Repeatedly reactivated memories become more resistant to hippocampal damage.

We examined whether repeated reactivations of a context memory would prevent the typical amnesic effects of post-training damage to the hippocampus (HPC). Rats were given a single contextual fear-conditioning session followed by 10 reactivations, involving a brief return to the conditioning context (no shock). Subsequently, the rats received sham or complete lesions of the HPC. When tested for retention, the HPC rats that experienced the reactivations froze significantly more than nonreactivation HPC rats and did not significantly differ from their respective control group. These findings suggest that memory reactivations contribute to long-term memories becoming independent of the HPC.