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Episodic memory retrieval is supported by rapid replay of episode content

Our everyday experience shapes how we represent the structure of the world. Retrieval of these experiences from memory is fundamental for informing our future decisions. To uncover the fine-grained neurophysiological mechanisms that support such retrieval we studied participants who first experienced unique multi-component episodes, and subsequently completed cued memory retrieval of these whilst undergoing magnetoencephalography (MEG). Successful retrieval was supported by sequential replay of episodes, with a temporal compression factor greater than 60. This sequential replay was stronger in those participants with weaker overall memories. Replay direction, forward or backward, was dependent on whether a participant’s goal was to retrieve elements of an episode that followed, or preceded, a retrieval cue. Our results demonstrate that memory-based decisions are supported by a rapid replay mechanism that flexibly shifts in direction.