Sensory defects caused by lesions of the first (SI) and second (SII) somatosensory areas of the dog.

Dogs were trained to respond to light tactile stimulation of one of two places on either hindlimb and to flashes of light. One stage or sequential, uni- and/or bilateral lesions were then made in SI and/or SII. The lesions encompassed the hindlimb projection areas, and were placed on the basis of electrophysiological mapping made during surgery. Defects attributable to specific somatosensory deficits were observed after lesions involving SII. No such defects were observed after lesions of SI alone. The defects caused by SII lesions were enhanced by previous or simultaneous lesions of SI. The results suggest that SII rather than SI is of primary importance for the recognition of tactile stimuli, but that SI also may be involved in the tactile conditioned reflex, perhaps as a focus for sensory-motor feedback loops.