Reorganization of Visual Cortex in Macular Disease

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DESCRIPTION (provided by applicant): Macular degeneration (MD)-the loss of central vision due to retinal damage-is the leading cause of visual impairment in the developed world, affecting more than 1.6 million Americans over the age of 50. Individuals with loss of central vision must learn to cope with peripheral vision only, which has low acuity and contrast sensitivity. In normal subjects, a large region of visual cortex is allocated to processing visual information at the center of gaze, and an understanding of what happens to this cortical region when its input is cut off by MD will be critical in any effort to develop better methods of vision rehabilitation. Pilot fMRI data from our lab shows a striking and previously undescribed phenomenon in which the region of visual cortex that responds to the fovea in normal subjects is strongly activated by peripheral stimuli in MD subjects, indicating functional reorganization of retinotopic cortex (FRRC) in MD. The research outlined in this proposal will use fMRI scanning of MD subjects as well normal control subjects while they view visual stimuli, in order to test the following hypotheses about MD: i) that FRRC occurs rapidly after the onset of MD and strengthens over time, such that we will find FRRC in every binocular MD subject who has central field loss, including those who have developed the disease very recently, ii) that FRRC occurs even in monocular MD, although more slowly than in binocular MD, iii) that formerly foveal cortex will respond primarily or only to stimuli presented in the "preferred retinal locus" (i.e. that part of the surviving retina that MD subjects use preferentially for tasks such as reading and face recognition), iv) that FRRC will be found only when the scotomas cover the fovea, not when the fovea is spared and the peripheral visual field is compromised, and v) that formerly foveal cortex contributes to visual performance in MD subjects, but does so for peripheral (rather than central) visual space. This research is important for three reasons: 1) It will inform research into the basic neuroscience of cortical plasticity and its relationship to behavior; 2), It will answer fundamental questions about the neural mechanisms by which MD subjects cope with loss of central vision; 3) It will help guide the search for better rehabilitation strategies for people with MD.