Areas of the brain responsible for addictions and eating disorders are now identified, according to a team of U.S. and Canadian neuroscientists.
Dana Small, assistant professor of neurology at Northwestern University Medical School, and colleagues used positron emission tomography scans to measure brain activity in people eating chocolate.
They 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.
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.
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."
The scientists 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.
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.