Cortical vestibular-evoked potentials depend on body orientation
Otolithic vestibular receptors encode linear acceleration and head orientation relative to gravity, providing a fundamental reference signal for perception, action, and higher-order cognitive functions. However, the cerebral dynamics of otolithic information processing and their sensitivity to body orientation remain poorly characterized. Here, we used sound-induced vestibular stimulation combined with electroencephalography (EEG) in human participants to characterize vestibular-evoked potentials (vEPs) and to examine how body orientation relative to gravity modulates these responses. Otolithic activation was validated using cervical vestibular-evoked myogenic potentials, confirming activation of otolithic pathways by 105 dB and 500 Hz tone pips. Acoustic stimuli included a novel masked stimulus that reduced auditory perception while preserving vestibular activation. Sound-induced vestibular stimulation elicited reliable short- and middle-latency vEP components. Importantly, middle-latency components Na/Pa (peak latency: 20-30 ms) and N*/P* (41-54 ms) were modulated by body orientation, showing reduced amplitudes in the supine compared with the upright position, but only for otolithic-activating sounds and not for matched auditory control stimuli. This orientation-dependent modulation was stronger for Na/Pa and was specific to otolithic-activating sounds, supporting a vestibular rather than auditory origin and highlighting early integration processes. This pattern suggests that modulation of vEPs primarily reflects context-dependent cerebral processing of otolithic signals rather than peripheral sensory mechanisms. Together, our results establish Na/Pa and N*/P* as reliable cerebral markers of otolithic processing and demonstrate that early cerebral vestibular responses are dynamically shaped by body orientation and postural context. NEW & NOTEWORTHYThis study identifies middle-latency vestibular-evoked potentials as reliable cerebral markers of otolithic information processing. We show that both Na/Pa and N*/P* are selectively modulated by body orientation for otolithic-activating sounds, but not for auditory controls. These findings reveal that early otolithic vestibular processing dynamically depends on bodily context, extending current models of multisensory vestibular integration.