Effect of gaze on postural responses to neck proprioceptive and vestibularstimulation in humans

1.We studied the effect of gaze orientation on postural responses evoked by vibration of neck dorsal muscles or by galvanic stimulation of the vestibu lar system during quiet standing in health humans. Various gaze orientation s were obtained by different combinations of horizontal head-on-feet (-90, -45, 0, 45, 90 deg) and eye-in-orbit (-30, 0, 30 deg) positions. The instan taneous centre of foot pressure was recorded with a force platform. 2. With a symmetrical position of the vibrator relative to the spine, neck muscle vibration elicited a body sway in the direction of the head naso-occ ipital axis when the eyes were aligned with it. The same result was obtaine d both during head rotations and when the head and trunk were rotated toget her. 3. For lateral eye deviations, the direction of the body sway was aligned w ith gaze orientation. The effect of gaze was present both with eyes open an d eyes closed. After long-lasting (1 min) lateral fixation of the target th e effect of gaze decreased significantly 4. Postural responses to galvanic vestibular stimulation tended to occur or thogonal to the head naso-occipital axis (towards the anodal ear) but in ei ght of the 11 subjects the responses were also biased by the direction of g aze. 5. The prominent effect of gaze in reorienting automatic postural reactions indicates that both neck proprioceptive and vestibular stimuli are process ed in the context of visual control of posture. The results point out the i mportance of a viewer-centred frame of reference for processing multisensor y information.