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L.B. Merabet, J. Swisher, S. McMains, M. Halko, J.F. Rizzo, III, A. Pascual–Leone, D. Somers; Activation and Deactivation of Visual Cortical Areas During Tactile Processing . Invest. Ophthalmol. Vis. Sci. 2006;47(13):5877.
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Numerous studies have demonstrated that the occipital cortex of sighted as well as visually deprived subjects is implicated in the processing of sensory information other than vision. Tactile processing has been shown to modulate higher order visual and multisensory integration areas, however the involvement of early visual cortical areas remains unclear.
We employed fMRI in normally sighted, briefly blindfolded subjects with well defined visuotopic borders while they explored and rated simple tactile stimuli. Using their index finger, subjects were asked to rate the overall roughness and inter–dot spacing of randomly presented raised–dot tactile patterns.
Comparison of tactile task performance and an active control condition (exploring a smooth surface) revealed significant activation in primary visual cortex (V1) and deactivation in extrastriate cortical regions V2, V3, V3A, and hV4. Greater deactivation was found in higher visual areas, and across all visual cortical areas, dorsal subregions showed reduced activity relative to their ventral counterparts. Strong modulation of parietal and somatosensory areas was also observed.
These results suggest that tactile processing may recruit two distinct occipital networks; one associated with the specific activation of striate cortex, and another with the global deactivation of visual cortex. This demonstration of cross–modal connectivity in the early visual cortex of sighted individuals supports the concept that the recruitment of visual cortex observed in blind subjects represents the expansion of a preexisting multimodal capacity.
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