Effects of Galvanic Vestibular Stimulation on Posture and Center of Gravity Sway

Stroke patients may have an abnormality in vertical perception of posture called Pusher syndrome. The mechanism of this symptom is thought to be that the patient’s subjective postural vertical is biased toward the paralyzed side due to somatosensory hemiplegia. Therefore, rehabilitation by presenting vertical positions with visual feedback is often performed. However, when combined with visual impairment such as unilateral spatial neglect, rehabilitation may not be as effective as it could be. Galvanic vestibular stimulation (GVS), a technique that uses vestibular sensation instead of vision, has been studied, and GVS improves anodal body tilting and postural sway with stimulation. However, the details of the correlation between the magnitude of body tilting and the intensity of stimulation are unknown. It is also not known how the change in vertical perception of the anode direction by stimulation affects the stability of the center of gravity after the stimulation. In this study, we tested the relationship between GVS stimulus intensity and the magnitude of body tilting, as well as the effect of the stimulus on the sway of the human center of gravity. The results showed a logarithmic relationship between the magnitude of body tilting and the transfer charge of the stimulus. In addition, a change in the anodal direction was observed in the center of gravity position before and after stimulation, suggesting that the change in vertical cognition in the anodal direction due to stimulation also affects the center of gravity position.