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

Abstract

Summary Structured knowledge is thought to form, in part, through the extraction and representation of regularities across overlapping experiences. However, little is known about how consolidation processes may transform novel episodic memories 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 recovery of episodic details. These findings suggest that consolidation-related changes in neural representations support the gradual organization of discrete episodes into structured knowledge.

Transcending time in the brain: How event memories are constructed from experience

“…These data align with a large body of research focusing on how context or task representations are learned, stored, and used in future tasks. What has emerged from this research is that mPFC represents overlapping prior experiences (Tompary et al, ), or “schemas”, which can also provide scaffolding for integrating and learning new information (Gilboa & Marlatte, ; Preston & Eichenbaum, ; Tse et al, , ; van Kesteren, Rijpkema, Ruiter, Morris, & Fernández, ).…”

“…(b) Results showed that participants were more likely to remember items from the same context as appearing closer together in the sequence; in contrast, participants were more likely to remember items that had spanned a context shift as having appeared farther apart in the sequence. (c) Ratings of closer temporal proximity were associated with greater hippocampal pattern similarity across event boundaries (adapted from "Similarity breeds proximity: Pattern similarity within and across contexts is related to later mnemonic judgments of temporal proximity" by Ezzyat and Davachi, 2014, Neuron, 81(5), p. 1179-1189 [Color figure can be viewed at wileyonlinelibrary.com] (Tompary et al, 2017), or "schemas", which can also provide scaffolding for integrating and learning new information (Gilboa & Marlatte, 2017;Preston & Eichenbaum, 2013;Tse et al, 2007Tse et al, , 2011van Kesteren, Rijpkema, Ruiter, Morris, & Fernández, 2014).…”

Event conjunction: How the hippocampus integrates episodic memories across event boundaries

“…How two memories become integrated, however, is still open to debate. Some theories propose that integration occurs during the encoding of the second memory (i.e., integrative encoding; Nadel, Hupbach, Gomez, & Newman‐Smith, ; Sekeres, Winocur, & Moscovitch, ), while others propose that integration occurs during consolidation or retrieval (i.e., offline integration; Polyn, Norman, & Kahana, ; Tompary & Davachi, ). These processes are not mutually exclusive however, meaning memory integration could theoretically occur both during encoding and during offline periods (Zeithamova & Preston, ).…”

“…Any knowledge of link between A and C would suggest that the distinct memory traces AB and BC have become integrated. Evidence suggests humans are remarkably adept at such inferential tasks (e.g., Backus, Schoffelen, Szebényi, Hanslmayr, & Doeller, 2016;Schlichting, Zeithamova, & Preston, 2014;Tompary & Davachi, 2017;Zeithamova, Dominick, & Preston, 2012). How two memories become integrated, however, is still open to debate.…”

How to see a memory

“…In a 2017 study with Alexa Tompary, then a graduate student in her lab, Davachi showed volunteers pictures of 128 objects, each paired with one of four scenes -a beach scene appeared with a mug, for example, and then a keyboard; a cityscape was paired with an umbrella, and so on. Each object appeared with only one scene, but many different objects appeared with the same scene 11 . At first, when the volunteers matched the objects to their corresponding scenes, each object elicited a different brain-activation pattern.…”