EPV 4. Contra- and ipsilateral pathway-dependent cortical connectivity mapping of the vestibular network

Abstract

Introduction Crossing and non-crossing vestibular brainstem fibers provide a rope-ladder system for the bilateral central vestibular network ( Dieterich and Brandt, 2015 ). However, the processing of vestibular information within the human cortex is still poorly understood ( Lopez and Blanke, 2011 ). Aim of this study was to investigate said pathways by means of DTI (diffusion tensor imaging) based on the ipsi- or contralateral pathways found in a recent study using structural and functional connectivity mapping ( Kirsch et al., 2015 ). Methods Twenty-one healthy volunteers (10 females; aged 20–47 years, mean age 27.3 ± 4.9 years) were measured in a 3 Tesla MRI (Erlangen, Siemens, Verio). The data was analyzed with FSL. For the examination of the contra- and ipsilateral pathway-dependent cortical connectivity mapping of the vestibular network we calculated voxelbased DTI tractography between the vestibular nuclei and ipsilateral and contralateral cortical regions using the Juelich histological (cyto- and myelo-architectonic) atlas. Results At group level the data-driven DTI tractography showed distinct contra- and ipsilateral pathway-dependent cortical connectivity mapping of the vestibular network. Interestingly the ipsilateral pathways not only projected to more cortical regions but also the signal intensity was significantly higher in ipsilateral pathways when compared to contralateral pathways regardless of which level of crossing (pons or midbrain). Ipsilateral pathways primarily projected to the operculum 2, posterior insula, BA 1, 2, 3 and 4, superior parietal lobule, lateral geniculate body amygdala and hippocampus. Contralateral pathways projected primarily to the BA 6 and the anterior intraparietal sulcus. Discussion The data confirm a bilateral central vestibular network that is “informed” through a rope-ladder system of crossing and non-crossing vestibular brainstem fibers from both vestibular nuclei. However, the ipsilateral fibres seem to be more crucial and linked to the known multimodal cortical vestibular network ( Guldin et al., 1992 ). This supports results of earlier PET- and fMRI-studies with caloric and galvanic stimulation in humans ( Dieterich and Brandt, 2008 ). The contralateral fibres were fewer and seemed to be primarily linked to perceptual-motor planning and coordination or visual attention.