Vestibular Processing and its Cortical Signature in Humans

The vestibular system encodes rotations and translations of the head in space. While much is known about cortical processing of the classical Aristotelian sensory modalities, such as vision and touch, knowledge of how vestibular stimulation is encoded in the human brain is lacking, probably due to the inherent technical difficulties of recording human brain function while providing natural vestibular stimulation. Here, I used electroencephalography (EEG), psychophysics, and a custom-built rotating chair to elucidate how natural vestibular stimulation is encoded and processed in the brain, and identified novel markers of vestibular processing in the brain in the frequency domain. Specifically, in one set of experiments the spectral response to rotations were analyzed during constant velocity stimulation and short, transient stimulations in healthy subjects and bilateral vestibular-loss patients (BVPs). In another set of experiments the time course of spectral modulations was compared to that of the vestibulo-ocular response (VOR), which decays exponentially during constant velocity rotational stimulation with a time constant of 10-30s. Throughout all EEG experiments, spectral power in the alpha (8-13 Hz) band was found to consistently encode vestibular stimulation. Furthermore, the multisensory nature of the vestibular system was studied statistically by using a Bayes-optimal integration model to better understand how visual and vestibular information are combined in the brain to form a percept. Results across these experiments indicate that visual and vestibular information are not just integrated optimally, but also “fused” at the perceptual level.