The vestibular drive for standing balance control is dependent on sensory cues of gravity

Abstract

By monitoring head movement and orientation in space, the vestibular system can evoke appropriate muscle responses in order to maintain standing balance. The present study investigates whether vestibular-evoked muscle responses are dependent on sensory cues of gravity by examining these responses across varying load and gravity conditions. Standing subjects were exposed to a stochastic electrical vestibular stimulus (EVS, ±5 mA, 0-25 Hz) that induced a vestibular error signal, while vertical loading forces or vestibular signals of gravity were independently modified. A backboard structure limited subjects’ whole-body rotation to the sagittal plane which corresponded with the EVS-evoked sway responses in anteroposterior direction, as the subject’s head was rotated in yaw. Vestibular-evoked muscle responses were greatest when sensory cues of gravity matched the expected terrestrial force of gravity, and decreased when these cues were modified. The reduction was largest when both load- and vestibular-related cues of gravity were different from normal. Our results indicate that the vestibular drive for standing balance control is attenuated when sensory cues of gravity are not congruent to normal (i.e. terrestrial) expectations of standing balance and that the degree of attenuation is dependent upon the cumulative incongruency that arises from multiple sensory cues.