Abstract

Sensory substitution refers to the capacity of the brain to replace the functions of a lost sense by another sensory modality. This cross-modal plasticity has been documented both in animals and humans deprived of a particular sensory modality, such as vision or audition. Discovering new ways to exploit this cross-modal plasticity may help to optimize the recovery of sensory loss. The most commonly used form of sensory substitution is Braille reading, which enables the blind to read by using the somatosensory system. Recently, a human–machine interface, the tongue display unit (TDU), which uses the tongue as a medium for visual substitution in blind subjects, has been developed. We trained six congenitally blind and five blindfolded, sighted controls to use the TDU to perform a visual orientation discrimination task. Subjects were positron emission tomography (PET) scanned before and after an intensive 1-week training program with the TDU. Before training, no increased activity was measured in the visual cortex of either group during the orientation detection task. However, after training, patterned stimulation of the tongue activated the visual cortex in congenitally blind subjects. Sighted controls did not show occipital activation post-training despite equivalent performance on the same task. These data reveal the development of cross-modal plasticity in the brains of congenitally blind subjects. They further show that the time course of neuroplasticity in humans can be remarkably rapid.

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