Effects of galvanic vestibular stimulation during human walking

1. To identify vestibular influences on human calking, galvanic vestibular stimulation was applied to normal adult subjects as they walked to a previo usly seen target. A transmastoidal step stimulus commenced as subjects star ted walking. With the eyes shut, the galvanic stimulus caused large turns t owards the side with the anodal current. 2. Ability to perceive the trajectory of gait without visual cues was measu red by guiding blindfolded subjects from one arbitrary point to another, ei ther walking or seated in a wheelchair. On reaching a destination position and removing the blindfold, subjects pointed to indicate the starting posit ion. Subjects made considerable errors in estimating the trajectory, but we re equally accurate whether in the wheelchair or walking. 3. To determine the effects of vestibular stimulation on the perception of trajectory the galvanic stimulus was applied to blindfolded subjects as the y were guided from one point to another in the wheelchair. The vestibular s timulus produced an illusory shift in the trajectory travelled. This shift was towards the side with the cathode, i.e, in the opposite direction to th e turn produced by the stimulus during walking. 4. We conclude that galvanic vestibular stimulation during walking causes s ubjects to turn from their planned trajectory. In part, this altered course may compensate for an altered perception of trajectory produced by the sti mulus. However, altered perception of the vertical or the base of support, or direct vestibulo-fugal influences on the leg muscles could contribute to the changes in gait.