Special Section: Department of Human Development and Family Studies
Individuality Matters Professor creates paradigm shift in the way researchers collect and analyze data on human subjects. Creating maps or models of brain connectivity—the complex relationships among the billions of neurons that are responsible for reason, memory, and emotion—eventually could lead to better understanding of the intricate information processing that underlies normal and deviant cognitive functioning and its development throughout the life span. Yet, creating models that estimate brain connectivity networks across people is difficult because no two brains are the same. “Brain connectivity models often are parameterized with data that have been collected from many people and then pooled across those people,” said Peter Molenaar, Distinguished Professor of Human Development and Family Studies and of Psychology. “But every person is unique, so using such methods gives spurious results.” Using a set of powerful theorems, known as ergodic theorems, Molenaar has come up with a way to account for the individual differences among people. Rather than pooling across individuals, he uses a person-specific approach wherein he closely examines just a few individuals and then builds models from that information. “One problem with this approach is that when you start by fitting individual models to individual subjects you get models all over the place,” said Molenaar. “If the goal of science is to come up with common laws, how do you bring commonality to a bunch of heterogeneous models? We’ve found a really good method to do that.” Molenaar joined the faculty at Penn State in 2005 after working as a professor for twenty-nine years at the University of Amsterdam. Since his arrival at Penn State, he and his former graduate student Katie Gates ’11g HDFS, and others, have applied the person-specific approach to the study of brain connectivity using the University’s functional magnetic resonance (fMRI) machine. Molenaar also has applied it to the study of electroencephalography (EEG) data, or electrical activity in the brain, as well as to electrodermal activity and heart rate. Molenaar said his person-specific approach can be applied to a variety of other problems as well, including the creation of nanotechnological devices that make continuous measurements of processes within our bodies and the optimization of instructional effort to meet the learning goals of individual students with the least possible effort and maximum enjoyment. One area in which he has done some work is in advancing the idea of an artificial pancreas. In their study, he and his colleagues monitored the blood-sugar levels of five people with type 1 diabetes, as well as their intake of insulin and carbohydrates. “We fitted to each individual patient a dynamic model, and based on that model we could predict with more than 90 percent fidelity what would be the blood glucose level of that particular patient one-half hour later,” said Molenaar. “So we have all the tools and ingredients necessary to create an artificial pancreas.” Molenaar explained that the way in which he conducted the study with diabetes patients is similar to the way in which he conducts
other studies using the person-specific approach—by using the same basic model type for all subjects, but obtaining the parameter values at the individual level. “You can make a chip and on that chip is a particular model,” he said. “You integrate the chip to the insulin pump of a patient; it takes say one day to tune itself to the patient, to adapt mathematically to him or her; and then it goes to work. So the generality is no longer at the lowest level of the data; it is at a higher level of the model.” Another area to which Molenaar has applied his person-specific approach is in psychotherapy. In 1987, he published a paper about a single patient who received sixty-two psychotherapy sessions. Molenaar took that information and fitted it to a time-series model, or a model containing data points collected at equally spaced time intervals. He concluded that time-series models are suitable for studying individual people and that results from such models can be used to build scientific laws that apply to larger populations. Molenaar said that his success in promoting the person-specific approach—which is disliked by some because of its newness, yet accepted by most because of its correctness—is timeliness. “We have on our side what Germans call the Zeitgeist, or the spirit of the times,” he said, “because medicine is going in the direction of personalized care and we have all these gadgets, like smartphones and nanotech devices, with which we can measure people almost continuously during their daily lives. Person-specific methodology is the future.”