FUNCTIONAL ORGANIZATION OF PRIMATE FRONTAL EYE FIELDS

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These proposed experiments will continue investigations into the functional organization of the primate frontal eye fields (FEF) and its role in the control of voluntary eye movements. This sensorimotor cortex will be studied at single cell, columnar, and behavioral levels. The experiments analyze the activity of individual cortical neurons in rhesus monkeys performing sets of sensorimotor tests. Recordings are supplemented by tests for eye movements electrically elicited by microstimulation through the recording electrodes. Anatomical, experimental lesion, and metabolic studies complement the physiological investigations. Specific objectives lesion, investigating the FEF's role in smooth pursuit (SP) eye movements. The subregion of FEF where smooth, rather than saccadic, eye movements are elicited will be mapped and neuronal activity there will be analyzed in relation to SP. Connections of the SP zone will be mapped with HRP. The importance of the FEF for SP will be assessed with FEF lesions, including discrete lesions of the SP zone via microinjection of neurotoxins. Another objective concerns the FEF's role in saccadic eye movements to auditory targets. The topography of auditory activity across the FEF will be mapped, and the issue of whether auditory receptive fields in FEF are remapped by changes in gaze will be addressed. The auditory remapping study parallels a more general investigation into which coordinate system, retinotopic or craniotopic, best describes the different types of FEF saccade-related activity. This investigation involves remapping the response fields of FEF neurons from different fixation points, and will be especially directed at FEF sites where electrically elicited eye movements have "goal-directed" trajectories. A set of objectives revolves around anatomical correlates of the physiological types of FEF cells, such as their laminar location and efferent projections. Laminar location will be addressed by making marking deposits at the sites of particular cell types. Antidromic activation via electrodes implanted in the corpus callosum will determine what information the FEF in each cerebral hemisphere sends the other. The functional topography of the FEF will be mapped with the double-label 2-DG technique. The origin of visual activity in FEF will be determined by recording there after experimental lesions of striate cortex and superior colliculus. Finally, the scope of this investigation will be expanded to provide a comparison of the arcuate sulcus FEF with other cortical eye fields of the rhesus monkey, namely the supplemental eye fields in the medial frontal lobe and parietal eye fields. Clinically, these studies will help in diagnosis and treatment of the oculomotor disturbances that often accompany neurological and psychiatric disorders. The results will bear on the role of the cerebral cortex in commanding eye movement, and should help explain why the primate brain has multiple cortical eye fields and what their different purposes and specializations are.