Post-encoding reactivation promotes one-shot learning of episodes in humans

Much work in rodents and in humans has provided evidence that post-encoding reinstatement plays an important role in stabilizing memory beyond initial learning processes. However, it remains unclear whether memory reinstatement is important for the rapid - ‘one-shot’ - learning of an unfolding episode. Here, we asked whether the reinstatement of an episode may occur preferentially post-encoding, when an individual perceives a meaningful event to be concluded. We asked human participants (male and female) to encode sequences of pictures depicting unique episodic-like events. We used representational similarity analysis of scalp electroencephalography recordings during encoding and found evidence for memory reactivation of the just encoded sequence of elements at the offset of the episode. Importantly, memory reinstatement was not observed between successive elements within an episode, indicating memory reactivation was specifically induced once participants perceived the unfolding episode to be completed. We also found that memory reinstatement predicted memory recollection of an encoded episode and that offset memory reinstatement was not present when participants encoded sequences of pictures that were not perceived as meaningful episodes. These results indicate that memory reinstatement at episode offsets is a mechanism selectively engaged to support rapid memory formation of single events.