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16-05-2012 | Psychology | Article

Stimulation of satiety pathway in brain differs in anorexic versus obese women


Free abstract

MedWire News: Women with anorexia have an overstimulated and those with obesity an understimulated dopamine reward pathway in the brain in response to food intake, report researchers.

This suggests that the brains of anorexic patients may prompt them to stop eating earlier than normal, whereas obese individuals continue to feel hungry despite eating a sufficient amount of food.

"Food restriction and weight loss have been associated with heightened brain dopamine-related reward response in rodents," say Guido Frank (University of Colorado, Aurora, USA) and colleagues. "Over-consumption of food on the contrary showed addiction-like dopamine D2 receptor down regulation in rodents in brain reward regions."

Frank and co-investigators used blood oxygen level-dependent functional magnetic resonance imaging (MRI) to assess whether 21 underweight, restricting-type anorexia nervosa (AN) women (mean age 22.5 years) and 19 obese women (mean age 27.1 years) had brain alterations in response to food stimuli compared with 23 healthy control women (mean age 24.8 years).

The AN women had a mean body mass index (BMI) of 16.10 kg/m2, and the obese and control women a mean BMI of 34.67 and 21.49 kg/m2, respectively.

The women all underwent a reward-conditioning task where different strengths of sugar solution were associated with various visual stimuli.

"The task has been associated with activation of brain dopamine reward circuits, and it allows the comparison of actual brain response with expected brain activation based on established neuronal models," explain Frank and team.

As reported in Neuropsychopharmacology, the authors found that activation in the orbitofrontal cortex in response to the task differed between the three groups.

They found that areas in the anteroventral striatum, insula, and prefrontal cortex showed brain responses that were greater in the AN group than in controls. Conversely, responses in the same areas were lower in obese individuals than controls.

"It is clear that in humans the brain's reward system helps to regulate food intake," said Frank in a press statement.

However, he added that "the specific role of these networks in eating disorders such as anorexia nervosa and, conversely, obesity, remains unclear."

By Helen Albert

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