Compensatory plasticity and sensory substitution in the cerebral cortex.

Cats deprived visually from birth show few overt impairments in their natural behavior. Therefore, they seem well suited as an animal model for the study of compensatory plasticity after early vision loss. It can be demonstrated that binocularly deprived cats show improved abilities of auditory localization, and at least equal tactile behavior compared to normal controls. Within the anterior ectosylvian cortex of binocularly deprived cats, where different sensory modalities come together, the anterior ectosylvian visual area is completely taken over by auditory and somatosensory inputs. Furthermore, the auditory spatial tuning of single units in this cortical region is sharpened significantly as a result of visual deprivation. Somatosensory compensation for early loss of vision can be demonstrated by a hypertrophy of the facial vibrissae, and a corresponding expansion of their central representation in the somatosensory cortex of binocularly deprived animals. The compensatory changes in the cortex can be explained by a reorganization of sensory representations under the guidance of sensorimotor feedback rather than by instruction through an extraneous 'supervisory' signal. These processes might form the neural basis of sensory substitution in blind humans.