Functional relevance of cross-modal plasticity in blind humans

Abstract

Functional imaging studies of people who were blind from an early age have revealed that their primary visual cortex can be activated by Braille reading and other tactile discrimination tasks1. Other studies have also shown that visual cortical areas can be activated by somatosensory input in blind subjects but not those with sight2,3,4,5,6,7. The significance of this cross-modal plasticity is unclear, however, as it is not known whether the visual cortex can process somatosensory information in a functionally relevant way. To address this issue, we used transcranial magnetic stimulation to disrupt the function of different cortical areas in people who were blind from an early age as they identified Braille or embossed Roman letters. Transient stimulation of the occipital (visual) cortex induced errors in both tasks and distorted the tactile perceptions of blind subjects. In contrast, occipital stimulation had no effect on tactile performance in normal-sighted subjects, whereas similar stimulation is known to disrupt their visual performance. We conclude that blindness from an early age can cause the visual cortex to be recruited to a role in somatosensory processing. We propose that this cross-modal plasticity may account in part for the superior tactile perceptual abilities of blind subjects.

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Figure 1: a, Schematic representation of the top of the head showing the scalp positions stimulated.
Figure 2: Error rates (mean ± se.) for stimulation of different positions in the four groups studied.

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Acknowledgements

We thank our subjects for their cooperation; G. Dold and N. Dang for engineering support; E. Corthout, Ulf Ziemann, J. Classen and J. Grafman for comments; and B. J. Hessie for editing.

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Correspondence to Leonardo G. Cohen.

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Cohen, L., Celnik, P., Pascual-Leone, A. et al. Functional relevance of cross-modal plasticity in blind humans. Nature 389, 180–183 (1997). https://doi.org/10.1038/38278

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