Is vestibular function related to human hippocampal volume?

Abstract

INTRODUCTION: Recent studies implicate the effect of vestibular loss on cognitive decline, including hippocampal volume loss. As hippocampal atrophy is an important biomarker of Alzheimer′s disease, exploring vestibular dysfunction as a risk factor for dementia and its role in hippocampal atrophy is of interest. METHODS: Hippocampal and whole-brain MRI volumes were compared in adults aged between 55 and 83 years: (1) to substantiate previous literature, bilateral vestibulopathy (BV) was compared to healthy controls, (2) to correct for a potential confounding effect of concomitant hearing loss, BV was compared to healthy controls matched on age, sex, and hearing status, (3) to additionally evaluate the isolated effect of hearing loss on brain structure, sensorineural hearing loss (SNHL) was compared to healthy controls. Furthermore, to delineate otolith influence on hippocampal volume in preserved vestibular function (healthy controls and SNHL combined), saccular function was investigated. RESULTS: Whole-brain and targeted hippocampal approaches using volumetric and surface-based measures yielded no significant differences in either of three comparisons: (1) BV versus controls, (2) BV versus matched controls, and (3) SNHL versus controls. Binary support vector machines were unable to classify inner ear health status above chance level. Otolith parameters were significantly associated with hippocampal volume in preserved vestibular function. CONCLUSION: No significant differences in whole-brain or hippocampal volume were found when comparing BV with healthy controls, nor did concomitant SNHL confound this relationship. Otolith function may be associated with hippocampal volume rather than lateral semicircular canal integrity. Future BV studies should generally incorporate otolith function testing.