Visual afference mediates head and trunk stability in vestibular hypofunction

Humans must maintain head and trunk stability while walking. The purpose of this study was to compare the kinematics of healthy controls and patients with vestibular hypofunction (VH) when walking and making head rotations of different frequencies in both light and dark conditions. We recruited eight individuals with VH and nine healthy control subjects to perform four tasks at their preferred gait speed, being normal walk, walking and making yaw head rotations at 1.5 Hz and 2 Hz, and walking in the dark and making yaw head rotations at 1.5 Hz. Linear kinematics as well as head, trunk, and pelvis angular velocities were captured using the Vicon motion analysis system (Vicon Motion Systems, Oxford, UK). We found no difference in walking velocities for any of the four walking conditions across groups. The lateral displacement of the center of mass was increased in VH patients. In the dark, patients had more head instability in pitch (larger amplitudes and velocities) even though they were walking and making active yaw head rotations. Patients also had a smaller relative phase angle (mean 3.50 ± standard deviation 2.13°) than controls (mean 10.31 ± standard deviation 2.70°) (p < 0.01). Our data suggest that patients with VH have difficulty walking with a straight trajectory when turning their head. Additionally, patients with VH have an abnormal excursion of spontaneous pitch head rotation while walking and making active yaw head turns, which is dependent on vision. Rehabilitation for these patients should consider applying unique head rotation frequencies when training gait with head turns as well as alternating their exposure to light.