The proposed experiments investigate the functional organization of the primate frontal eye field (FEF) and its role in the execution of voluntary eye movements, principally saccade and smooth pursuit. For both types of movement, the essential steps are to 1. Select one target from multiple possibilities, 2. Process the spatial parameters of that target, and 3. Reckon the movement metrics that will best track the target. Cortical mechanisms underlying each of these processes will be analyzed:
Aim 1 is to analyze FEF involvement in target selection by teaching monkeys to select peripheral targets based on color and studying the activity of target selection, and eye movement execution. Pursuit- related neurons will be studied during selection between peripheral targets moving in different directions; I hypothesize that these neurons will response on the basis of the selected target, being excited when the target moving in their preferred direction is selected. Target location will be critical factor in analogous experiments of saccade-related neurons, which will also be tested for correlates of the rapid target selection engendered by the express saccade paradigm.
Aim 2 is to analyze the types of spatial target parameters derived from sensory inputs by FEF neurons. Saccade to moving targets are accurate despite displacement of the target during the time needed to register its position and beyond FEF will be ascertained by quantitative mapping response fields of saccade-related FEF cells in conjunction with saccade to moving targets. Similarly, smooth pursuits is guided by not only target velocity, but also by smooth and transient image accelerations and by positional target error. The contributions of each of these distinct parameters, as well as orbital eye position and velocity, to the activity of FEF pursuit neurons will be quantified with a methodology used to analyze pursuit-related activity in the cerebellar flocculus.
Aim 3 is to analyze FEF's role in adaptive influences on eye movement metric by conditioning the oculomotor responses to specific target steps and ramps. Saccade direction will be conditioned by instantaneous displacements of target location while the eye is in flight, and pursuit direction by abrupt changes in target motion direction imposed immediately after pursuit initiation. Correlated changes in motor specification underlying this learning.
Aim 4 is to map the entire FEF representations for saccadic and smooth pursuit eye movements while carrying out the previous 3 aims, and to also explore the arcuate region of frontal lobe cortex for possible representations of vergence eye movements and eyelid blinks. Overall, the proposed experiments will help define the role of the cerebral cortex in effecting different types of eye movements, and thereby contribute to diagnosis and treatment of oculomotor disturbances in neurological disease, and even psychiatric disorders such as schizophrenia.
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