Consolidation Promotes the Emergence of Representational Overlap Across Related Memories in the Hippocampus and Medial Prefrontal Cortex

Abstract

Structured knowledge is thought to form through the extraction and representation of regularities across new learning experiences. However, little is known about how novel episodic memories are transformed over time to reflect such regularities. In a multi-day fMRI study, participants encoded trial-unique associations that shared features with other trials. Multi-variate pattern analyses were used to measure neural similarity across overlapping and non-overlapping memories during immediate and one-week retrieval of these associations. We found that neural patterns in the hippocampus and medial prefrontal cortex represented the featural overlap across memories, but only after a week. Furthermore, after a week, the strength of a memory's unique episodic reinstatement during retrieval was inversely related to its representation of overlap, suggesting a trade-off between the integration of related memories and the recovery of episodic details. These findings suggest that time-dependent changes in neural representations support the gradual organization of discrete episodes into structured knowledge.