P 27 Beyond binary parcellation of the vestibular cortex

Abstract

Introduction A binary approach to resting-state functional connectivity based parcellation (fCBP) provides useful insights into human brain organization, but also entails oversimplifications ( Glasser, 2016 ). This is especially true for multisensory and higher-level associative brain areas, such as the bilateral vestibular cortical network with its multiple multisensory areas ( Dieterich and Brandt, 2015 ). This study aimed to identify subunits of the vestibular cortex whilst accounting for a possible affiliation of voxel to different sensory systems using a multivariate fCBP within a vestibular region of interest (ROI) including known cortical areas of the vestibular network, i.e. vestibular informed masked fCBP. Methods Resting-state functional magnetic resonance imaging (fMRI) data of 60 healthy volunteers, 30 left-handed (LH; 14 females; aged 20–65 years, mean age 26.1 ± 8.6 years) and 30 age- and gender matched right-handed (RH; 17 females; aged 20–67 years, mean age 26.7 ± 8.3 years) was used to first perform a binary vmasked functional connectivity based parcellation (fCBP) within a vestibular ROI ( Lopez and Blanke, 2011 ). The subunits were then correlated (i) to each other and (ii) to whole-brain resting-state networks (RSN) and their behavioral interpretations ( Laird, 2011 ). Results Our approach revealed functional subunits, which were either “asymmetrical & less connected to RSN” (i.e. subunits within the inferior frontal gyrus (IFG; BA 44 & 45) and middle/posterior/inferior insula) or “symmetrical and more connected to RSN” (e.g. subunits within the superior temporal gyrus (STG) or temporo-parietal junction (TPJ)). Within these diverging subunits both “unique” voxels (= only present in 1 subunit) and “common” voxels (= part of multiple subunits) were distinguishable. Discussion The data confirm a complex handedness-dependent bilateral vestibular network of multiple multisensory areas organized around a core region in the inferior, middle, and posterior insula ( Dieterich, 2003 ). This core-region, whilst multisensory in nature, is hemisphere-dominant (asymmetrical) and functionally more specialized (less RSN-assigments). Its functional acolytes (e.g. STG, TPJ) surround it hemisphere-balanced (symmetrical), well-connected (more RSN-assigments), and functionally tinged by the neighboring sensory systems (e.g. TPJ by visual system, STG by auditory system). Within these fundamentally different types of units there seem to be more integrative (“common” voxels) and more disconnected (“unique” voxels) subunits.