Enhancing human balance control with galvanic vestibular stimulation.

With galvanic vestibular stimulation (GVS), electrical current is delivered transcutaneously to the vestibular afferents through electrodes placed over the mastoid bones. This serves to modulate the continuous firing levels of the vestibular afferents, and causes a standing subject to lean in different directions depending on the polarity of the current. Our objective in this study was to test the hypothesis that the sway response elicited by GVS can be used to reduce the postural sway resulting from a mechanical perturbation. Nine subjects were tested for their postural responses to both galvanic stimuli and support-surface translations. Transfer-function models were fit to these responses and used to calculate a galvanic stimulus that would act to counteract sway induced by a support-surface translation. The subjects' responses to support-surface translations, without and with the stabilizing galvanic stimulus, were then measured. With the stabilizing galvanic stimulus, all subjects showed significant reductions in both sway amplitude and sway latency. Thus, with GVS, subjects maintained a more erect stance and followed the support-surface displacement more closely. These findings suggest that GVS could possibly form the basis for a vestibular prosthesis by providing a means through which an individual's posture can be systematically controlled.