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The organization of part of the primary somatosensory cortex was examined in anesthetized raccoons at 2, 8, or 16 weeks after the normal peripheral input to this region of cortex had been removed by amputation of the fifth digit. Electrophysiological recordings were made in and around the cortical area representing the fifth digit. Eight intact animals were used to verify that this specific area could be accurately localized on the basis of the sulci and to determine the normal response characteristics of this area. The results from nine animals with the fifth digit removed provided evidence for a gradual reorganization of the cortical area which had been functionally denervated. At 2 weeks postamputation the field was almost totally unresponsive to sensory input. At 8 weeks many sites were responsive to high intensity stimulation of rather extensive regions of the hand. At 16 weeks the cells fired more readily to peripheral stimulation than at 8 weeks and tended to have smaller, more restricted receptive fields. The location of receptive fields in this latter group suggested that the fifth digit area was taken over primarily by input from the fourth digit. The time course of this reorganization is suggestive of extensive anatomical changes either within the cortex itself or at subcortical levels.

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1. Multi-unit recordings were made from SI cortex of barbiturte-anesthetized cats. In four cats, multiple vertical penetrations were made at closely spaced intervals. In 12 cats, long surface-parallel penetrations were made in the rostrocaudal or the lateromedial directions with observations taken every 100 micron. 2. Evidence is presented suggesting that cytoarchitectonic area 3a receives input from deep receptors and area 3b receives input from cutaneous receptors. 3. Within area 3b there was an abrupt change in submodality such that the rostral portion of 3b was activated by slowly adapting (SA) afferents, while the caudal portion was activated by rapidly adapting (RA) afferents. 4. The change in modality from deep to cutaneous occurred at the 3a/3b border, but the change in submodality occurred within area 3b and there was no obvious anatomical correlate of the latter transition. 5. These data suggest that there are modality- and submodality-specific bands in register with the bands of cytoarchitecture that extend across the mediolateral dimension of primary somatosensory cortex (SI). 6. A particular receptor population (or populations) from all regions of the body delivers information to each functionally specific band--one map is found in area 3a and two are in area 3b. If this pattern holds for the rest of cat SI, then there must be additional maps of the body in cytoarchitectonic areas 1 and 2.