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Hungry Humans React Like Pavlov's Dogs

Scientific American

Most people would probably consider their tastes more discerning than those of the family pet. But according to new research, humans can be trained to crave food in a manner reminiscent of Pavlov's dogs. The findings, published today in the journal Science, may help scientists better understand compulsive eating disorders and substance addiction.

Russian scientist Ivan Pavlov conditioned his dogs to associate the sound of a bell with food. Eventually, the animals would drool in response to a ring, even when no reward was available. Jay A. Gottfried and his colleagues at the Wellcome Department of Imaging Neuroscience trained people undergoing brain scans to link abstract images on a computer scene with either the smell of vanilla or peanuts. After an eight-minute training period, the subjects showed heightened levels of activity in areas known to be part of the brain's reward circuitry, the amygdala and the orbitofrontal cortex (OFC), associated with the pictures alone. The researchers then instructed the patients to eat as much vanilla ice cream or peanut butter sandwiches as they desired, without becoming uncomfortably full. When the participants were retested using the MRI machine, the scientists found that the image associated with the food they had just eaten evoked a lower response than it did before the snack. The images linked to the other food, in contrast, continued to trigger a hunger response.