This study will investigate the influence of head-on-trunk position on postural sway in healthy adults using galvanic vestibular stimulation (GVS). During GVS, a small electric current is applied through electrodes placed over the mastoid. The stimulus hyperpolarizes the vestibular nerve on the cathode side and hypopolarizes the vestibular nerve on the anode side. This results in postural sway towards the anode. It is hypothesized that turning the head relative to the trunk will result in a line of sway parallel to a line through the mastoids. Subjects will be asked to stand with their feet together on a force platform. Trials will be conducted with the head forward, and then turned 20,40 and 60 degrees to the right and left with and without the application of sinusoidal GVS. Direction and magnitude of the excursion of center of pressure will be measured using a force platform. The angular and linear movement of the head (forehead), thorax (T4/T5), and pelvis (S2) will be measured using electromagnetic sensors. If a significant difference is found in magnitude and direction of postural sway with different head positions, then the applicability to clinical practice will be investigated. The research protocol will be repeated, as part of a pilot study, with a few patients with a diagnosis of recent whiplash injury with and without complaints of dizziness. If a significant difference is found in the magnitude or direction of postural sway in patients with whiplash injuries as compared with healthy adults then it may prove useful as a diagnostic tool or as an outcome measure to evaluate treatment intervention.
