The changes in brain metabolism in people with activated brown adipose tissue: a PET study

Brown adipose tissue (BAT) is a highly specialized thermogenic tissue and has profound effects on body weight, energy balance, and glucose metabolism. Body temperature regulation depends on the integrated activities of the autonomic nervous system, which is centered predominantly in the hypothalamus. The purpose of this study was to explore the interaction of brain and the activation of BAT by analyzing differences in brain metabolism between patients with and without activated BAT. Fluorodeoxyglucose (FDG) with positron emission tomography/computer tomography (PET/CT) was used to determine the activation of BAT and brain metabolism. After reviewing FDG PET/CT scans, we retrospectively collected 42 patients, 21 with activated BAT and 21 matched controls without activated BAT. We used the method of defining regions of interest (ROI) to examine differences in metabolism between their hypothalami and voxel (volumetric pixel)-based statistical parametric mapping to analyze the whole brain. Compared with controls, patients with activated BAT had a significant hypermetabolic area in the right inferior parietal lobule (Brodmann area 40) and significant hypometabolic areas in the left insula (Brodmann area 13) and right cerebellum; however, there were no metabolic differences in the hypothalamic regions. Our findings illustrate the close relationship of cold temperature exposure-triggered hypermetabolism in the right inferior parietal lobule and activated BAT. They also support the hypotheses that the insula and cerebellum regulate autonomic functions, which are important for controlling BAT thermogenesis within the central pathways.