Temporal patterning of electroshock and retrograde amnesia

Treatments such as electroconvulsive shock (ECS) impair later performance of learned responses if presented shortly after learning, but not if delayed for a sufficient time. These gradients are frequently termed retrograde amnesia and interpreted as reflecting a memory consolidation process. The present investigation was concerned with the relationship of the length of the gradient produced by a single ECS to the duration of the memory consolidation process. In the first experiment, rats were trained on a one-trial passive avoidance task and then presented with one of three ECS treatments. The treatments were five ECSs of 0.5 seconds duration spaced either 1 minute apart, 5 seconds apart, or in one continuous 2.5 second duration burst. The five ECSs spaced 1 minute apart were found to impair performance when presented immediately, 1 hour, 24 hours, and 48 hours but not 9 days after passive avoidance training. Five ECSs spaced 5 seconds apart impaired performance when presented immediately or 1 hour but not 24 hours after training. In contrast, the single 2.5 second duration ECS impaired performance when presented immediately but not 1 hour or longer after training. The impairments produced by the five ECSs spaced 1 minute apart at 1 hour and 24 hours were found to be permanent over 11 days. The second experiment examined whether the long gradient produced by five ECSs spaced 1 minute apart was qualitatively different from single ECS gradients. Five ECSs spaced 1 minute apart were presented following passive avoidance training to rats anesthetized with ether or sodium pentobarbital. In both cases, the series of ECSs still impaired performance when presented 1 or 24 hours but not 9 days following passive avoidance training. This finding does not provide support for a distinction between the gradients produced by a single ECS and a series of ECSs. These results were therefore interpreted as showing that the length of the gradient produced by a single ECS in a passive avoidance task is not a good estimate of the duration of time required for memory consolidation. In this passive avoidance task, consolidation appears to continue for a period of at least several days, while the gradient produced by a single ECS was less than 1 hour. In the third experiment, rats were trained on a one - trial appetitive taste and then presented with either five ECSs spaced 1 minute apart, or a single ECS of 0.5 seconds or 2.5 seconds duration. In contrast to the results in the passive avoidance task, the five ECSs paced 1 minute apart did not produce a longer gradient than a single ECS of either 0.5 or 2.5 seconds duration. All three treatments impaired performance when presented 15 seconds but not 1 hour after training. Several possible explanations for the different effects of the series of ECSs in the two tasks are considered, and it is concluded that this difference probably reflects differences between the memory consolidation processes in the two tasks.Arts, Faculty ofPsychology, Department ofGraduat