FUNCTIONAL ORGANIZATION OF PRIMATE FRONTAL EYE FIELDS

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This research will study the functional organization of the primate Frontal Eye Fields (FEF) at single cell, columnar, and behavioral levels, using physiological, anatomical, metabolic, and behavioral techniques. Recent studies have revealed a spectrum of FEF cell types that respond in conjunction with visually-guided saccadic eye movements. This study will determine which cell types lie in which cortical layers, and how response fields within a 'column' are aligned. Other FEF neurons respond in conjunction with smooth pursuit eye movements; these cells will be analyzed and related to the eye movements elicited by electrical stimulation at the same site. FEF neurons that respond to auditory stimuli will also be studied, and auditory response fields will be analyzed as a function of direction of gaze and perceived sound direction. All recording studies will also examine the callosal connectivity of each characterized single neuron by testing stimulation electrodes implanted in the corpus callosum, thus determining which cell types and response field dimensions are callosally connected. Other experiments concern FEF organization at the level of neighborhoods of cells or cortical columns. Physiological maps, reflecting eye movements elicited with low-level microstimulation, will be imposed on the overall pattern of callosal connectivity by making tracer injections in the contralateral FEF. Another anatomical study will relate saccade organization in the FEF to the retinotopic map in the superior colliculus. A double-label 2-deoxy-D-glucose experiment will portray the overall mapping of eye movements across the FEF by having monkeys will make specific opposing patterns of eye movements for each label. Total FEF ablations and discrete physiologically-defined lesions will bear on the behavioral role of the FEF in different oculomotor behaviors, including reading-like saccade patterns and smooth pursuit. The ultimate source of visual activity in the FEF will be studied by unilateral removal of striate cortex or the superior colliculus. Altogether, these studies should further define the FEF role in programming voluntary eye movements and will also have clinical relevance for the large, heterogeneous population of patients with eye movement disorders.