The long-term goal of the proposed research is the increased understanding of the neural control of eye movement. The major aim during the requested grant period will be the clarification of the role of the posterior parietal association cortex in oculomotor control, and the elucidation of the functional relationship between one sub-area of the interior parietal lobule (IPL) (area POa) and the intermediate and deep layers of the superior colliculus (SC), one of the major premotor regions in the brainstem oculomotor system. This relationship is of special interest because several lines of evidence indicate that the IPL may be involved in the initiation and control of eye movements concerned with the maintenance of gaze upon a visual target. Certain classes of neurons in the IPL become active before and during visually-evoked saccades and visual tracking, while other classes are active during the fixation of interesting targets; electrical stimulation of the IPL evokes eye movements, while lesions disrupt eye movements. Three approaches will be used. In the first, the functional properties of neurons in POa which project to the SC will be determined. Antidromic activation via stimulating electrodes in the SC will be used to discover whether a given neuron is a parietotectal projection neuron. The correlation of the neuron's activity and the monkey's performance on a variety of oculomotor tasks will define the cell's functional category. These experiments will provide important information about the nature of the neural information being transmitted from a key cortical area concerned with eye movements to a major preoculomotor region. These techniques will also be applied to the parietopontine pathway later in the grant period. The second approach is the continuation of ongoing neuroanatomical studies of the connectivity of the IPL with subcortical structures related to eye movement, particularly the SC, the pulvinar nuclear complex, and the lateral pontine nuclei. The third is a behavioral study of the effects of combined frontal eye field and posterior parietal cortex lesions on performance of learned oculomotor tasks in monkeys. The results of these studies will increase our understanding of the basic mechanisms of neural control of behavior, which will in turn aid the understanding of congenital and acquired disorders of nervous system function. In addition, these studies will eventually provide improved tools for diagnosis and for the evaluation of nervous system function in patients following stroke or trauma, and also in the many progressive conditions which are known to affect oculomotor control.
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