Intracranial self-stimulation after memory reactivation: Immediate and late effects

To assess whether intracranial self-stimulation (SS) given after memory reactivation could improve memory retrieval, we tested the immediate (Experiment 1) and late (24 h; Experiment 2) effects of an SS treatment on the retrieval of a two-way active avoidance conditioning in Wistar rats. Memory was reactivated 24 h after training and the reminder (Rm) used consisted of a 3 s exposure to the conditioned stimulus (a tone) in the same context as in the original learning. SS treatment (2500 trains at 100% of each rat's optimal intensity) was administered immediately afterwards. No significant differences between SS-treated and control groups were observed when the retrieval was tested immediately after the SS treatment with or without memory reactivation. However, retrieval was improved when tested 24 h after SS treatment alone or after the reminder exposure alone. The greatest improvement in avoidance was observed when both treatments were given together, that is, when the SS treatment was administered immediately after memory reactivation. Moreover, there were no significant statistical interactions between the effect of SS treatment and the ones of memory reactivation in any of both experiments. The present results show that the effect of an immediate SS treatment can be added to the ones of memory reactivation causing a strong long-term facilitation of memory retrieval.