ECS-induced retrograde amnesia is not due to increased sensitivity to sources of ordinary forgetting

Abstract

A series of experiments was conducted with rats to determine if the amount of potentially interfering information presented to a rat immediately following training and electroconvulsive shock (ECS) influenced the magnitude of ECS-induced amnesia. Using one-trial passive avoidance, multitrial active avoidance, one-trial active approach, and appetitive delayed alternation tasks, ECS intensity thresholds were established for each task (Experiments 1, 3, 5, and 7, respectively). Then some subjects were exposed to task-irrelevant high environmental stimulation (of low affective value) immediately following ECS of an intensity that was normally just below the amnestic threshold. Simultaneously, other subjects were exposed to sensory isolation immediately following ECS of an intensity that was normally just above the amnestic threshold (Experiments 2,4,6, and 7, respectively). The posttraining environment in the absence of ECS had no effect on passive avoidance, a nonsignificant tendency towards an effect on active avoidance and active approach, and a strong effect on delayed alternation. When the posttraining environment did have an effect, high stimulation impaired retention and sensory isolation enhanced retention. In no case was there evidence that retroactive stimulus interference was more than algebraically additive with respect to ECS-induced amnesia.