Abstract
Introduction: The hypothalamus is a small (approximately 1 cm3) structure important for the autonomic functions, and it contains numerous nuclei that implement different autonomic functions. However, due to its size, the precise functional architecture of the human hypothalamus is not well understood. In the present study, we utilized areal parcellation to discriminate individual nuclei in the human hypothalamus based on areal profiles of resting state functional connectivity by using functional MRI.
Methods: We collected high-resolution functional MRI images (1.25 mm cubic voxel) from twelve healthy human subjects using multi-band EPI (Siemens Skyra 3-T MRI scanner), and parcellated the hypothalamus (Figure-1). Analytical details of areal parcellation are described in Osada et al. (2017) 1). The parcellation method based on resting-state functional MRI has successfully delineated many functional areas in the cerebral cortex based on the changes in the spatial pattern of functional connectivity in the cerebral cortex when a seed point is moved from one voxel to another 2)-5). In the present study, we extended such cortical parcellation methods, which have been applied to the 2D cortical surface, to the hypothalamus, a 3D structure, and the centers of parcellated areas in the hypothalamus were detected as hypothalamic foci.
Results: Ten bilateral pairs of foci were detected that were expected to represent hypothalamic nuclei, including the ventromedial hypothalamic nucleus (VMH), the arcuate nucleus (ARC), and the lateral hypothalamic area (LHA). The locations of the detected foci were consistent with those of the hypothalamic nuclei identified in a previous study 6), in which hypothalamic nuclei in structural MRI images were validated using histological images. The regions of interest (ROI) analyses revealed contrasting activity changes following glucose ingestion: decrease in the VMH and increase in the LHA in parallel with blood glucose increase (p<0.001, two-way ANOVA, interaction, factor: foci [VMH and LHA]×conditions [glucose and water]). Furthermore, decreased activity in the ARC significantly predicted future increase in blood insulin during the first 10 min after glucose ingestion (p<0.05, t-test)(Figure-2).
Conclusion: The hypothalamic nuclei can be putatively determined by the high-resolution 3D parcellation procedure. The results suggest that the analysis of the human hypothalamus at the nucleus-level can be used to reveal the diverse autonomic functions for future scientific and clinical investigations.
© 2018 The Juntendo Medical Society. This is an open access article distributed under the terms of Creative Commons Attribution License (CC BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original source is properly credited.
