Post-training intracranial self-stimulation facilitates a hippocampus-dependent task

Previous research has shown that post-training intracranial self-stimulation facilitates implicit or procedural memory. To know whether it can also facilitate explicit memory, post-training intracranial self-stimulation was given to Wistar rats immediately after every daily session of a delayed spatial alternation task that seems to depend on the integrity of the hippocampal memory system. We tested the effects of intracranial self-stimulation in three consecutive learning phases which tried to make the task progressively more difficult: 10 s delay (D 10 phase), 30 s delay (D30 phase), and inverting the starting position of the animals to make their response more dependent on allocentric cues (INV phase). Every phase finished when each rat achieved a fixed learning criterion. Intracranial self-stimulation facilitated the flexible expression of the learned response (INV phase). That is, when the starting position was randomly inverted, only the rats that received intracranial self-stimulation maintained the performance level acquired in the previous training phases. Changing the starting position reduced the correct performance of the non-treated subjects, which need more training sessions to achieve the learning criterion and made less correct responses than treated rats. These findings show that post-training intracranial self-stimulation can facilitate hippocampus-dependent memories. (c) 2004 Elsevier B.V. All rights reserved.