By measuring the mental activity of people eating chocolate, a team of US and Canadian neuroscientists has identified the areas of the brain responsible for addictions and eating disorders.

The research, reported in the journal Brain, was conducted by a team of scientists from the Northwestern University Medical School.

Dana Small, assistant professor of neurology, and colleagues were among the first scientists to examine the brain's activity using positron emission tomography in a bid to identify its response to changes in the perceived pleasantness of a food stimulus.

Small believes that certain regions of the brain register reward and that this is how people experience addictions. Pleasantness is thus a "primary reinforcer" of that reward, indicative of something anybody always enjoys and has liked from birth. Primary reinforcers can include addictive drugs or fat and sweet tastes.

The individuals' rating of pleasure in eating chocolate was associated through the experiments with increased blood flow in certain areas of the brain, particularly the orbital frontal cortex and midbrain. Brain scans have revealed that addictive drugs such as cocaine also activate these areas.

The scientists then gave 15 participants who considered themselves "chocoholics" between 40-170g to melt slowly in their mouths. From this, the researchers found that the areas of the brain stimulated changed as the individuals experienced the feeling of having eaten too much chocolate, when they began to perceive the sweet treat as aversive.

Despite being satiated, some people continued to eat the chocolate, and Small believes that their brain responses will provide an interesting comparative measure against those in people diagnosed with eating disorders.

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