Galvanic vestibular stimulation elicits consistent neck motion in seated subjects

Abstract

Galvanic vestibular stimulation (GVS) alters the firing rates of vestibular afferents and consequently provokes the illusion of movement. In standing balance GVS is used to assess the contribution of the vestibular system, where it has been shown to elicit coherent responses in lower extremity muscles involved in maintaining balance. However, to date no information exists regarding the influence of GVS on neck muscles or head-neck stabilization. This study aims to test the hypothesis that GVS can be used as a technique to investigate the vestibular contribution to head and neck stabilization. Sinusoidal stimuli of 0.5 – 2 mA within the bandwidth of 0.4 – 5.2 Hz were used as GVS signals and applied to eleven healthy subjects using a bilateral bipolar configuration. Subjects were blindfolded and stimulated while seated on and restrained to a chair. Measurements of natural sway (without stimulation) were included as control trials. Displacements of head and torso were recorded using a motion capture system. System identification techniques were used to identify the relationship between the input (GVS) and the output (motion) of the head and neck. The results show significant coherence between GVS and the head-neck kinematics and modulation of these responses was observed across frequency and not amplitude, demonstrating the linear range of the vestibular feedback. Furthermore, the vestibular origin of the responses was demonstrated using non-vestibular stimulation tests. EMG measurements were used to characterize the relationship between the vestibular input and muscle activities in neck. Based on the findings of this study we propose that using GVS with system identification techniques provides a viable approach to quantify small motions (~ 0.1 mm) in neck and understand motion control of the head-neck.