A confounding of conditioned suppression in passive avoidance: ECS effects

In the one-trial passive avoidance paradigm punishment of a highly probable response results in decreased rates and increased latencies of response. Presumably, Sa have learned to avoid the noxious stimulation by not responding. However, decreased response rates may be produced by an alternative procedure-conditioned suppression-where a freezing response conditioned to the situational cues competes with the previously emitted response. Since both conditioned suppression and passive avoidance procedures have identical behavioral consequences, reduced rates of responding after noxious treatment cannot be explained solely in terms of either paradigm. Moreover, electroconvulsive shock (ECS) may have different temporal effects on behavior resulting from conditioned avoidance and conditioned suppression (Chorover & Schiller, 1966). Their results emphasize the point that if inferences are to be drawn concerning the amnestic properties of ECS, the behavioral consequences of the conditioned suppression paradigm must be distinguished from those of one-trial passive avoidance. No such distinction is apparent in the numerous studies which purport to define the time course of memory consolidation (e.g., Heriot & Coleman, 1962; Weissman, 1964). In the experiments by Heriot & Coleman (1962) and Weissman (1964), rats given a single shock contingent upon a bar press showed subsequent reduced bar press rates. Estes (1944) ,however, has shown that rats shocked between rather than for bar presses also showed reduced response rates. Furthermore, rats subsequently exposed to the apparatus but not permitted to bar press showed recovery of bar press rates. These results suggest that shock delivered in the bar pressing situation can produce conditioned suppression as well as passive avoidance. The two studies reported here investigated the possibility that contingent shock delivered in a one-trial passive avoidance paradigm gives rise to substantial elements of conditioned suppression. If such a possibility could be confirmed, it would support the possibility that the long term amnestic effects of ECS could be due to an alleviation of conditioned suppression rather than to an effect on memory consolidation.