Measuring brain activity in people eating chocolate offers new clues about how the body becomes addicted

August 28, 2001

CHICAGO --- Using positron emission tomography scans to measure brain activity in people eating chocolate, a team of U.S. and Canadian neuroscientists believe they have identified areas of the brain that may underlie addiction and eating disorders.

Dana Small, assistant professor of neurology at Northwestern University Medical School, and colleagues found that individuals' ratings of the pleasantness of eating chocolate were associated with increased blood flow in areas of the brain, particularly in the orbital frontal cortex and midbrain, that are also activated by addictive drugs such as cocaine.

According to an article on their research that appears in the September issue of the journal Brain, the neuroscientists also learned that the brain regions activated by eating chocolate when it is rewarding are quite different from those areas that are activated by eating chocolate when it is perceived as aversive (as a result of having eaten too much chocolate).

Small is conducting research on the brain regions involved in reward because of the role of reward in addiction. She believes this is the first study to look at the brain's activity in response to changes in the perceived pleasantness of a "primary reinforcer" -- in this case chocolate.

According to Small, a primary reinforcer is a stimulus that an individual doesn't have to learn to like but, rather, is enjoyed from birth. Addictive drugs can be viewed as primary reinforcers. Fat and sweet also are primary reinforcers, and chocolate is chock full of fat and sweet, Small said.

Many food scientists have reported chocolate to be the single most craved food. Some researchers have even argued that chocolate is addictive.

Small and her colleagues gave 15 study participants, who classified themselves as "chocoholics," between 16 to 74 squares of chocolate (or about 40 to 170 grams) that had to melt slowly in the mouth. The researchers measured brain activity of participants as they became full and then beyond full to the point where they ate despite no longer wanting to.

"In other words," Small said, "eating chocolate went from being a highly rewarding to a highly punishing activity."

Small and colleagues found that different brain regions were activated selectively depending on whether subjects were eating chocolate when they were highly motivated to eat and rated the chocolate as "very pleasant" or whether they ate chocolate despite being satiated.

Small explained that studying the brain's response to eating a highly rewarding food such as chocolate provides an effective "in-health" model of addiction. "The problem with studying addicts to understand addiction is that we don't know what their brains were like before the addiction and we therefore can't determine which brain functions have changed," Small said.

Small also noted that measuring brain responses in normal individuals who ate beyond satiety provided a measure against which the brain response to overeating in many people with eating disorders can be compared and thus serve as the basis for new research on eating disorders.
Small is a researcher in the Cognitive Brain Mapping Group at Northwestern University Medical School. Collaborating on this study were Robert J. Zatorre, Alain Dagher, Alan C. Evans and Marilyn Jones-Gotman, Montreal Neurological Institute, McGill University, Montreal, Canada.

KEYWORDS: Cognitive brain mapping, chocolate, addiction, reward, aversion behavior

Northwestern University

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