Cross-modal reorganization of human cortical functions.

Recent technological development has opened fascinating opportunities in research on cognitive functions of the human brain. For example, cortical representations of sensory functions and their reorganization, which have been studied thoroughly in animals, are far better understood in humans now than they were only a decade ago. Hemodynamic and electromagnetic studies have demonstrated that a modality-specific brain area that is totally deprived of its normal sensory input becomes responsive to stimulation of other modalities. The functional significance of this cross-modal activation was recently indicated by, for example, studies showing that the occipital cortex of the blind is activated by sound changes, when the task is to detect these changes. Moreover, trans-cranial magnetic stimulation applied to the occipital cortex of blind individuals results in distortions and omissions of letters in Braille text being read by the subject. Contrary to prevailing views, cross-modal neural reorganization might, as shown by recent results, take place even in the mature human brain.