Clues in the Brain to Patterns of Eating

Differences in brain circuitry may help explain why one person develops anorexia nervosa (AN) and another becomes obese. Using functional magnetic resonance imaging (fMRI), Dr. Guido Frank and co-workers at the University of Colorado, Aurora, found that reward circuits in the brain were sensitized in anorexic women and desensitized in obese women. fMRI measures brain activity by detecting the changes in blood oxygenation and flow that occur in response to neural activity. When an area of the brain is more active, it consumes more oxygen to meet this demand and more blood flows to the active area and can be measured with fMRI scans.

Dr. Frank and colleagues studied 21 patients with restricting-type AN (mean age: 22 years), 19 obese patients (mean age: 27 years), and 23 healthy control women (mean age: 24 years) with fMRI and a reward-conditioning task Neuropsychopharmacology 2012; May 2. doi:10.1038/nnp.2012.51 [Epub ahead of print]). The participants were visually conditioned to associate certain shapes with either a sweet or a non-sweet solution, and then received the taste solution expectantly or unexpectedly.

Activity in the occipitofrontal cortex was found and used to differentiate all three groups. Brain reward circuits were more responsive to food stimuli in the women with AN but less responsive in the obese women. The authors found that during the fMRI sessions, an unexpected sweet-tasting solution led to increased neural activation of reward systems in the patients with AN and to diminished activation in the obese individuals and control group. In animal studies, food restriction and weight loss have been associated with greater dopamine-related reward in the brain. Although the mechanisms for the association is not yet known, the authors feel these brain reward response patterns could become biomarkers of the respective weight state. The findings also suggest that eating behavior is related to brain dopamine pathways involved in addictions.