The long term goal of this project is to describe forebrain mechanisms involved in the initiation and visual guidance of eye movements and in the selective fixation of targets. The current objective is to define the supplementary eye field (SEF), a cortical oculomotor area located at the medial edge of the frontal lobe, in terms of its physiological properties, topographical organization, boundaries, and anatomical connections. Electrophysiological experiments (microelectrode recording from single units and microstimulation) will be carried on trained Rhesus monkeys, performing visual-oculomotor tasks. These tasks are designed to reveal the role exerted by the SEF in the voluntary control of fixation, in the generation of internal goals and in the initiation of intended movements. Single unit studies will test specific hypotheses about the properties of various types of cells: visual, fixation, movement and memory cells. Microstimulation experiments will determine the topographical organization of the SEF with respect to saccade characteristics. In particular, they will aim at delimiting territories where eye alone or eye and head (i.e. gaze) are represented. Anatomical experiments will trace the direct connections of the SEF with other oculomotor centers in the cortex, basal ganglia, thalamus and, most importantly, in the SC and the pons. The importance of the SEF in the higher order control of gaze in humans is attested by the effect of frontal dorsomedial lesions which impair the purposive sequencing of saccades, the repression of pure oculomotor reflexes and, more generally, cognition-based eye movements. The importance of the SEF has also been evidenced by PET scans and electrophysiological recordings during the performance of self-generated, voluntary saccades.
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