To evaluate the influence of somatosensory input on the vestibulo-ocular reflex (VOR), we used sinusoidal rotation tests in 19 young, healthy volunteers. For the control condition, subjects were sinusoidally rotated in complete darkness and with eyes opened at a frequency of 0.2 Hz with a maximum angular velocity of 30 degrees /s for 30s, and at frequencies of 0.4 and 0.8 Hz with a maximum angular velocity of 60 degrees /s for 30s. Sinusoidal tests were performed at earth vertical axis rotation (EVAR). For the experimental condition, we introduced somatosensory stimulation as subjects were sinusoidally rotated at the control parameters. Subjects were told to grasp an earth-fixed metallic bar with their right hands. Thus, their right arms continued to move as the rotating chair apparatus moved. We observed a significant increment (34%) in VOR gain change only at 0.2 Hz EVAR when subjects held the bar compared to that of the controls, who did not hold the bar. Gain change did not differ significantly across the other conditions. We hypothesize that arthrokinetic input (i.e., arm movement) had an additive effect on VOR in this study. This input might relate to a low-frequency component that strongly enhances the velocity storage system. Our findings have applications to types of vestibular rehabilitation regimens that implement somatosensory input.
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