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 la teral 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 l ong duration (3-6 s), low-intensity (0.7 mA) galvanic vestibular stimulatio n (GVS) applied at different times relative to the movement. 2. GVS always produced a tilt of the body in the frontal plane but the resp onse 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 po sture). 3. When the stimulus began 2 s before the voluntary movement the response c onsisted 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 m ovement. The large response observed when GVS onset coincided with the move ment cue resembled the sum (after realignment in time) of these two separat e components. 4. We suggest that these two components of the response to GVS relate to tw o different uses of vestibular information for whole-body control: first, t o 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.