The vestibulo-ocular reflex (VOR) generates smooth eye movements that are compensatory for head movements to ensure gaze stabilization during head rotations. The VOR is under adaptive control that corrects VOR performance when visual-vestibular mismatch arises during head movement. During normal visual-vestibular interaction, cooperation between the VOR and vision results in stabilization of the retinal image. Adaptive VOR recalibration occurs when a visual-vestibular mismatch arises through the manipulation of visual feedback during head movement or by lesion-induced modification of vestibular input. Considering how important VOR is in stabilizing gaze, one could predict that when VOR is lost, patients would be severely disabled by retinal image movement due to head movement. To compensate for vestibular deficits, the vestibular system uses other substitutes such as visual and somatosensory information for the lost vestibular signals. To investigate the contribution of somatosensory signal to the VOR, especially the semicircular-ocular reflex (ScOR), we examined the plasticity of the ScOR using vestibular-somatosensory interaction and the effect of the adaptive plasticity of the ScOR by somatosensory stimulation. We demonstrated a reasonably consistent effect on adaptation of ScOR gain using a somatosensory stimulation paradigm. Our data suggest that the ScOR and somatosensory signals share common neural pathways in such a way that a change in the synaptic efficacy of one pathway is accompanied by a change in the other. The role of a neural storage system that receives input from both the semicircular canals and the somatosensory system to maintain a spatial orientation is discussed.
