The development of a systematic approach to the diagnosis and management of ataxias of vestibular origin depends critically on the elucidation of the complex sensory and motor interactions involved in human postural control. In this paper, the results of studies of both sensory and motor control of posture in adults and children with peripheral vestibular deficits are summarized and reviewed. In studies of the sensory organization of postural control, normal subjects and patients with peripheral vestibular deficits were exposed to unreliable information from their support surface and/or visual surround during quiet stance. While normal adults and children were able to maintain balance under these conditions, the majority of children and adults with peripheral vestibular deficits showed one or both of the following abnormalities: (1)Vestibular loss patients were unable to maintain equilibrium when forced to rely on vestibular information for postural control. (2)Vestibular distortion patients were unable to select an accurate source of sensory information when exposed to sensory conflicts during quiet stance. Preliminary results of studies of motor coordination in these patients also suggest that vestibular loss patients rely almost exclusively on ankle sway to control posture, even during balance tasks which require hip movements to maintain equilibrium. In contrast, some vestibular distortion patients appear to rely on hip motions, even when not required to do so to maintain balance. The results of these studies are discussed in terms of the implications for both sensory and motor aspects of postural control in patients with ataxias of vestibular origin.
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