The long-range objective of this proposed research is to understand the neuronal mechanisms by which sensory information (both visual and acoustic) is used to direct saccadic eye movements. The research focuses on two major areas: the role of the cerebral cortex in the control of visually-guided eye movements and the interaction of visual and accoustic input onto cells in the deep and intermediate layers of the superior colliculus. The primary methodology consists of single-unit microelectrode recordings made in alert cats that have been trained to execute eye movements towards visual and accoustic targets. Eye movements will be monitored using the scleral seach coil technique, and cats will be trained using feedbck of eye position under computer control. The study of visually-guided eye movements will concentrate on three areas in the visual association cortices: the lateral suprasylvian, middle syprasylvian, and frontal eye fields. These areas all receive visual sensory input, but are hypothesized to be involved in different ways in the processing of this sensory input to motor commands. Differences in the response properties of cells in these three cortical regions to identical experimental conditions will help to elucidate the functional properties of these regions. In addition anatomical tracing studies will compare their efferent connections. Studies of the acoustic and visual interactions will examine cells in the deep layers of the superior colliculus. Since visual input is retinotopically coded and acoustic input is coded in a head-coordinate system, the responses of eye movement cells in the SC to these two inputs will provide useful information regarding the coding of saccadic eye movements. These studies are of interest to neurologists who are treating patients with deficits in eye movement control, and they may also prove useful for diagnosing lesions in the auditory pathway.
