Description
The hippocampus and the orbitofrontal cortex are associated with multiple functions including memory, learning, appetite regulation and reinforcement and reward. Hippocampal and orbitofrontal efferents can excite dopaminergic cells in the nucleus accumbens, a key structure in motivating rewarding behavior, via activation of the ventral tegmental area and striatum. It has been proposed that hippocampal input regarding stimulus salience, and orbitofrontal input about expected outcome, are integrated in the nucleus accumbens and are crucial for determining adaptive behavior responses. Malfunction of this network has been implicated in drug addiction, obesity and problems with executive functioning. The purpose of the present study is to investigate the role of hippocampal activation to sucrose and body mass index (BMI) within this system. This study uses cross-sectional, archival, functional imaging, structural imaging, neuropsychological and physical data, from 53 adults between 44 and 83 (M=59, S.E=1.5) years of age; 27 were classified as middle-aged and 26 were classified as old. Participants were scanned both with and without a nutritional preload (satiety and hunger) and instructed to rate the pleasantness of several taste solutions, including sucrose. This study focuses on data from functional imaging of hippocampal activation to sucrose collected from participants without a nutritional preload (hunger condition) and during pleasantness ratings. Cortical thickness measures of the orbitofrontal cortex were calculated using the FreeSurfer image analysis suite and neuropsychological data were obtained via administration of the Conner's Continuous Performance test, a measure of attention and impulsivity. Of the 53 participants, 23 fit the diagnostic criteria for metabolic syndrome and 30 were healthy controls, allowing for a wide range of BMI to be analyzed. BMI significantly predicted hippocampal activation while tasting sucrose, and hippocampal activation significantly predicted orbitofrontal cortex thickness, but only in middle-aged individuals. This supports the proposal of an aberrant hippocampal-orbitofrontal network involved in obesity, and further implicates abnormal taste processing of sucrose in this system. These results further highlight the necessity of studying and mitigating the negative health outcomes associated with high sugar intake, including its effects on cognition and aging.
