In normal kittens and cats, cells in a region of primary somatosensory cortex (SI) responded exclusively to input from the contralateral front paw; we called this area paw cortex (PC). A neighboring region of SI responded to input from the contralateral forearm above the wrist; we called this area forearm cortex (FC). The centers of PC and FC were about 4 mm apart. 2. In kittens several weeks after transection of the nerves to the front paw, the following changes were observed in PC: a) 52% of PC cells had receptive fields on the forearm; normally, PC cells responded to natural stimulation only of the front paw; b) many cells in PC (58%) responded to electrical stimulation of the medial cutaneous nerve from the forearm; normally, very few PC cells (9%) responded to this nerve; c) there was a 370% increase in the median amplitude of medial cutaneous-evoked potentials in PC; d) in contrast to these enhanced inputs, PC responses to ulnar nerve stimulation decreased significantly. 3. In adult cats, paw denervation initiated a similar process as in kittens, but with less marked somatotopic changes. 4. In both kittens and adults, FC was unaffected by the nerve injuries. 5. We conclude that a chronic peripheral nerve injury can produce extensive changes in SI cortex somatotopic organization; the nature of the effect is age dependent.
