The cortical electrophysiological changes evoked by natural vestibular stimulation in healthy and bilateral vestibulopathy.

Peripheral vestibular stimulation elicits brainstem reflex responses manifesting as a vestibular-ocular reflex nystagmus ("VOR") and evokes a perception of self-motion or "vertigo." Although VOR responses are objectively measured via eye movements, no such objective measure exists for assessing the cortical vestibular processing of self-motion. Understanding how the brain encodes vestibular-mediated self-motion could provide electrophysiological markers for clinical syndromes where reflex and perception are uncoupled, e.g., in vestibular agnosia. Hence, here we investigated the brain's encoding of bottom-up vestibular signals, using passive yaw-plane chair rotations performed in complete darkness with simultaneous EEG. Healthy controls (n = 8) were compared with patients with bilateral vestibulopathy (BVP), either with residual function (BVP-residual; n = 6) or complete loss (BVP-complete; n = 1), at five acceleration levels (range: 30-150°/s2). Comparing healthy controls with BVP-residual, we found 1) no differences in time-frequency analyses and 2) differences in vestibular-evoked potentials magnitude (P < 0.01). Chair acceleration changes were consistently accompanied by phase-locked and induced (nonphase locked) theta increases as well as alpha reduction in both, healthy and patients. Importantly, while the induced theta component was present in BVP-residual, it was absent in BVP-complete. Overall, findings indicate potential utility of 1) vestibular-evoked EEG responses for identifying attenuated vestibular signaling and 2) theta activity as a cortical signature of preserved bottom-up vestibular signaling. These preliminary findings would require further investigation to confirm their functional role.NEW & NOTEWORTHY This study demonstrates that passive yaw rotation elicits cortical vestibular-evoked potentials and time-frequency changes in healthy individuals. Moreover, these responses are largely preserved in bilateral peripheral vestibulopathy patients with residual vestibular function. The degree of magnitude attenuation of evoked potentials can indicate the residual vestibular signals reaching cortex. Moreover, given the tight link between acceleration changes and theta-band activity, it has potential to be a key marker for assessment of cortical vestibular function.