Linking Vestibular Function and Subcortical Gray Matter Volume Changes in a Longitudinal Study of Aging Adults

Emerging evidence suggests a relationship between impairments of the vestibular (inner ear balance) system and alterations in the function and the structure of the central nervous system in older adults. However, it is unclear whether age-related vestibular loss is associated with volume loss in brain regions known to receive vestibular input. To address this gap, we investigated the association between vestibular function and the volumes of four structures that process vestibular information (the hippocampus, entorhinal cortex, thalamus, and basal ganglia) in a longitudinal study of 97 healthy, older participants from the Baltimore Longitudinal Study of Aging. Vestibular testing included cervical vestibular-evoked myogenic potentials (cVEMP) to measure saccular function, ocular VEMP (oVEMP) to measure utricular function, and video head-impulse tests to measure the horizontal semi-circular canal vestibulo-ocular reflex (VOR). Participants in the sample had vestibular and brain MRI data for a total of 1 (18.6%), 2 (49.5%) and 3 (32.0%) visits. Linear mixed-effects regression was used to model regional volume over time as a function of vestibular physiological function, correcting for age, sex, intracranial volume, and inter-subject random variation in the baseline levels of and rates of change of volume over time. We found that poorer saccular function, characterized by lower cVEMP amplitude, is associated with reduced bilateral volumes of the basal ganglia and thalamus at each time point, demonstrated by a 0.0714 cm³ ± 0.0344 (unadjusted p=0.038; 95% CI: 0.00397-0.139) lower bilateral-mean volume of the basal ganglia and a 0.0440 cm³ ± 0.0221 (unadjusted p=0.046; 95% CI: 0.000727-0.0873) lower bilateral-mean volume of the thalamus for each 1-unit lower cVEMP amplitude. We also found a relationship between a lower mean VOR gain and lower left hippocampal volume (β=0.121, unadjusted p=0.018, 95% CI: 0.0212-0.222). There were no significant associations between volume and oVEMP. These findings provide insight into the specific brain structures that undergo atrophy in the context of age-related loss of peripheral vestibular function.