SEGMENTAL ORGANIZATION OF CORTICAL AFFERENT AREAS IN THE CAT

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Abstract
Cortical representation of spinal dorsal roots C1 through S2 was defined by recording in the first somatic sensory area (S1) potentials evoked by electrical stimulation of each sensory root in cats under pentobarbital and Flaxedil. Responses were obtained in S1 only from stimulation of contralateral dorsal roots, never from ipsilateral roots. No responses were recorded in "precentral" motor area in contrast to earlier finding in Macaca mulatta. Dorsal spinal roots project upon the "postcentral" area in a shifting overlapping manner. Overlap involves many spinal segments, in contrast to the more limited overlap of dermatomes, and is greater for thoracic and upper lumbar segments than for roots innervating apices of the limbs. The extensive overlap may be accounted for by convergence of afferents and by the mixture of cutaneous and muscle afferents in dorsal roots. Overlap is still more marked in S11 and involves afferents from both sides of the body. Latencies were consistently shorter in Sll than in S1.