Distinct vestibular effects on early and late somatosensory cortical processing in humans
In non human primates several brain areas contain neurons that respond to both vestibular and somatosensory stimulation. In humans, vestibular stimulation activates several somatosensory brain regions and improves tactile perception. However, less is known about the spatio temporal dynamics of such vestibular somatosensory interactions in the human brain. To address this issue, we recorded high density electroencephalography during left median nerve electrical stimulation to obtain Somatosensory Evoked Potentials (SEPs) We analyzed SEPs during vestibular activation following sudden decelerations from constant velocity (90deg/s and 60deg/s) earth vertical axis yaw rotations and SEPs during a non vestibular control period. SEP analysis revealed two distinct temporal effects of vestibular activation: An early effect (28 32ms post stimulus) characterized by vestibular suppression of SEP response strength that depended on rotation velocity and a later effect (97 112ms post stimulus) characterized by vestibular modulation of SEP topographical pattern that was rotation velocity independent. Source estimation localized these vestibular effects, during both time periods, to activation differences in a distributed cortical network including the right postcentral gyrus, right insula, left precuneus, and bilateral secondary somatosensory cortex. These results suggest that vestibular somatosensory interactions in humans depend on processing in specific time periods in somatosensory and vestibular cortical regions.
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