Discrepancy between the directions of body sway and gaze during simultaneous optokinetic and posterior neck muscle vibration stimulation

Abstract

We previously reported that optokinetic stimulation elicited body sway in the same direction as the stimulus flow when a fixation target was present, but in the opposite direction when there was no such target. On the other hand, posterior neck muscle vibration reportedly elicits body sway in the direction of gaze. Optokinetic stimulation without a fixation target could elicit not only optokinetic eye movement, but also static shift of the gaze direction. Our aim was to determine, in the absence of a fixation target, whether the gaze direction or optokinetic eye movement drives the body-sway response. We applied posterior neck muscle vibration and optokinetic stimulation simultaneously, and compared the body-sway to the gaze direction. The direction of the elicited body sway was opposite to the optokinetic flow, and the amplitude of displacement was greater than the shift in the direction of gaze. The body sway didn't demonstrate a time-dependent reduction during optokinetic stimulation. We conclude that optokinetic eye movement drives a dynamic, accumulative mechanism that induces a postural response, which exceeds the shift in the direction of gaze.