Activation of the primary visual cortex by Braille reading in blind subjects

PRIMARY visual cortex receives visual input from the eyes through the lateral geniculate nuclei, but is not known to receive input from other sensory modalities1. Its level of activity, both at rest and during auditory or tactile tasks, is higher in blind subjects than in normal controls2, suggesting that it can subserve non-visual functions; however, a direct effect of non-visual tasks on activation has not been demonstrated2–4. To determine whether the visual cortex receives input from the somatosensory system5–8, we used positron emission tomography (PET) to measure activation during tactile discrimination tasks in normal subjects and in Braille readers blinded in early life. Blind subjects showed activation of primary and secondary visual cortical areas during tactile tasks, whereas normal controls showed deactiva-tion. A simple tactile stimulus that did not require discrimination produced no activation of visual areas in either group. Thus, in blind subjects, cortical areas normally reserved for vision may be activated by other sensory modalities.