The overall goal of this project is to understand how sensory signals are translated into commands for the control of movements. More specifically, most of the proposed experiments are concerned with the role of the primate superior colliculus, the frontal eye fields, and the pontine reticular formation in the control of orienting movements of the eyes and head. The first set of experiments tests the hypothesis that the superior colliculus and frontal eye fields generate a unitary signal of the desired change in gaze direction rather than separate signals for the control of eye movements or head movements. The effects of reversible activation and inactivation of small regions of the superior colliculus on the accuracy, velocity, and latency of combined eye-head gaze shifts will be examined. Both microstimulation and chronic single unit recording methods will be used to test the hypothesis that cells with movement-related activity through out the rostral-caudal extent of the superior colliculus specifies a change in gaze. the frequency and duration of microstimulation trains will be systematically varied to determine if neurons in the frontal eye fields are also generating commands to move the eyes and head instead of just being involved in saccadic eye movements. The final experiment in this group will study the activity of neurons in the pontine reticular formation during visually guided gaze shifts involving coordinated movements of the eyes and head. This region of the pons receives signals from the superior colliculus and the frontal eye fields and neurons in this area are the source of projections to spinal cord and motoneurons innervating neck muscles as well as to the motoneurons innervating the extraocular muscles. A second set of experiments focuses on the transformation of collicular signals into those required by the motoneuron pools controlling the direction of gaze. The collicular projections to the paramedian pontine reticular formation will be studies. Detailed plots of the movement fields of pontine neurons will be obtained and a potentially powerful new approach will be used to directly examine the influence of collicular inputs upon pontine cells. This involves varying the number and frequency of stimulation pulses applied to the SC while recording the activity of pontine neurons. Other experiments will examine the effects of reversible lesions of the omnipause area and the paramedian pontine reticular formation in behaviorally trained animals to test key assumptions of various models of the saccadic system.
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