Post-Learning Reactivation of Memories for Naturalistic Continuous Experiences
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Memories are not static records of the past; rather, the act of remembering can change how an event is recalled. Intriguingly, several studies also suggest that memories may be reactivated during rest. However, reactivation has largely been studied for spatial tasks and discrete stimuli, and we know little about whether spontaneous reactivation occurs for long timescale naturalistic events and how reactivation affects retention. Using fMRI, we show that neural activity patterns in the hippocampus and the Default Mode Network during encoding of narrative events were spontaneously reactivated during rest. Contrary to predictions, reactivation did not strengthen recall of movie details, and instead exploratory analyses suggested that reactivation in the hippocampus was associated with more gist-like recall one week later. These findings support the idea that memories for complex events may be spontaneously reactivated, but they suggest that rather than simply strengthening episodic memories, reactivation might help transform them.
Significance statement
We tend to think of memory as a process of recording and later playing back those experiences during retrieval, but some prior evidence suggests the brain may use downtime to process memories to help consolidate them. This paper uses functional MRI to show that the brain activation patterns present while people view films are spontaneously reactivated afterwards during rest. While there was no evidence to suggest that this reactivation strengthened memories, reactivation may be associated with more gist-like memory one week later. These findings suggest that the resting brain processes memories for complex events, but the results call for theories that account for transformations of memories beyond strengthening.
