Influence of the stimulus parameters of galvanic vestibular stimulation on unilateral spatial neglect.

Galvanic vestibular stimulation (GVS) stimulates the vestibular system electrically with low-amplitude direct current through surface electrodes applied to the left and right mastoids. The effects of GVS on unilateral spatial neglect (USN) in poststroke patients were recently reported, but the influence of the current intensity and application duration of GVS on USN has not been sufficiently investigated. Here we explored the influence of these stimulus parameters on USN. We recruited seven patients with right-hemisphere stroke and left-sided USN (four female) for this single-blind, sham-controlled cross-over trial. Their scores on the line cancellation test were measured under three stimulation conditions [left-cathodal/right-anodal GVS (L-GVS), right-cathodal/left-anodal GVS, and sham] at three time points (before the start of GVS, 10 min after the start of GVS, and 20 min after the start of GVS). The GVS intensity was set below the sensory threshold and differed among the patients (0.4-2.0 mA). The cancellation scores were significantly increased after 10 and 20 min L-GVS, with a greater increase observed after the latter (P<0.0001). The other stimulus conditions had no significant effect. There was a significant positive correlation between the change in the increase in the cancellation score with L-GVS and the total charge (r=0.81, P=0.0004). The effect of GVS on USN may depend on its application duration, current intensity, and polarity.