When compared to the advanced level of knowledge about brainstem control of saccadic eye movements, the understanding of how the cerebral cortex controls saccades is in its early stages. The major goal of the proposed research is to study the cortical control of saccades by analyzing the spatio-temporal distribution of presaccadic potentials from averaged electroencephalographic (EEG) recordings in humans. This technique will be employed to test a model for a trichotomy of cortical control of saccades derived from the current state of knowledge. According to the model, the arcuate frontal eye field (FEF) controls voluntary visually- related saccades, the parietal lobe facilitates the performance by the superior colliculus of visually-elicited reflexive saccades by allowing the release and shifting of visual attention, and the medial frontal lobe in conjunction with the basal ganglia govern self-initiated saccades in the absence of visual targets and the suppression of unwanted saccades. The model will be tested by measuring presaccadic potentials under conditions with varying stimuli and varying degrees of voluntary control in normal subjects and patients with diseases affecting saccadic initiation, including Parkinson's and Huntington's diseases. Aside from gaining information about the normal control of saccades, the results should provide a foundation for studying disorders with impaired saccadic control, and further knowledge about motor control mechanisms in general. A secondary goal of the research program is to develop an alternative neurophysiologic test to ocular electromyography with presaccadic potentials. The spike potential (SP), a manifestation of extraocular muscle or ocular motor nerve activity, will be tested in normal subjects and patients with ocular motility disorders to develop its diagnostic and prognostic capabilities.