Reorganization of Visual Cortex in Macular Disease

描述（由申请人提供）：黄斑变性（MD）——由于视网膜损伤导致的中央视力丧失——是发达国家视力损害的主要原因，影响着160多万50岁以上的美国人。中心视力丧失的人必须学会只使用周边视力，因为周边视力的敏锐度和对比度都很低。在正常受试者中，视觉皮层的一大片区域被分配用于处理凝视中心的视觉信息，了解当该皮质区域的输入被MD切断时发生了什么，对于开发更好的视力康复方法至关重要。我们实验室的初步fMRI数据显示了一个惊人的、以前未描述过的现象，在这个现象中，正常受试者对中央凹做出反应的视觉皮层区域在MD受试者中被周围刺激强烈激活，这表明在MD受试者中视网膜定位皮层（FRRC）的功能重组。本提案中概述的研究将使用fMRI扫描MD受试者以及正常对照受试者，当他们看到视觉刺激时，为了测试以下关于MD的假设：1) FRRC在MD发病后迅速发生，并随着时间的推移而增强，因此我们将在每一个中心视野丧失的双眼MD患者中发现FRRC，包括那些最近才发病的患者；2)FRRC即使在单眼MD中也会发生，尽管比双眼MD慢得多；iii)以前的中央凹皮层主要或仅对呈现在“首选视网膜位点”（即MD受试者优先用于阅读和面部识别等任务的幸存视网膜的部分）的刺激作出反应，iv) FRRC仅在暗斑覆盖中央凹时才会被发现，而不是在中央凹不受影响且周边视野受损时，以及v)以前的中央凹皮层有助于MD受试者的视觉表现。但是对于外围（而不是中心）的视觉空间是如此。这项研究的重要性体现在三个方面：1)它将为皮层可塑性及其与行为关系的基础神经科学研究提供信息；2)回答MD患者应对中枢视力丧失的神经机制的基本问题；这将有助于指导MD患者寻找更好的康复策略。

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.