Hippocampal Ablation in Rats: Effects of Intertrial Interval

Abstract

DEFICITS in recent memory following damage to the hippocampus have been reported in man¹ and in the monkey². In a recent investigation³, we tested the hypothesis that the hippocampus is involved in recent memory functions by using different intertrial intervals in runway acquisition and extinction. The method consisted of administering acquisition and extinction trials to rats under either massed or distributed practice conditions. It was found that the temporal spacing of trials during acquisition was not important but that distributed practice trials served to increase resistance to extinction for hippo-campal-damaged rats. The purpose of the work reported here was to clarify the earlier results by determining whether the extinction phenomenon was due to the spacing of trials during acquisition or during extinction. In this work, each subject received both massed and distributed trials during acquisition so that, by the end of this phase of training, all subjects had equal experience with each of the two intertrial intervals. At that time the subjects were extinguished under either massed or distributed practice conditions.