Speed of time-compressed forward replay flexibly changes in human episodic memory

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Abstract

Remembering information from continuous past episodes is a complex task1. On the one hand, we must be able to recall events in a highly accurate way, often including exact timings. On the other hand, we can ignore irrelevant details and skip to events of interest. Here, we track continuous episodes consisting of different subevents as they are recalled from memory. In behavioural and magnetoencephalography data, we show that memory replay is temporally compressed and proceeds in a forward direction. Neural replay is characterized by the reinstatement of temporal patterns from encoding2,3. These fragments of activity reappear on a compressed timescale. Herein, the replay of subevents takes longer than the transition from one subevent to another. This identifies episodic memory replay as a dynamic process in which participants replay fragments of fine-grained temporal patterns and are able to skip flexibly across subevents.

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Fig. 1: Experimental design and behavioural results.
Fig. 2: Reinstatement of oscillatory patterns from encoding.
Fig. 3: Chronometry of memory replay.
Fig. 4: Illustration of several replay speeds and their aggregation.

Data availability

Group statistical data relating to this project are deposited in a public repository (https://doi.org/10.25500/eData.bham.00000254). The individual data that support the findings of this study are available from the corresponding author upon request.

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Acknowledgements

The authors thank the SPMIC—specifically G. O’Neill, B. A. E. Hunt and L. Gascoyne—for help with data collection. This work was supported by the ERC Grant Code4Memory (647954) awarded to S.H., who is further supported by the Wolfson Society and Royal Society. B.P.S. is supported by a Sir Henry Dale Fellowship jointly funded by the Wellcome Trust and the Royal Society (107672/Z/15/Z). The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.

Author information

S.M., B.P.S. and S.H. conceived and designed the experiments. S.M. performed the experiments. S.M. analysed the data under the supervision of S.H. S.M., S.H. and H.B. contributed reagents, materials and analysis tools. S.M. and S.H. wrote the paper, with comments and edits by B.P.S. and H.B.

Correspondence to Simon Hanslmayr.

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Supplementary Notes, Supplementary Methods, Supplementary Figures 1–7

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