The role of extraocular muscle proprioception in visual processing and neural control of eye and eye/head movements has remained obscure. In recent years, some fundamental structural characteristics of the extraocular muscle sensory apparatus have been elucidated to the extent that the peripheral receptor apparatus, location of first-order sensory neuron somata, and course and central termination sites of primary sensory neurons are well defined. Furthermore, compelling anatomical and physiological evidence for the interaction of eye and neck muscle proprioceptive signals, potentially functioning in the coordination of eye/head movements, has been obtained. As yet, we have only the most primitive notions regarding the functional role mediated by sensory signals arising from the muscles that move the eyes. While the most profound results of sensory denervation, to date, appear to involve the visual sensory system, only recently have we made any progress into understanding how proprioception is utilized by the oculomotor system. The application represents a continuation of our efforts to determine the anatomical substrate for and functional significance of extraocular muscle proprioception. We are now in the position to apply correlated anatomical and physiological techniques to the problem of extraocular muscle proprioception.
The specific aims of studies to be undertaken in the next project period are directed toward: (a) description of the synaptic relationship of first-order extraocular muscle sensory neurons to second-order neurons in the cuneate nucleus, and of the pathways for subsequent distribution of proprioceptive information and (b) characterization of the nature and precision of signals arising from the eye muscle proprioceptive apparatus by recording from single units in the cuneate nucleus of the chronic alert monkey trained to perform eye movement tasks. Taken together, these studies represent a correlated morphophysiological approach toward understanding what has been a relatively neglected component of the oculomotor and visual systems.
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