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Library and Archives Canada Cataloguing in Publication Amthor, Frank
Neuroscience for dummies / Frank Amthor. Includes index.
Issued also in electronic formats.
ISBN 978-1-118-08686-5
1. Neurosciences--Popular works.
2. Brain--Popular works. I. Title.
QP376.A57 2011 612.8’2 C2011-902699-6
ISBN 978-1-118-08686-5 (paper); 978-1-118-08967-5 (ePDF); 978-1-118-08968-2 (ePub); 978-1-118-08966-8 (Mobi)
Printed in the United States of America
1 2 3 4 5 RRD 16 15 14 13 12
About the Author
Frank Amthor is a professor of psychology at the University of Alabama at Birmingham, where he also holds secondary appointments in the UAB Medical School Department of Neurobiology, the School of Optometry, and the Department of Biomedical Engineering. He has been an NIH supported researcher for over 20 years and has also been supported by the U.S. Office of Naval Research, the Sloan Foundation, and the Eyesight Foundation. His research is focused on retinal and central visual processing and neural prostheses. He has published over 100 refereed journal articles, book chapters and conference abstracts.
Dr. Amthor’s career has been devoted to understanding neural computation, both for its own sake, and for the sake of making neural prosthesis that restore and augment human function. His specific research has been to investigate complex neural computations in retinal ganglion cells, the first locus in the visual system of highly specific and nonlinear analyses such as motion and directional selectivity. The investigative techniques he has used include virtually the entire suite of single cell neurophysiological techniques, including single cell extracellular recording, sharp electrode intracellular recording and staining, patch clamp recording, optical imaging with both calcium and potentiometric dyes, dual electrode recording, and, most recently, microelectrode array recording. His current research interests involve further translating basic research on the retina to the development of neural prostheses both for the visual system and for other disabilities.
No professional neuroscientist is competently up to date on the entire brain or nervous system, and what we know and understand about it is constantly changing. Although a great deal of time and effort has gone into making sure the material in this book is accurate and up to date, any mistakes within are mine alone. If you find an error or would like to make any other comments about this book, feel free to contact me at amthorfr@gmail.com.
Dedication
To Becky, my partner in life, and the mother of my three wonderful children.
To Philip, Rachel and Sarah, for being the world’s best kids and now the world’s hope for the future.
To my parents, Agnes and Ryder, and my stepfather, Jim, who launched me into this world and gave me guidance for living in it.
To all my teachers who thought I was someone worth investing time in.
Author’s Acknowledgments
This book owes its existence first to my agent, Grace Freedson (The Publishing Network). I thank Robert Hickey, acquisitions editor, for working with me to develop the framework for the book, and Wiley’s Graphics Department for their work on the illustrations throughout this book. Really special thanks go to Tracy Barr, the project editor, who improved virtually every sentence in the book. I cannot thank her enough for her kind diligence.
Publisher’s Acknowledgments
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3: Understanding How Neurons
Part III: Moving Right Along: Motor Systems
Intelligence: The Thinking Brain and Consciousness
Brain
Getting
Chapter 15: Learning and Memory
Neuroscience For Dummies
Neuroscience For Dummies
Introduction
The central mystery about the brain is simply this: How can a bunch of interconnected cells make each of us what we are — not only our thoughts, memories, and feelings, but our identity. At present, no one can answer this question. Some philosophers think it is not answerable in principle.
I believe we can understand how the brain makes us what we are. This book, while surely not containing the complete answer, points the way to what the answer looks like: In short, the brain is made of neurons, each of which is a complex little computer. Parts of the nervous system make suggestions to the rest of it about what you should do next. Other parts process the sensory inputs you receive and tell the system how things are going so far. Still other parts, particularly those associated with language, make up a running dialog about all of this as it is going on; this is your consciousness.
Those concepts aren’t too difficult to grasp, but people think of neuroscience as hard. And why? Because in order for your nervous system to perform these functions, it takes 100 billion neurons and a quadrillion connections structured over billions of years of evolution and all the human years of development and learning that resulted in who you are and where you are now.
You need to know three things to understand how the nervous system works. The first is how the neurons themselves work. The second is how neurons talk to each other in neural circuits. The third is how neural circuits form a particular set of functional modules in the brain. The particular set of modules that you have make you human. The content of your specific modules make you, you.
Our nearest animal relative, the chimpanzee, has pretty much the same neurons and neural circuits that you and I do. They even have most of the same modules. We humans have a few extra modules that permit consciousness. Understanding this is what this book is about.
About This Book
Let’s face it. Neuroscience is a complex topic. How could it not be since it deals with the brain, the most complex structure in the known universe and
Neuroscience For Dummies
the heart — if you don’t mind mixing a few body parts — of the nervous system. But in this book, I explain some very complex ideas and connections in a way that both students enrolled in introductory neuroscience courses and those who are just interested in the topic for fun can understand.
To use and understand this book, you don’t have to know anything about the brain except that you have one. In this book, I cover as much of the basics as possible with simple language and easy-to-understand diagrams, and when you encounter technical terms like anterior cingulate cortex or vestibulospinal reflex, I explain what they mean in plain English.
This book is designed to be modular for the simple reason that I want you to be able to find the information you need. Each chapter is divided into sections, and each section contains information about some topic relevant to neuroscience, such as
✓ The key components of the nervous system
✓ How neurons work and what the different kinds of neurons are
✓ What systems are involved in planning and executing complex actions
✓ The role of the neocortex in processing thoughts
The great thing about this book is that you decide where to start and what to read. It’s a reference you can jump into and out of at will. Just head to the table of contents or the index to find the information you want.
Note: You can use this book as a supplemental text in many undergraduate courses because I discuss the neuron and brain function as a system. Typical undergraduate perception courses, for example, give short (and usually unsatisfactory) introductions to neurons and neural processing and little if any coverage of cognition. Cognitive psychology and neuroscience courses typically cover cognition well but often don’t ground cognition at the level of neurons. Behavioral neuroscience courses sometimes ignore cognition and neurophysiology almost altogether while doing a decent job explaining heuristics and phenomenology of behavior and learning. You can also use this book as an adjunct to graduate or health profession courses where the nervous system or mental illnesses or disorders are mentioned but little explicit coverage is given of the nervous system and the brain.
Conventions Used in This Book
To help you navigate through this book, I’ve set up a few conventions:
✓ Italic is used for emphasis and to highlight new words or terms that are defined.
✓ Boldfaced text indicates the action part of numbered steps and the keywords or phrases in bulleted lists.
✓ Monofont is used for Web addresses.
What You’re Not to Read
What you’re not to read is whatever you don’t want to read or don’t need to read. Because this book is modular and headings clearly indicate what each section is about, you can go right to the appropriate section and bypass the others at whim. In addition, I don’t assume you have any particular prior knowledge about biology or neuroscience, so each topic starts with the basics and works up to more complicated explanations. If you do know a lot about neurons or brain anatomy, you can skip some of the early chapters and head right to the later ones that deal with major brain systems. If you’re just curious and really want to skip most of the details, you can go to the last four Part of Tens chapters and get a very brief overview of brain organization, function, and future developments that are likely to occur in neuroscience and the treatment of neural and brain disorders.
In addition, sidebars (text in the shaded box) and paragraphs marked with Technical Stuff icons are “skippable” — that is, they contain nonessential info that, while interesting, you can ignore without impairing your understanding of the topic at hand. Typical nonessential info includes discussions that explain some of the behind-the-scenes details that you may (or may not) be interested in, or interesting historical notes about early ideas in neuroscience.
Foolish Assumptions
In writing this book, I made some assumptions about you. To wit:
✓ You’re not a professional neuroscientist or neurosurgeon but may be a beginning student in this field. (If you notice that your neurosurgeon thumbing through a copy of this book before removing parts of your brain, you might want to get a second opinion.)
✓ You’re taking a course that relates to brain function, cognition, or behavior and feel that you would do better if you had a firm grasp of the how the nervous system and its components work.
✓ You want information in easy-to-access and easy-to-understand chunks, and if a little humor can be thrown in, all the better!
If you see yourself in the preceding points, then you have the right book in your hands.
How This Book Is Organized
To help you find information that you’re looking for, this book is divided into five parts. Each part covers a particular topic related to neuroscience and contains chapters relating to that part.
Part I: Introducing Your Nervous System
In Part I, I explain the overall structure of the brain and nervous system and how its component neurons function. Chapter 1 gives an overview of neuroscience, including some of the methodology used to study the nervous system and how it is evolving. Chapter 2 gives an overview of the brain, spinal cord, and peripheral nervous systems, including major modules and some fiber tracts. Chapter 3 is an introduction to neurons, the all-important universal components of the nervous system.
Part II: Translating the Internal and External World through Your Senses
How the various senses work is the subject of Part II. Chapter 4 treats the skin senses, from receptors to cortical processing. Chapter 5 covers the visual system starting at photoreceptors and tracing the visual signal through numerous brain areas that process this sense. Chapter 6 does the same for the auditory system. Taste and smell are the subject of Chapter 7. These chapters give an overview of many of the topics that would be the subject of a college perception course.
Part III: Moving Right Along: Motor Systems
Movement and motor control are treated in Part III. Just as the sensory system can be covered from receptor to high-order cortical processing, the motor system can be looked at as a hierarchy from muscle and motor neuron, to spinal reflex and pattern generator circuits, to cortical motor control, to frontal and prefrontal planning and execution. I cover movement basics in Chapter 8. Chapter 9 deals with spinal cord level coordination and its communication with the brain stem and higher centers. Chapter 10 takes up the cortex and action planning and sequencing. Chapter 11 deals with unconscious aspects of neuronal processing associated with behavior.
Part IV: Intelligence: The
Thinking Brain and
Consciousness
Part IV covers the big enchiladas: intelligence, thought, and consciousness. Chapter 12 discusses what intelligence is and why we may have it. How the brain processes thoughts is covered in Chapter 13. The executive brain, as a hierarchy of controllers, is the subject of Chapter 14. Chapter 15 discusses neural aspects of learning and memory. Chapter 16 treats plasticity in the brain and development. Chapter 17 covers neural dysfunctions, mental illness, and drugs that affect the brain.
Part V: The Part of Tens
In this part, I offer you a condensed overview of important and interesting facts, discoveries, and ideas about the brain. Chapter 18 in surveys ten crucial brain areas and what they do. Knowing just these ten might allow you to strike up or follow a conversation if you find yourself suddenly surrounded by neuroscientists in your favorite tavern (which is generally where we neuroscientists like to hang out). Chapter 19 gives a concise explanation of how neurons can do what they do. Chapter 20 lists ten amazing facts about the brain, providing sure bet winning material from reading only a few pages. Chapter 21 surveys promising and some possibly not-so-promising treatments and brain modification technologies coming in the near future.
Icons Used in This Book
The icons in this book help you find particular kinds of information. They include the following:
Looking at things a little differently or thinking of them in a new way can make potentially confusing concepts easier to understand. Look for this icon to find these “think of it this way” types of discussions.
This icon appears next to key concepts and general principles that you’ll want to remember.
In a subject as complicated as neuroscience, it’s inevitable that some discussions will be very technical. Fortunately for you, you don’t need to know the detailed where- and whyfors, but I include this info anyway for those who are voraciously curious or gluttons for punishment. Read or skip paragraphs beside this icon at will.
Neuroscience For Dummies
Over the ages, a lot of myths have sprung up about the brain and how its functioning impacts behavior, movement, psychological states, and more. This icon highlights those misunderstandings.
We wouldn’t know what we know about how the brain works without the diligent work of scientists and researchers who asked important questions and sought the answers. Look for this icon to find information about key studies or observations that profoundly affected what people now know about the brain and its function.
Where to Go from Here
Finally, the purpose of this book is to get you up to speed fast in understanding neurons and the nervous system, particularly the brain, but there are many important neuroscience topics that fall well beyond the scope of this book. Here’s just a sampling: intra-neuronal metabolism and second messenger cascades, association of neurological deficits with lesions in specific tracts and nuclei, traditional learning theory, and modern genetics. You can find detailed discussion of most of these subjects in Kandel, Schwartz, and Jessel’s Principles of Neural Science, 4th Edition (McGraw-Hill, 2000), the bible of neuroscience books.
Part I Introducing Your Nervous System
In this part . . .
We use many things that we don’t understand entirely; elevators, cars, and computers are just a few examples. The brain (and the rest of the nervous system) is surely at the top of this list because it is the seat of understanding itself.
In this part, I introduce you to the nervous system, covering its main divisions and how the neurons that compose it work. You won’t be ready to start a neurosurgery residency after you finish Part I, but you’ll have a good idea how your brain is put together and what the various parts do.
In This Chapter
Chapter 1
A Quick Trip through the Nervous System
▶ Following the evolution of the nervous system
▶ Understanding how the nervous system works
▶ Listing the basic functions of the nervous system
▶ Looking at types of neural dysfunction
▶ Peeking into neuroscience’s future contributions
T“My brain: it’s my second favorite organ.”
—
Woody Allen (Sleeper, 1973)
he brain you are carrying around in your head is by far the most complicated structure known in the universe, and everything you are, have been, and will be arises from the activity of this three-pound collection of 100 billion neurons.
Although this book is about neuroscience, the study of the nervous system, it’s mainly about the brain, where most of the nervous system action takes place, neurally speaking. If your brain functions well, you can live a long, happy, and productive life (barring some unfortunate circumstances, of course). If you have a brain disorder, you may struggle to overcome every detail of life, a battle that will take place within your brain. So read on for an introduction to the nervous system, how it works, what it does, and what can go wrong.
Understanding the Evolution of the Nervous System
The earth formed 4.5 billion years ago. Evolutionary biologists believe that single-celled prokaryote life (cells without a cell nucleus) appeared on earth
Part I: Introducing Your Nervous System
less than one billion years after that. What’s remarkable about this date is that geophysicists believe this was the earliest point at which the planet had cooled enough to sustain life. In other words, life appeared almost the instant (in geological time) that it was possible.
For unknown reasons, it took more than another billion years for eukaryotic life (cells with nuclei) to appear, another billion years for multicellular life to evolve from eukaryotic cells, and another billion years for humans to appear — which we did less than a million years ago. The processes that lead to multicellular life all took place in the earth’s oceans.
Specializing and communicating
In multicellular organisms, the environment of cells on the inside of the cell group is different from the environment of the cells on the outside of the group. These different environments required the cells in these multicellular life forms to develop a way to specialize and communicate. Understanding this specialization is one of the keys to understanding how the nervous system works.
Imagine a ball of a few dozen cells in a primitive ocean billions of years ago. Because these cells aren’t exposed to the seawater, those on the inside of the ball might be able to carry out some digestive or other function more efficiently, but they don’t have any way to get the nutrients they need from the seawater, and they don’t have a way of ridding themselves of waste. To perform these tasks, they need the cooperation of the cells around them.
For this reason, multicellular life allowed — in fact, mandated — that cells specialize and communicate. Eukaryotic cells specialized by regulating DNA expression differently for cells inside the ball of cells versus those on the outside. Meanwhile, some of the substances secreted by cells became signals that other cells responded to. Cells in multicellular species began specializing and communicating.
Moving hither, thither, and yon — in a coordinated way
Currents, tides, and waves in Earth’s ancient oceans moved organisms around whether they wanted to be moved or not. Even organisms specialized for photosynthesis developed buoyancy mechanisms to keep themselves in the upper layer of the ocean where the sunlight is.
Some multicellular organisms found an advantage in moving more actively, using flagella. But moving flagella on different cells on different sides of a
