WEDNESDAY, Oct. 10, 2001 (HealthDayNews) -- By scanning people eating chocolate, researchers say they may have identified specific areas of the brain that underlie addiction and eating disorders.
Chocolate is the single most-craved food in America, research has found. To explore that intense yearning, researchers from Northwestern University used positron emission tomography (PET) scans.
Dana Small, assistant professor of neurology at Northwestern's Medical School, in Evanston, Ill., and her colleagues gave 15 people, who classified themselves as "chocoholics," from 16 to 74 squares of chocolate, telling them to let each piece melt slowly in their mouths. The researchers measured brain activity as they became full and as they continued to eat beyond the point where they no longer wanted to.
When people said they were enjoying chocolate, the researchers found blood flow increased in the front areas of the brain and deep within it, the same areas activated by addictive drugs such as cocaine.
However, as the subjects continued to eat chocolate, they got to a point that they no longer wanted any more. As eating chocolate became unpleasant, the parts of the brain that were activated shifted to the side and further to the front, to the lateral orbital frontal cortex and the prefrontal cortex, areas that previous research has shown are associated with the decision to stop eating.
Small says people with eating disorders may have a skewed brain mechanism. She speculates that the brains of people who chronically overeat may take longer to decide that continued eating is unpleasant.
"This study suggests there are very different regions of the brain that process rewarding things versus punishing things. This is the first study to look at the brain's response to a really rewarding food," Small says.
The research is reported in the September issue of the journal, Brain.
Neurologists believe addictive drugs such as nicotine or heroin change the mechanism of the brain over time, leading to addiction. However, studying that mechanism is difficult because by the time the brains of addicts are studied, the changes already have occurred. "We are starting to uncover what the healthy brain looks like, so we have a baseline for comparison," Small says.
Whether chocolate is addictive, however, is debatable. Addiction, defined clinically, must lead to tolerance, meaning a person must consume more and more to have the same effect or suffer withdrawal symptoms, says David Zald, professor of psychology at Vanderbilt University in Nashville, Tenn.
People don't develop a tolerance for chocolate or become jittery and anxious when they don't eat it, Zald says.
"Chocolate is one of the most pleasurable tastes we know as humans," Zald says. "If we can understand how the brain processes things that are rewarding, we can begin to understand how the brain processes addiction."
The brain mechanism that causes the "diminishing returns" -- the first bite tastes best, but eating becomes progressively less rewarding until it becomes unpleasant -- probably is very important in controlling how much we consume, Zald says. Interestingly, the men in the study lost their motivation to eat chocolate more quickly than the women, hinting at possible gender differences in how eating disorders and addictions develop, he says.
"If we didn't have some diminishing returns, what would keep us from continuing to eat and eat and eat? It's an important mechanism," Zald says.
What To Do
Read about the history of chocolate at The Sweet Science of Chocolate.