Researchers at Brookhaven National Laboratory have found that the mere sight of food triggers a release of dopamine, a pleasure chemical, making it difficult for us to pass up a good meal. Psychiatrist Nora Volkow asked a group of subjects to fast for up to 20 hours, then let them see and smell but not eat the foods they loved. Meanwhile, she used PET scans to measure dopamine levels in the subjects' brains. The greater the person's desire for food, the more dopamine was present. Surprisingly, the chemical was concentrated not in the brain's pleasure center but in a more primal region associated with habituation and probably with the compulsion to eat. "It's natural that our brains would create a mechanism to eat food when it was in front of us because it might not always be available," Volkow says. But now that food is everywhere, starvation is less of an issue than overeating. "The brain has not evolved as quickly as civilization, which has resulted in a maladapted response. You eat when you are not supposed to be eating," she says.