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1 Neurology, Harvard Medical School, MA, Massachusetts, United States
2 Psychology, Boston University, Boston, Massachusetts, United States
* To whom correspondence should be addressed. E-mail: lmerabet{at}bidmc.harvard.edu.
The involvement of occipital cortex in sensory processing is not restricted solely to the visual modality. Tactile processing has been shown to modulate higher order visual and multisensory integration areas in sighted as well as visually deprived subjects however, the extent of involvement of early visual cortical areas remains unclear. To investigate this issue, we employed fMRI in normally sighted, briefly blindfolded subjects with well-defined visuotopic borders as they tactually explored and rated raised-dot patterns. Tactile task performance resulted in significant activation in primary visual cortex (V1) and deactivation of extrastriate cortical regions V2, V3, V3A, and hV4, with greater deactivation in dorsal subregions and higher visual areas. These results suggest that tactile processing affects occipital cortex via two distinct pathways: a suppressive top-down pathway descending through the visual cortical hierarchy and an excitatory pathway arising from outside the visual cortical hierarchy that drives area V1 directly.
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