Cross-modal involvement of visual cortex in tactile perception

It is now accepted that visual cortical areas that are specialized for processing particular aspects of vision are also involved in the corresponding tactile tasks. However, the reasons for such cross-modal recruitment of visual cortex remain unclear. Visual imagery may be a partial explanation, as may the idea that both visual and tactile inputs can access multisensory representations. Studies of connectivity between somatosensory and visual regions could aid insight into these issues. Cross-modal plasticity offers another perspective. The blind show greater recruitment of visual cortical areas in various non-visual tasks. This has been most clearly demonstrated in tasks involving language, but may also apply to tactile perception. There has been recent interest in the effects of short-term visual deprivation, which appears to result in considerable changes in visual cortical activity. This suggests that cross-modal plasticity might not require forming new connections, but instead might be grafted onto existing connectivity between modality-specific areas. This chapter reviews work from many groups on visual cortical involvement in tactile perception in both normally sighted and visually deprived humans, and considers their implications.