD scott.huettel@duke.edu

Huettel Laboratory uses a combination of behavioral, genetic, physiological, and neuroscience techniques to discover the mechanisms that underlie economic and social decision making. This broad research programâ&#x20AC;&#x201C; which includes collaborations with neuroscientists, psychologists, behavioral economists, and business and medical faculty â&#x20AC;&#x201C; falls within the emerging interdiscipline of neuroeconomics.

Richard Keefe, PhD michael.kraus@duke.edu

Keefe lab studies cognition and perception in schizophrenia and related clinical disorders. They are conducting studies in Singapore of the perceptual and cognitive deficits that may predict psychosis. Here in Durham, they are completing clinical trials on behavioral and pharmacologic treatments for cognitive impairment in schizophrenia, and are working to understand the auditory perceptual abnormalities that may underlie emotion identification difficulties.

Kevin LaBar, PhD klabar@duke.edu

Research in this laboratory focuses on understanding how emotional events modulate cognitive processes. They aim to identify brain regions that encode the emotional properties of sensory stimuli, and to show how these regions interact with neural systems supporting social cognition, executive control, and memory functions. Techniques used are psychophysiological monitoring, fMRI, and behavioral studies in healthy adults as well as psychiatric patients. This approach capitalizes on advances in the field and may lead to insights into cognitiveemotional interactions in the brain.

Hiro Matsunami, PhD matsu004@mc.duke.edu

Matsunami lab is interested in the chemical senses, the sense of smell and taste.

Using molecular genetics, genomic, and cell biology approaches, they study how chemicals such as odors, tastants and pheromones interact with the receptors expressed on the surface of the sensory cells and elicit unique perception and/ or behavior.

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Jim McNamara, MD jmc@neuro.duke.edu

Dr. McNamaraâ&#x20AC;&#x2122;s laboratory seeks to elucidate the mechanisms of epileptogenesis, the process by which a normal brain becomes epileptic. Understanding the mechanisms of epileptogenesis in molecular terms may provide novel targets for pharmacologic interventions aimed at prevention of epilepsy or limiting its progression. They seek to elucidate the signaling pathways activated by TrkB, or the neurotrophin receptor, that promote limbic epileptogenesis. They are also using genetically modified mice to examine the effects of TrkB in additional models of limbic epileptogenesis.

Steve Mitroff, PhD elise.darling@duke.edu

The Mitroff lab explores malleability of visual cognition - how various experiences (e.g. videogame playing) and traits (e.g. tendencies towards ADHD and Autism) affect visual and attentional abilities. Through an array of experimental tasks and survey responses, this lab is geared towards identifying and enhancing superior searching abilities.

Michael Platt, PhD platt@neuro.duke.edu

The Platt Laboratory probes the ways in which information about the current state of the world gathered by the senses is combined with estimates of costs and benefits, uncertainty, social context, and individual-specific variables like internal state, social status, and risk tolerance to guide behavior in monkeys, adult and developing humans, mice, and other animals.

Richard Premont, PhD richard.premont@duke.edu

Premont lab studies how multiple signaling pathways initiated by neurotransmitters and neuromodulators interact and coordinate within target cells to produce integrated physiological responses. They use cell culture systems to address mechanistic questions, and knockout mice to assess global behavioral functions.

As a model system, they focus on the GIT/PIX complex. They are examining mice lacking GIT1 as a model for mental retardation, and mice lacking GIT2 as a model for post-traumatic stress disorder.

Nestor Schmajuk, PhD nestor@duke.edu

Dr. Schmajuk has developed neural network models of classical conditioning, operant conditioning, animal communication, spatial learning, cognitive mapping, and prepulse inhibition. Using these neural networks he has described the effects of hippocampal, cortical, and cerebellar lesions, as well as the results of the administration of dopaminergic and cholinergic drugs, in different sensory, learning and cognitive paradigms.

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Laboratories Debra Silver, PhD debra.silver@duke.edu

Silver lab studies regulation of neural progenitors in the developing brain. They employ genetics, genomics and cell biology techniques to identify genes that influence neural stem cell division, neuron production, and brain size. Defects in these processes are associated with broad classes of neurodevelopmental diseases.

Jim Voyvodic, PhD jim.voyvodic@duke.edu

Research in this lab focuses on using fMRI to study information processing mechanisms in the nervous system. Particularly, Dr. Voyvodic is interested in how the visual system represents 3-D depth when processing visual scenes. The lab’s second main focus is applying fMRI as a clinical tool to aid in the treatment of brain tumors and epilepsy.

Anne West, MD PhD west@neuro.duke.edu

This laboratory seeks to understand at a cellular and molecular level how neuronal activity regulates the formation and maturation of synapses both during brain development and in response to plasticity-inducing stimuli, and ultimately to use genetic model systems to investigate how defects in this process lead to cognitive and behavioral dysfunction.

Leonard White, PhD len.white@duke.edu

White lab’s primary research interest is to understand how sensorimotor experience in early life influences—for better or worse—the formation and maturation of functional neural circuits. Work in his lab uses neuroanatomical techniques to relate structure to function in the developing cerebral cortex and in the brainstem.

Marty Woldorff, PhD woldorff@duke.edu or ken.roberts@duke.edu

The fundamental cognitive function of attention enables us to select and extract from moment to moment the most important information from our complex multisensory world and ongoing neural processes. This lab uses a combination of electrophysiological (EEG, ERP), functional neuroimaging (fMRI), and behavioral measures to study the cognitive neuroscience of attention.

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Lily Pham

Kathryne Wood

Kelly Murphy

Rory Lubner

Editor-in-Chief

Publishing Editor

Managing Editor

Managing Editor

Lily Pham is a senior from Fairfax, Virginia. She is double majoring in Neuroscience and Biology, with a concentration in Pharmacology, and a minor in Chemistry. Lily hopes to pursue an MD/PhD to study neuropharmacology.

Lily teaches a neuroscience seminar at NCSSM and is the president of COSIGN (Collegiate Student Interest Group in Neurology/Neuroscience.)

Kathryne Wood is from Atlanta, Georgia. She is a senior neuroscience major and is currently researching drug addiction in rodent behavioral models. Katy’s interest in science writing was sparked by a 2008 trip to Sweden to report on the World Water Conference. In addition to being the Publishing Editor for Neurogenesis, Katy is also a co-editor-in-chief for Encompass, Duke’s ethics magazine.

Kelly Ryan Murphy is a junior from Glendale, Arizona, pursuing a Neuroscience major and Chemistry minor. She currently serves as President of the Neuroscience Majors’ Union and volunteers at the VA Hospital. As a managing editor and one of the original founders of Neurogenesis, she is very excited to help cultivate a culture of undergraduate neuroscience research at Duke.

Rory Lubner is a junior from Seattle, Washington and is majoring in Neuroscience and minoring in Chemistry. You can often find Rory volunteering for Duke’s Best Buddies Program and the DUMC Emergency Room, as well as dancing at many campus events as a member of Defining Movement (defMo). He hopes to attend medical school after graduating from Duke.

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About Us Â

Christine Lee

Rolando Rengifo

Associate Editor

Associate Editor

Graduated Founder Graduated Founder

Biqi Zhang is a sophomore studying neuroscience and genetics. Biqi works in the Lab of Neurogenetics, researching the effect of stress and genes on amygdalar reactivity. She also spends her time cardio dancing, enjoying Chinese cooking with family, and working at DUMC. In the future, she hopes to combine her love of science and people by becoming a physician and public health worker.

Christine Lee is a sophomore double majoring in Neuroscience and History. She currently works at the Center for Cognitive Neuroscience under Dr. Woldorff on attention and memory research. She serves as co-publicist for the Neuroscience Majorsâ&#x20AC;&#x2122; Union, and hopes to pursue a career in global health. Christine is grateful for the opportunity to help shape the future of Neurogenesis.

Biqi Zhang

Rolando Rengifo is a recent Duke graduate from Mexico City who majored in Chemistry and Neuroscience. Rolando helped reinstate COSIGN in 2008. Rolando was a member of the Delta Kappa Epsilon Fraternity, Club Soccer, and RLHS among other organizations, a founder of Neurogenesis, He is now a graduate student at Emory University seeking a Ph.D. in Chemistry.

Austin Mattox Austin Mattox is a recent Duke graduate from Winston-Salem, North Carolina who majored in Chemistry and Biology. Austin helped reinstate COSIGN, and participated in public and global health projects around the world. He is currently researching at the Institut Pasteur in Paris and aims to pursue an MD/PhD in cancer biology as a way to eliminate health disparities.

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Neurogenesis is a member of Duke Undergraduate Publication Board Š Copyright 2011