Evaluation of postural stability on different types of galvanic vestibular stimulation

This paper presents an analysis on effects of GVS (Galvanic Vestibular Stimulation) to mastoid bone on pos tural balance and stability using 3D motion analysis. The experiments were performed by administering to the experimental subjects different types of GVS (sinusoidal and direct current) during standing and walking, after which postural stability was evaluated using the 3D motion analysis system. Postural stability evaluation during standing was performed by measuring the deviation in the COP (Center of Pressure) and COM (Center of Mass) of subjects standing upright on the force plate and was applied currents with a wide range of stimulus strengths and frequencies (stimulus strengths: 0.1, 0.25, 0.5, 0.7, 1, and 2 mA; stimulus frequencies: 1/64, 1/32, 1/16, 1/8, 1/4, 1/2, 1, and 2 Hz) for 15 seconds. Postural stability evaluation during walking was performed by measuring straight walking status after administering GVS at current of 0.5, 1, and 2 mA to the mastoid process located behind the ears. In the results of the GVS experiments, it was empirically proven that the changes in the many sensory organs, including the vestibular organ, were interpreted by the CNS (Central Nervous System) and feed back to the body, which stabilized standing and walking. During standing, the galvanic current provided to the vestibular organ induced the human body to deviate toward the anode, and the deviation in the COP and COM on the force plate increased as the stimulus intensity was increased. During walking, GVS made the walking path of the gait deviate toward the anode, which was proof of the effectiveness of GVS on posture balance. The major contribution of our study was to provide a novel method for quantitative diagnosis of vestibular organs by investigating the sway of the human body during motion using 3D motion analysis techniques, which are differ ent from previous approaches that only considered the standing condition. Furthermore, it provides an effective guideline for the GVS.