Smooth pursuit eye movements respond to moving objects in an attempt to generate smooth eve movements that keep the eyes pointed at the moving object. The neural substrate for pursuit is well known. Visual inputs arise in the retina and pass through the lateral geniculate nucleus to the cerebral cortex. They are transmitted into extrastriate visual areas that process moving images, and through the pons and cerebellum to the final brainstem motor pathways of the eye movement system. This proposal seeks to understand how information is processed between the primary visual receiving areas and the cerebellum. It will do so by using a stimulus known as """"""""apparent motion"""""""" to record, simultaneously, reversible deficits in pursuit eye movements and their manifestation in the electrical activity of neurons within the pursuit system. Apparent motion consists of targets that are flashed sequentially at different locations with different temporal separations: apparent speed is spatial separation (delta-x) divided by temporal interval (delta-t). Preliminary findings have shown that the initiation and maintenance of pursuit degrade in a consistent way as the spatial and temporal intervals are increased.
Four specific aims are planned. 1) Behavioral experiments will expand the understanding of the relationship between deficits in pursuit and the parameters of apparent motion by testing targets that appear across a wide range of visual field. 2) Neural recordings in visual area MT will reveal neural correlates of the apparent-motion induced deficits in the initiation of pursuit. 3) Neural recordings in visual area MST will seek neural correlates of the apparent-motion induced deficits in the maintenance of pursuit. 4) Neural recordings in the cerebellum will document the neural correlates of apparent-motion induced pursuit deficits, in an area that is downstream from most of the visuo-motor processing. These experiments will further our understanding of the neural processing in the cortical component of the pursuit system and should help us to understand the functions of two kinds of areas that are commonly involved in neurological disorders: association areas such as MST and the classical motor control pathway from the cortex to the pons through the cerebellum. Interestingly, the deficits in pursuit caused by neurological lesions are nicely reproduced by the auspicious choice of parameters of apparent motion. Thus, this proposal also has the potential to reveal neural bases for common motor neurological deficits.
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