Differential brain responses to satiation in obese and lean men

Knowledge of how the brain contributes to the regulation of food intake in humans is limited. We used positron emission tomography and measures of reg ional cerebral blood flow (rCBF) (a marker of neuronal activity) to describ e the functional anatomy of satiation (i.e., the response to a liquid meal) in the context of extreme hunger (36-h fast) in 11 obese (BMI greater than or equal to 35 kg/m(2), age 27 +/- 5 years, weight 115 +/- 11 kg, 38 +/- 7 % body fat; mean +/- SD) and 11 lean (BMI less than or equal to 25 kg/m(2), age 35 +/- 8 years, weight 73 +/- 9 kg, 19 +/- 6% body fat) men. As in lea n men, satiation in obese men produced significant increases in rCBF in the vicinity of the ventromedial and dorsolateral prefrontal cortex and signif icant decreases in rCBF in the vicinity of the limbic/paralimbic areas (i.e ., hippocampal formation, temporal pole), striatum (i.e., caudate, putamen) , precuneus, and cerebellum. However, rCBF increases in the prefrontal cort ex were significantly greater in obese men than in lean men (P < 0.005). rC BF decreases in limbic/paralimbic areas, temporal and occipital cortex, and cerebellum were also significantly greater in obese men then in lean men ( P < 0.005), whereas rCBF decreases in the hypothalamus and thalamus were at tenuated in obese men compared with lean men (P < 0.05). This study raises the possibility that the brain responses to a meal in the prefrontal areas (which may be involved in the inhibition of inappropriate response tendenci es) and limbic/paralimbic areas (commonly associated with the regulation of emotion) may be different in obese and lean men. Additional studies are re quired to investigate how these differential responses are related to the p athophysiology of obesity.