Body response to binaural monopolar galvanic vestibular stimulation in humans

We investigated the possibility of obtaining an anteroposterior body response to galvanic vestibular stimulation (GVS) by applying an equivalent stimulus to both sides of the vestibular apparatus. An original `double fronto-mastoidal' stimulation was used on eight subjects standing with their head facing forwards. Both the onset and the cut-off of the current did induce an anteroposterior body tilt, without any lateral component. The amplitude of the tilt increased as a function of stimulus intensity. GVS evokes anteroposterior or lateral sway of similar spatio-temporal features according to the stimulation configuration. We suggest that the central nervous system makes use of the discrepancy between the left and right vestibular activity to orientate the response: equivalent afferent flows would result in an anteroposterior body response whereas lateral sway is obtained with discrepant ones.