Identifying human parieto-insular vestibular cortex using fMRI and cytoarchitectonic mapping

The parieto-insular vestibular cortex (PIVC) plays a central role in the cortical vestibular network. Although this region was first defined and subsequently extensively studied in nonhuman primates, there is also ample evidence for a human analogue in the posterior parietal operculum. In this study, we functionally and anatomically characterize the putative human equivalent to macaque area PIVC by combining functional magnetic resonance imaging (fMRI) of the cortical response to galvanic vestibular stimulation (GVS) with probabilistic cytoarchitectonic maps of the human parietal operculum. Our fMRI data revealed a bilateral cortical response to GVS in posterior parieto-insular cortex. Based on the topographic similarity of these activations to primate area PIVC, we suggest that they constitute the functionally defined human equivalent to macaque area PIVC. The locations of these activations were then compared to the probabilistic cytoarchitectonic maps of the parietal operculum (Eickhoff et al. [2005a]: Cereb Cortex, in press; Eickhoff et al. [2005c]: Cereb Cortex, in press), whereby the functionally defined PIVC matched most closely the cytoarchitectonically defined area OP 2. This activation of OP 2 by vestibular stimulation and its cytoarchitectonic features, which are similar to other primary sensory areas, suggest that area OP 2 constitutes the human equivalent of macaque area PIVC.