The vestibulo-ocular system serves to maintain gaze stability during head movements. Trauma to the system, or disease states such as gaze palsies or ophthalmoplegia can produce oculomotor deficits that are disorienting and sometimes difficult to resolve clinically. In order to provide more effective treatments for oculomotor and vestibular disturbances, a more thorough scientific understanding of the function of these brain systems must be acquired. Signals from the vestibular labyrinths converge with visual inputs in a region of the brainstem that comprise the vestibular nuclei. Most previous investigations attempting to elucidate the exact role of vestibular nuclei neurons in vestibulo-ocular computations have been limited to examining neural responses that are associated with only horizontal or vertical eye movements. Movement of the eyes and head, however, have three degrees of freedom. In order to understand the sensory-to-motor transformations that control ocular motility, an examination of the neural coding in motor and premotor structures that produces three-dimensional eye movements is necessary. The proposed study will, for the first time, examine the three-dimensional organization of the response properties of vestibular nuclei neurons during spontaneous and visually-evoked eye movements, as well as during head rotation and linear translation. Binocular three-dimensional eye movements will be monitored and correlated with the neuronal discharge. Electrical stimulation will be used to identify vestibular nuclei neurons in terms of their labyrinthine inputs as well as their outputs to abducens, trochlear or oculomotor nuclei. The proposed experiments have two main aims. First to investigate the three-dimensional organization of eye position and eye angular velocity signals in oculomotor related vestibular nuclei cells. Second, to quantitatively evaluate the three-dimensional spatio-temporal organization of head motion signals in these neurons during angular rotation and linear translation. The relationship between the spatial organization of oculomotor and vestibular signals will also be delineated. Electrophysiological studies and theoretical modeling will both be utilized to achieve the specific aims of the proposed project. These results will provide a better understanding of the sensory-to-motor transformations that occur in the vestibulo-ocular system for the control of eye movements that direct vision in a three-dimensional world.
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