Conditioned extinction of a reflex in the spinal dog.

Abstract

Permanent extinction of a spinal reflex was demonstrated in the spinal dog. In some preps. a reflex response to tail shock is present in one semitendinosus muscle and absent in the other. When electric shock to tail (CS) was combined with shock to hind paw (UCS) on the side exhibiting no reflex to tail shock, a conditioned response (CR) of the muscle was established on that side. As conditioning was continued and the CR became more firmly established, the inherent reflex of the opposite muscle to CS weakened and disappeared. The reflex did not reappear when CS intensity was greatly increased, when extraneous stimuli were applied, nor when extensive rest periods were interpolated in the conditioning process. The latencies of the respective responses of the two muscles to CS and UCS arranged in order from shortest to longest are: (1) UCR of homolateral muscle; (2) CR of homolateral muscle; (3) Reflex of contralateral muscle to CS; (4) Reflex of contra-lateral muscle to UCS. The response system which has a shorter latency probably enjoys a functional superiority in the bilateral interactions which underlie the extinction of a spinal reflex by the conditioning method.