Associations Between Vestibular Function and White Matter Microstructure in Healthy Older Adults.

The relationship between vestibular function and white matter (WM) integrity is poorly understood, despite increasing evidence linking vestibular sensory decline and motor and cognitive deficits in older adults. This study examined associations between vestibular function and the microstructural integrity of 19 WM pathways in 394 cognitively healthy participants aged 60+ from the Baltimore Longitudinal Study of Aging who had regional WM microstructure assessed by diffusion tensor imaging metrics: fractional anisotropy and mean diffusivity. The vestibular functions of the saccule, utricle, and horizontal semi-circular canal were assessed using the cVEMP and oVEMP tests and the vHIT, respectively. Multiple linear regression of WM metrics onto vestibular function, adjusted for age, sex, intracranial volume, and scanner type, was used to examine the association between WM and vestibular function. We found that higher canal function was associated with higher integrity in the external capsule, the cingulum projection to the hippocampus, the inferior fronto-occipital fasciculus, and the genu of the corpus callosum, but lower integrity in the limbs of the internal capsule, sagittal stratum, posterior thalamic radiation, the cingulum projection to the cingulate gyrus, and fornix. Utricular function was associated with higher integrity in the anterior limb of the internal capsule and the fornix but lower integrity in the retrolenticular limb of the internal capsule. Saccular function was not associated with WM microstructure. This study demonstrates for the first time potential associations between vestibular end-organ function and WM microstructure in healthy, older adults, with horizontal canal function exhibiting diffuse associations with multi-sensorimotor tracts, whereas utricular function shows more focal associations. Because these findings are concomitant with lower age-related WM integrity, they suggest that better vestibular function may confer resilience in certain pathways while potentially accelerating age-related degeneration in others. Longitudinal studies will be needed to robustly identify WM neuroimaging markers of aging-associated vestibular loss over time.