Somatosensory induced adaptation in the human otolith-ocular reflex

Abstract

The vestibulo-ocular reflex (VOR) generates smooth eye movements that compensate for head movements to ensure gaze stabilization during head rotation. The VOR is under adaptive control and 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 visual-vestibular mismatch arises through the manipulation of visual feedback during head movement. In consideration of how important VOR is in stabilizing gaze, it could be predicted that when VOR is lost, patients would be severely disabled by retinal image movement due to head movement. The vestibular center uses substitutes such as visual and somatosensory information to compensate for lost vestibular signals. In the present study, to investigate the contribution of somatosensory signals to VOR, especially the otolith-ocular reflex (OOR), we examined the plasticity of the OOR using vestibular-somatosensory interaction and the effect of the adaptive plasticity of the OOR by somatosensory stimulation using alternative pressure stimulation on the outer side of the bilateral upper arms for 20 seconds. To study the influence of somatosensory input on the otolith-ocular reflex, we used sinusoidal off-vertical axis rotation at a tilt angle of 30 degrees. Subjects were rotated with their eyes open in complete darkness at frequencies of 0.32 Hz with a maximum angular velocity of 60 o/s. Results showed a significant gain decrement in EVAR after somatosensory adaptive stimulation, whereas gain change was not significantly different in OVAR. We suggest that somatosensory input had an additive effect on the otolith-ocular reflex in this study. This result could be applied to vestibular rehabilitation using somatosensory input.