INJURY-RELATED AND USE-RELATED PLASTICITY IN THE PRIMARY SENSORY CORTEX OF ADULT MAMMALS - POSSIBLE RELATIONSHIP TO PERCEPTUAL-LEARNING

1. Restricted cochlear lesions in adult animals result in a reorganiza tion of auditory cortex such that the cortical region deprived of its normal input by the lesion is occupied by expanded representations of adjacent cochlear loci (and thus of the frequencies represented at tho se loci), Analogous injury-induced reorganization is seen in somatosen sory, visual and motor cortices of adult animals after restricted peri pheral lesions. 2. Rather than constituting a central compensation for the peripheral loss, such reorganization appears to be an extreme for m of changes in cortical organization that occur as a consequence of a ltered patterns of input such as arise from differential use of restri cted regions of receptor surfaces ('use-related' reorganization). Thus , the frequency organization of auditory cortex is modified in animals trained to perform a frequency discrimination task and analogous chan ges in the frequency selectivity of cortical neurons are produced by c lassical conditioning procedures. 3. Recent evidence from the visual s ystem suggests that changes similar to those involved in injury- and u se-related cortical reorganization may underlie some forms of what has been called 'perceptual learning', the improvement in sensory/ percep tual discriminative performance with practice, Some forms of such lear ning are highly specific to the particular stimuli used in training (i .e. do not generalize to other stimuli), suggesting that the improved performance reflects a change in neural circuitry at a relatively earl y level of sensory processing, The limited available evidence supports the occurrence of such learning in the auditory system. 4. Recent stu dies using functional imaging and related techniques indicate that inj ury- and use-related reorganization occurs in human sensory and motor cortex.