Ronald J. Tusa - US grants

Multiple visual areas exist in mammalian cerebral cortex. The purpose of this project is to determine, in human beings and trained monkeys, both the immediate and long-term effects upon visual tracking of lesions in specific "visual" areas and pathways. Smooth pursuit with the head still and with the head moving (VOR cancellation), optokinetic nystagmus and saccadic tracking will be examined in monkeys with ablations of: 1) cerebral cortex in one hemisphere, 2) unilateral and bilateral regions of parietal-temporal-occipital cortex, and lesions in the 3) retino-geniculo-striate pathway and 4) retino-tectal-pulvinar pathway. Selected patients who have lesions in these regions will be similarly examined. Eye movements will be measured using the magnetic field search coil technique. "Open loop" performance, a more sensitive measure of pursuit capabilities, will be measured either during the initiation phase of tracking before visual feedback can help, or by using an artificial feedback technique to open the visual feedback loop. The oculomotor behavior of our monkeys and patients will be compared to simulated lesions in models of visual tracking. Monkeys and patients with visual tracking deficits will also be examined for latent and spontaneous nystagmus (ocular motor disorders attributed to visual tracking abnormalities). A more complete understanding of the anatomy and physiology underlying visual tracking will help clinicians to understand better the significance of abnormal visual tracking in patients, as well as a number of human oculomotor disorders which are attributed to visual tracking abnormalities.

To effectively work in our visual environment, we use a spatially- selective attention system to focus attention on stimuli of interest and to ignore surrounding stimuli. The overall objective of this study is to understand better the cortical control of shifts and maintenance of visual attention within extrapersonal space. We will study rhesus monkeys and human patients with cerebral cortical lesions. Maintenance and shifts of attention will be determined by measuring the reaction time to push a button in response to a visual target when attention is engaged at the location of the forthcoming target (maintenance of attention) or at a different location (shifts of attention). We will examine attention deficits for targets located at different spatial sites in monkeys and in patients with unilateral posterior parietal (PP) lesions. This will allow us to determine whether spatial attention in PP cortex in each hemisphere is based on a directional organization for shifts of attention, or on a representational organization where contralateral space is more strongly represented in each hemisphere. If a representational organization is found we will determine whether it is based on a craniotopic (head-centered) or somatotopic (body-centered) coordinate system. Furthermore, by changing the spatial location of the button pushing hand with respect to the head and body, we will determine to what extent PP lesions result in a spatial intentional deficit (preparation to move in response to the stimulus). By examining monkeys with unilateral striate cortical lesions + corpus callosum sections, we hope to determine whether striate cortex or subcortical structures are the major source of visual input into cortex in one hemisphere for use in spatial visual attention. By examining deficits in spatial visual attention in individuals with bilateral PP lesions, we hope to determine the true role of this area in spatial attention without any bias effects of a unilateral lesion. Our results will provide a better understanding of the functional and topographic organization of spatial visual attention mediated by cortex.

This is a Shannon Award providing partial support for research projects that fall short of the assigned institute's funding range but are in the margin of excellence. The Shannon award is intended to provide support to test the feasibility of the approach; develop further tests and refine research techniques; perform secondary analysis of available data sets; or conduct discrete projects that can demonstrate the PI's research capabilities or lend additional weight to an already meritorious application. Further scientific data for the CRISP System are unavailable at this time.