Galvanic vestibular stimulation modulates voluntary movement of the human upper body

1. We have investigated whether vestibular information plays a role in the control of voluntary movement of the upper body. Movement consisted of a lateral tilt of the upper body in the frontal plane through an angle of about 8 deg. The influence of vestibular input was assessed from the effect of long duration (3-6 s), low-intensity (0.7 mA) galvanic vestibular stimulation (GVS) applied at different times relative to the movement. 2. GVS always produced a tilt of the body in the frontal plane but the response was larger and more prolonged when the onset of stimulation coincided with the cue to start moving compared with when it was applied some seconds after movement onset (i.e. while the subject was stationary in a tilted posture). 3. When the stimulus began 2 s before the voluntary movement the response consisted of two distinct components separated in time, one that was linked to the onset of GVS and another that was linked to onset of the voluntary movement. The large response observed when GVS onset coincided with the movement cue resembled the sum (after realignment in time) of these two separate components. 4. We suggest that these two components of the response to GVS relate to two different uses of vestibular information for whole-body control: first, to help maintain balance of the body, and second, to help guide and improve the accuracy of voluntary movements involving motion of the head in space.