The findings by Vanderbilt University computational neuroscientist David Noelle and his colleagues were published in the May 17, 2005, issue of the Proceedings of the National Academy of Sciences.
"This model is the first to offer an explanation of how the neural circuits that allow us to apply rules and strategies to new situations develop," Noelle, assistant professor of computer science and psychology, said. "Our model provides an account of how the special properties of certain brain systems combine with life experiences to allow us to apply what we have learned to new situations. This account sheds light on why this ability sometimes fails, and on how brain damage can impact this ability."
The computer model is also the first of its kind capable of completing a variety of tests commonly used to determine if a patient has suffered injury to the frontal lobes of the brain. When inflicted with simulated damage, the model exhibited behaviors seen in people with frontal lobe damage.
"This computer model can provide insight into what causes the self-control deficits seen in individuals with damage to the frontal lobe," Noelle said. "An even more exciting prospect, which we are just beginning to explore, is the possibility that the model will help us understand the neural basis of developmental disorders involving flexible cognitive control, such as ADHD and autism spectrum disorders."
Researchers have known for some time that cognitive control, which is our ability to respond in an appropriate way even when faced with strong impulses to do otherwise, appears to depend on a brain area known as the prefrontal cortex. It is also known that the prefrontal cortex develops slowly compared to other brain areas and only matures late in adolescence.
The computer model developed by Noelle and his colleagues offers the first detailed explanation of how the special properties of the prefrontal cortex allow it to learn from life experiences and to flexibly identify appropriate rules, goals and intentions and apply them in new situations.
"Our model provides an account of how nature, in the form of specific neurobiological mechanisms, and nurture, in the form of breadth of experience, interact to produce flexible self-control," Noelle said.
The use of computer simulation methods allowed Noelle and his colleagues to examine hypothetical cases that cannot be ethically investigated in the laboratory, such as removing the special physiological properties of prefrontal neurons or grossly limiting the range of experiences provided during development. These analyses revealed that prefrontal neural specializations and exposure to tasks that require the extended exercise of cognitive control are both necessary for the proper development of prefrontal cortex. When either was absent, the model became inflexible - it could not apply rules or strategies to situations that differed from the ones present when it originally learned the rules or strategies.
The model also offers additional information about why the prefrontal cortex takes so long to mature.
"Since the prefrontal cortex imposes control on other brain areas, those other areas must stabilize before the prefrontal cortex can learn how to control them," Noelle said. "Our computer simulation results show the simulated prefrontal cortex maturing only after other interacting brain systems mature."
Noelle is a member of the Vanderbilt Center for Integrative and Cognitive Neuroscience. His co-authors on this research were Nicolas Rougier and Randall O'Reilly, University of Colorado; Todd Braver, Washington University; and Jonathan Cohen, Princeton University. The work was supported by the Office of Naval Research Grants and the National Institutes of Health.