By Kristen Yu
Published on Wednesday, April 25, 2012
Brain activity in response to visual representations of food and sexual activity can predict patterns of dietary and sexual behavior, according to a study conducted by Dartmouth psychology professors Todd Heatherton and Bill Kelley in conjunction with Kathryn Demos, a psychology and human behavior professor at Brown University. The study, published in the Journal of Neuroscience on April 18, compares activity levels in the reward center of the brain, known as the nucleus accumbens, with the changes in weight and sexual activity levels of 58 female Dartmouth freshmen over a period of six months, Kelley said.
The researchers found that higher levels of activity in the nucleus accumbens in response to images of food correlated with an average weight gain of approximately seven pounds, Heatherton said. Similarly, higher levels of activity in the nucleus accumbens in response to the images of people engaging in sexual behavior were correlated with greater reported sexual desires, he said.
Prior research indicating that college freshmen, particularly females, are likely to gain weight during their first year affected the team’s decision to use only freshman women in this study.
“We chose freshmen particularly because we could potentially see variability in terms of weight gain and sexual activity,” Demos said. “We were kind of capitalizing on the whole ‘Freshman 15.’”
The nucleus accumbens region was targeted due to its established role as the major reward center of the brain, according to Kelley.
“It’s a hub of the dopaminergic reward system in the brain,” Demos said. “Going back to old studies of animals and rewards, it’s the same area of the brain that would show increased activity to things like cocaine and rewarding drugs like that in animals.”
Participants were recruited and weighed for the study within a month of arriving at the College. Functional magnetic resonance imaging technology was then used to scan their brains as they viewed images of food, landscapes, buildings, people engaging in sexual activity and people drinking alcohol, according to Demos.
The subjects were tasked with pressing a button every time they detected a person present in an image. The tests were aimed at measuring “automatic responses to environmental cues,” focusing on rapid responses rather than extensive evaluations of the images, Heatherton said.
Six months later, participants were re-weighed and asked to complete two surveys about their sexual activity and desire. The team focused on eating behavior and sexual activity to study reward and self-regulation processes.
“Everyone has to eat, but people will try to self-regulate their eating behavior,” Heatherton said. “This provides us with a model for studying the reward system and how it can be controlled.”
Due to “material specificity,” the activity of the nucleus accumbens had to be specific to the visual cues in order to predict behavior, according to Kelley. Participants who exhibited higher levels of nucleus accumbens activity only in response to food cues, for instance, gained weight but were not more sexually active, he said.
“Having an overactive nucleus accumbens does not necessarily indicate a weight gain,” Kelley said. “The individual responses are correlated with particular behaviors.”
The scientists also observed that the participants’ self-described food preferences were not correlated with their brains’ responses to seeing those foods, Heatherton said.
“These things were happening without people knowing it, so you don’t know when your brain is more active to something and when it’s not,” Demos said. “It’s interesting that we know this because then we can work on things that are under more conscious control, like self-control and self-regulation.”
Because responses to reward cues are automatic, individuals must exert conscious self-control to regulate behavior, according to Heatherton. By studying the process of self-regulation, scientists can better understand the circumstances under which self-control fails.
“Understanding that there are individual differences that underlie weight gain can really help us develop more effective treatments in the form of behavioral interventions,” Demos said.
The ability of scientists to predict behavior through measurements of brain activity by linking fMRI results with behavior outside the scanner is innovative, neuroscience major Jesse Gomez ’12 said.
“It’s fascinating to think we’re arriving at the point in neuroscience where we can put someone in a scanner, measure brain activity and predict their actual behavior,” Gomez said. “The approach they used — measuring the strength of the connection between these frontal regions and reward centers with simple stimuli like images of people and food, and correlating that strength with other behaviors like dieting consistency — was pretty novel.”
Heatherton and Kelley plan to continue their research on self-regulation to establish why some individuals are better at self-regulating than others, as well as to consider the lessons that can be learned from changes accompanying these brain processes, Kelley said.