BurtonJN03 - The Journal of Neuroscience 23(10:4005 4011 4005 Visual Cortex Activity in Early and Late Blind People H Burton Department of Anatomy

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Visual Cortex Activity in Early and Late Blind People H. Burton Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110 Introduction Brain imaging studies describe visual cortex activity in blind peo- ple during nonvisual tasks such as Braille reading, hearing words, or sensory discriminations of tactile or auditory stimuli [for lit- erature citations see Burton et al. (2002a,b) and Sadato et al. (2002)]. Simply stated, loss of vision does not lead to permanent inactivation of visual cortex. These counter-intuitive findings support the notion of altered capabilities for surviving modalities through reorganization of cortical functions. There are two pos- sible mechanisms for modifying activity in various parts of visual cortex of blind people. One is that the changes constitute de novo cross-modal plasticity in response to severe unimodal sensory deprivation. The potential processes responsible for novel effects involve anatomical and physiological changes that have been studied extensively using animal models (Bavelier and Neville, 2002). Alternatively, observed access of surviving modalities to deprived cortex is an expression, albeit exaggerated, of normal physiology that usually is inhibited or hidden when vision is present. This potential mechanism relies on possible changes in the balance of activity within existing cortical and subcortical networks. These mechanisms are not mutually exclusive given different ages for blindness onset and, therefore, differences in developmental sensitive periods in establishing connections. Data from brain imaging is especially potent in revealing the network of active cortex. Interpretation of this evidence poten- tially can reveal which of these mechanisms mostly influences the behavioral adaptations observed in blind people. However, cur- rent descriptions of affected visual cortical regions differ, espe- cially regarding whether changes occur early in the hierarchy of visual brain areas, particularly in primary visual cortex (V1), or arise in higher tier areas, some of which normally receive input from other modalities. Some studies report V1 responses in early blind subjects (individuals who were born blind or totally lost sight before age 6) (Sadato et al., 1996, 1998, 2002); other studies indicate V1 activity mostly in late blind subjects (individuals with sight at birth, who learned to read print, and who lost sight after age 12) (Bu ¨chel et al., 1998a,b; Melzer et al., 2001). We observed activity throughout portions of visual cortex in all blind individ- uals engaged in a Braille reading task, regardless of the age of blindness onset (Burton et al., 2002a). Identification of the pos- sible factors that are responsible for these differing results con- tributes to consideration of possible mechanisms underlying re- organized activity in visual cortex. Before a discussion of these issues, however, the following briefly summarizes the network of visual cortex responses observed in blind people when they per-
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This note was uploaded on 02/11/2011 for the course BIONB 4230 taught by Professor Finlay,b.l. during the Fall '10 term at Cornell University (Engineering School).

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BurtonJN03 - The Journal of Neuroscience 23(10:4005 4011 4005 Visual Cortex Activity in Early and Late Blind People H Burton Department of Anatomy

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