6. fMRI (functional MRI: 磁気共鳴機能画像法) 前庭情報と空間識の皮質処理機構—fMRIによる知見—

概要

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Imaging studies in humans have confirmed the existence of several separate and distinct vestibular cortical areas, which had been identified earlier by tracer and electrophysiological studies in experimental animals. The most robust cortical vestibular structures in monkeys are the parieto-insular vestibular cortex (PIVC), the visual temporal sylvian area (VTS) in the retroinsular cortex, the superior temporal gyrus (STG), the inferior parietal lobule (IPL), the anterior cingulum, the hippocampus and area 6a. All belong to a multisensory vestibular cortical circuit. The PIVC seems to be a dominant multi-modal vestibular cortex area in monkeys and it is considered the ’core region’ within this network. During the last 10 years, many positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) studies using vestibular, somatosensory and visual optokinetic stimulation have revealed that such multisensory vestibular cortical areas are located in similar sites in humans. In addition, a reciprocal inhibitory cortical interaction has been observed between different sensory systems, such as the inhibitory visual-vestibular interaction. This interaction provides a powerful means for shifting the dominant sensorial weight from one modality to the other for resolving conflicts between incongruent sensory inputs. In this article, fMRI studies on cortical processing of vestibular sensation and spatial orientation were reviewed.