Sensory Compensation for Human Vestibular Loss

Fay Horak
Depts of Neurology, Physiology & Pharmacology and Biomedical Engineering, Oregon Health and Science University

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     Last modified: April 28, 2007
     Presentation date: 08/10/2007 9:35 AM in MCC
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Abstract
The effects of vestibular loss on balance function are quite varied across different patients but the reasons for this variation are not well understood. A series of studies in our laboratory has related the effects of vestibular loss on body kinematics and center of mass stability during surface perturbations and gait to their ability to use touch, auditory or vibrotactile biofeedback for sensory substitution. We found that subjects with profound bilateral loss of vestibular function showed increased trunk and head sway, especially while standing on foam or on an inclined surface with eyes closed. Light touch of a finger reduced postural sway similar to use of vision with some patients compensating more than others. The ability to use audiobiofeedback to reduce postural sway in stance depended on each subject's relative dependence on surface or visual information for postural orientation. Specifically, audiobiofeedback reduced sway the most with eyes closed in subjects most dependent upon vision and reduced sway the most when standing on a foam surface in subjects most dependent upon somatosensory information from the surface. Another study of subjects with unilateral loss of vestibular function showed increased trunk instability during lateral surface oscillations consistent with a group average of 50% dependence on vestibular inputs compared to 100% in control subjects. Ability to use vestibular information for postural control, however, varied widely among subjects with unilateral loss and this variation was correlated with their balance confidence and activities of daily living. Specifically, subjects who depended upon their remaining vestibular function, rather than on surface inputs, appeared to have be better compensated. Biofeedback using a vibrotactile vest signaling lateral trunk sway improved postural instability during tandem gait in unilateral vestibular loss subjects. In conclusion, patients with vestibular deficits vary in their ability to use redundant sensory inputs and sensory substitution to improve postural stability with important implications for rehabilitation.