Age-related decline in vestibulo-ocular reflex gain is associated with an increased sway response to electrical vestibular stimulation.

Despite considerable loss of peripheral vestibular input with age, there is relatively little change in function. This has led to speculation that increasing central neural gain mitigates such losses. Here we test this hypothesis by comparing the gain of the vestibulo-ocular reflex (VOR) with the response to electrical vestibular stimulation (EVS) across the lifespan. The VOR assesses the full vestibulo-motor pathway whereas EVS bypasses the peripheral vestibular mechanics. Hence, any dissociation between the two may reveal a difference in central versus peripheral function. A rotating chair was used to assess VOR gain in 62 participants aged 20-87 years. EVS-evoked postural sway responses were then tested in the same participants on the same day. We found a significant age-related reduction in VOR gain (r = -0.48, p < 0.001), an increase in EVS gain (r = 0.36, p = 0.004), and an inverse correlation between the two (r = -0.35, p = 0.006). The EVS response is consistent with an increase in central neural gain. We also observed an increase in VOR phase lead with age. This may impair VOR accuracy thus imposing limits on the extent of compensation, explaining why VOR gain declined with age. These results demonstrate partial neural compensation for age-related peripheral loss. However, the inverse correlation between VOR and EVS gain persisted even when age was factored out (r = -0.28, p = 0.031). This suggests a general property of the central nervous system whereby neural gain is tuned to match interpersonal differences in peripheral vestibular input.