The influence of head position on postural sway during galvanic vestibular stimulation

The purpose of this study was (1) to determine the relationship between yaw head- on-trunk position and direction of transverse plane body sway in response to sinusoidal galvanic vestibular stimulation in healthy adults, and (2) to determine if the postural response to galvanic stimulation of individuals with symptoms of cervicogenic dizziness is consistently different from the postural responses of individuals without neck or vestibular pathology.; Thirty healthy adults aged 21–65 years having no history of neurological or otologic dysfunction, no history of neck, spine, or lower extremity injury and normal vestibular function testing were included in the control group. The patient population consisted of eight individuals aged 21–65 with a diagnosis of cervicogenic dizziness. Sinusoidal binaural, bipolar, galvanic vestibular stimulation (GVS) was applied over the mastoids with a peak current intensity of 0.5 mA and a frequency of 0.25 Hz. Six trials lasting 30 seconds were completed for each of seven head-on-trunk yaw positions (0, ±15°, ±30°, ±45°): three with GVS and three without GVS. Anterior-posterior (AP) and medial-lateral (ML) head position, and center of pressure (COP) were recorded continuously during each trial. Head and COP AP and ML recordings were bandpass filtered at the stimulus frequency, and the resulting transverse plane scatter plot fit with an ellipse, which provided estimated parameters of major and minor axis length and direction of sway.; Without GVS, no correlation was found between the mean yaw head position and the mean COP sway direction in both control subjects and patients. During GVS, a linear relationship between mean head yaw position and the mean COP sway direction was found in both healthy adults and people with cervicogenic dizziness. The slope of the regression line approached unity with an intercept through the y-axis near zero. Cervical somatosensory information interacts with galvanic vestibular stimulation such that the direction of postural sway is oriented along the interaural axis of the head rather than along the anterior-posterior or medial-lateral axis of the trunk in healthy adults. Subjects with cervicogenic dizziness do not demonstrate altered cervical vestibular interaction during active head position compared to healthy adults.