Posturography following rotation: A model of posture control during vestibular dysfunction

Postural stability is influenced by multiple sensory inputs, including visual, somatosensory, and vestibular cues. Adaptive changes in how these sensory inputs influence posture may occur in the presence of vestibular dysfunction. In this study, we simulated vestibular dysfunction in normal subjects in order to study immediate and adaptive modifications in postural control under reproducible and reversible experimental conditions. Twenty subjects (ages 20 to 35 years) were tested on a force-detecting platform; the support surface or visual surround was modulated (anterior-posterior) proportionally to body sway. Vestibular dysfunction was simulated by rotating subjects with their eyes closed at 180 degrees/second for 30 seconds, then rapidly halting rotation. Posturographic measures were obtained during the subsequent 20 seconds. Ten identical rotation trials for each subject were performed, alternating the direction of rotation, and with either the support surface or the visual surround modulated with sway in different subjects. Thus, only one sensory modality could provide Earth-stable sensory cues. Control groups were tested to assess effects of repeated alternating rotations alone, and effects of repeated posturographic trials alone. Sway was quantified by measuring peak-to-peak excursions of the center of mass. Results showed that subjects were more stable after rotation when they were provided with a stable support surface than with a stable visual surround. No subject could maintain stance without at least one Earth-stable sensory input. Improvement of mean sway scores in either group was not significant, although isolated cases did exhibit adaptive changes with improved stability over repeated trials. Control studies suggested that effects of repeated rotations or posturographic trials alone were insignificant. We conclude that rotary vestibular stimulation provides a useful model of vestibular dysfunction for the study of multisensory influences on postural control and adaptive processes that help stabilize stance.