Genetic Influences on Behavior

A pilot study of genetic and environmental influences on amygdala, orbital medial prefrontal cortex and dorsal anterior cingulate cortex activation: a twin study of fMRI
2007 Seed Grant
Kristen Jacobson, Ph.D.
The University of Chicago

 
Dr. Kristen Jacobson, an associate professor of psychiatry at The University of Chicago, has always been interested in environmental experiences and their effect on behavior, but thought there was something more to why people behave how they do.  It is easy to blame poor parenting, or the wrong peer group to explain why a child makes bad decisions.  But Dr. Jacobson wanted to show that sometimes we make choices – good and bad – because we are who we are.  And we are who we are, in part, because of our genetic make-up.
 
A twin design is a powerful way to examine the contribution of genes and environment on behavior.  Dr. Jacobson’s project, which was awarded a Brain Research Foundation Seed Grant, proposes to collect functional imaging data related to impulsivity and socioemotional information processing from adult twin pairs.  Twins will be subjected to impulsivity and emotional tasks in order to better understand the genetic factors behind neurophysiological response patterns that are related to the development of aggression and antisocial behavior.
 
This study will focus on three brain areas that underlie aggression and antisocial behavior: the amygdala (involved in fight-or-flight response), the orbital medial prefrontal cortex (OMPC) and the dorsal anterior cingulated cortex (dACC).  Sixteen sets of twins, 8 identical and 8 fraternal, will perform various tasks while whole-brain functional magnetic resonance imaging is carried out.  These performance tasks are well-established activities used to assess a person’s impulsivity and aggression.
 
In the first task, subjects are shown photographs of faces that illustrate varying degrees of emotion while brain images of the amygdala and OMPC are captured.  They are asked to rate the photographs emotion as positive, negative or neutral.  In addition to faces, they are also shown emotional pictures that display pleasant, neutral or unpleasant scenes (puppies, a snake, car accident, etc.).  People that exhibit aggressive behavior interpret these pictures differently.  For example, aggressive people are more likely to view neutral faces as hostile, compared to non-aggressive people.
 
Another task is called “Go/No-go” which looks at motor and cognitive impulsivity.  The mechanism behind impulsivity behavior is thought to be the dorsal anterior cingulate cortex (dACC). In this performance task, the subject views letters that are flashed on a computer screen as they are in the magnetic resonance scanner.  For example, the subject is told to press a button when they see a “red D,” but is not supposed to push the button for any other letter, including other colored “D’s.” This task is extremely hard for children with attention deficit hyperactivity disorder.  In fact, extremely impulsive kids can’t stop themselves from hitting the button repeatedly. In the scanner, Dr. Jacobson is able to see what the brain does when the correct answer flashes on the screen, and she can also see what happens in the brain before the button is pushed for the wrong letter.
 
The data obtained from these tasks will be combined with lab-based behavioral assessments and self-reports of aggression and antisocial behavior to determine whether the genetic factors that underlie individual differences in brain activation levels overlap with genetic influences on aggression and antisocial behavior. If in fact the way brains are wired and the way this information gets transmitted are heritable, identical twins’ brains should be more similar than fraternal twins’ brains, illustrating a genetic influence on brain pathways.
 
Using the data collected from her 2007 Seed Grant, Dr. Kristen Jacobson was able to turn this $25,000 grant into over $5.5 million in additional funding from the National Institutes of Health.