Changes in vestibular function through disease, trauma and aging occur frequently and are particularly pronounced with exposure to unusual motion or gravitational environments. Throughout the history of the manned space flight program, the introduction of the body into microgravity has produced vestibular-related disturbances that result in personal discomfort and a loss in crew performance. Since the symptoms subside within several days of microgravity exposure, it suggests that the vestibular system responses can adaptively change to altered sensory conditions. These changes may be similar to the process of vestibular compensation which is observed following unilateral labyrinthine loss or alterations in visual-vestibular interactions. In order to better understand the nature of vestibular adaptation and its effects upon motor function, the processes underlying neural plasticity and adaptation to altered vestibular signals must be established. The proposed project will utilize systems and electrophysiological approaches to relate stimulus parameters to vestibular adaptation through quantification of the adaptive properties of the vestibulo-ocular reflex and, in particular, the otoli1ith-ocular system in response to changes in the gravitoinertial accelerations (i.e., hypergravity) brought about through centrifugation. Three-dimensional eye movements will be recorded and quantified before and after short-term centrifugal motion. In addition, the underlying neural mechanisms that are responsible for the adaptive behavior will be determined by quantifying the gravity-sensitive properties of behaviorally and electrophysiologically identified vestibular nuclei neurons before and after centrifugation. The adaptive changes in otolith-ocular responses and the associated neural elements need to be understood in order to provide a functional framework regarding adaptive changes in otolith function not only in microgravity but also in vestibular compensation.
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