Changes in brain activity after a diet-induced obesity.

Compared to lean subjects, obese men have less activation in the dorsolateral prefrontal cortex, a brain area implicated in the inhibition of inappropriate behavior, satiety, and meal termination. Whether this deficit precedes weight gain or is an acquired feature of obesity remains unknown. An adult animal model of obesity may provide insight to this question since brain imaging can be performed in lean vs. obese conditions in a controlled study. Seven diet-induced obese adult minipigs were compared to nine lean adult minipigs housed in the same conditions. Brain activation after an overnight fasting was mapped in lean and obese subjects by single photon emission computed tomography. Cerebral blood flow, a marker of brain activity, was measured in isoflurane-anesthetized animals after the intravenous injection of 99mTc-HMPAO (750 MBq). Statistical analysis was performed using statistical parametric mapping (SPM) software and cerebral blood flow differences were determined using co-registered T1 magnetic resonance imaging (MRI) and histological atlases. Deactivations were observed in the dorsolateral and anterior prefrontal cortices in obese compared to lean subjects. They were also observed in several other structures, including the ventral tegmental area, the nucleus accumbens, and nucleus pontis. On the contrary, activations were found in four different regions, including the ventral posterior nucleus of the thalamus and middle temporal gyrus. Moreover, the anterior and dorsolateral prefrontal cortices as well as the insular cortex activity was negatively associated with the body weight. We suggested that the reduced activation of prefrontal cortex observed in obese humans is probably an acquired feature of obesity since it is also found in minipigs with a diet-induced obesity.