LOCOMOTOR RESPONSES TO GALVANIC STIMULATION OF THE VESTIBULAR SYSTEM IN HUMANS

Balance is control through the integration of vestibular, visual and proprioceptive senses; however, the impact of each during walking is not fully understood. The primary aim of this thesis is to understand the impact of vestibular signals in the maintenance of balance during walking. Galvanic vestibular stimulation (GVS) was used to evoke internal perturbations of the human balance system. Subjects were exposed to GVS during gait and basic results were consistent with published literature; GVS increased the mediolateral deviation of whole body movements towards the side of the galvanic anode during gait. Results indicate that head stability is of key importance to the balance system. The head was held relatively level as compared to the thorax or pelvis throughout gait irrespective of the presence of vision or GVS. Though the pelvis experiences significant tilting due to GVS, a counter rotation of the head compensates for this tilt of lower segments to preserve the level reference frame of the head. Vision was found to be of paramount importance during gait. When walking with eyes open, GVS had a minimal effect on the gait trajectory, spatial foot placement parameters, or tilt angle of the head, thorax, and pelvis. Lastly, temporal ordering of the tilt angles of the head, thorax, and pelvis were observed depending on the perturbation according to the stance limb providing preliminary evidence that segmental tilting occurs during gait. Thus, the well published inverted pendulum model is incorrect for balance losses during gait. Future testing of a greater number of subjects with a larger range of ages and physical condition may provide a greater insight to the intricacies of the human vestibular system