Center of Pressure Periodic Displacement with Alternate Current Unilateral Vestibular Stimulation

Abstract

Various studies describe the postural response and ocular movements produced by transmastoid galvanic vestibular stimulation (GVS). To take advantage of this response in a noninvasive vestibular prosthesis, a unilateral configuration would be a practical design for users. However, the locomotor response to unilateral GVS on physiological functions related to the vestibular system has not been thoroughly described. To determine the postural effects of unilateral GVS, sine, square and triangle waveforms of 0.3, 0.6 and 0.9 Hz were used to transcranially stimulate the vestibular system of 12 healthy subjects (0.4–2.3 mA). Center of pressure (COP) oscillations were recorded with a stabilometric platform. The largest mean COP trajectory length in the mediolateral axis was produced while stimulating with a sine waveform of 0.3 Hz, followed by stimulation with a square waveform of 0.3 Hz. Oscillation of COP followed stimulation frequency in the mediolateral axis when a sine waveform of 0.6 Hz was used. Root means square (RMS) value and the area of an ellipse calculated from COP displacement recordings, decreased with increasing frequency when stimulating with square and sine waveforms. No changes in these variables were observed when using triangle (symmetric) waveforms. Amplitude of spectral analysis increased notoriously for sine wave stimulation of 0.3 Hz. In future studies, a larger range of frequencies with square and sine waveforms, may be used to study postural response in relation to stimulation frequency. Results suggest that it is possible to include low frequency square and sine waveforms with unilateral GVS in a noninvasive vestibular prosthesis.