Building bridges: the hippocampus constructs narrative memories across distant events

Abstract

SummaryRecent studies have suggested that activity in the hippocampus is increased during divisions between events in memory, or “event boundaries.” Although hippocampal activity at event boundaries may play a role in segregating adjacent events, it might also serve a counterintuitive purpose: to bridge the divide between distant events that form a larger narrative. We used functional neuroimaging to investigate whether patterns of hippocampal activity at event boundaries support the integration of distant events in memory, when these events can form a larger narrative. During encoding of fictional stories, boundary-evoked hippocampal activity patterns were more similar between distant events that formed one coherent narrative, than between distant events from unrelated narratives. Twenty-four hours later, detailed recall of coherent narrative events was supported by the reinstatement of boundary-evoked hippocampal activity from encoding. These findings reveal a key function of the hippocampus: the dynamic integration of events into a narrative structure for memory.

Relating the Past with the Present: Information Integration and Segregation during Ongoing Narrative Processing

“…As noted above, one of our key hypotheses is that memory reactivation supports the integration of these reactivated memories with new inputs (for related work, see Cohn-Sheehy et al, 2020;Griffiths & Fuentemilla, 2020;Clewett, DuBrow, & Davachi, 2019;Backus, Schoffelen, Szebényi, Hanslmayr, & Doeller, 2016;Schlichting & Preston, 2015Zeithamova, Dominick, & Preston, 2012;Zeithamova, Schlichting, & Preston, 2012;Zeithamova & Preston, 2010;Shohamy & Wagner, 2008). This integration hypothesis is supported by several aspects of our results.…”

Narratives bridge the divide between distant events in episodic memory

“…These studies have generally not investigated the role of narrative coherence in memory integration. As we report elsewhere (Cohn-Sheehy et al, 2020), our recent neuroimaging work suggests that coherent narrative events might become integrated during memory encoding.…”

“…In closing, our work shows that recall of temporally distant events can be enhanced if events can be integrated into a coherent narrative, which suggests that narratives provide a beneficial organization for events in memory. Ongoing neuroimaging investigations will further reveal the narrative architecture that supports episodic memory (Cohn-Sheehy et al, 2020).…”

A content-based representational scaffold for naturalistic event memories

“…Participants were scanned during free recall of each film, and following the scan session, they completed a recognition memory test consisting of statements about the events. A standardized protocol was used to score recall data (Cohn-Sheehy et al, 2020) for the number of verifiable details with respect to content in the video clips (see Methods for further details). Participants generally recalled many details about each movie, and each participant recalled information from each event.…”

“…Lu et al used a computational modeling approach to find that selectively storing information at event boundaries (but not mid-event) was beneficial to storing and later retrieving that information (Lu et al, 2020). Relatedly, a recent study by Cohn-Sheehy and colleagues suggests that event boundaries may act not only as moments in which an event transition occurs, but moments in which related information can be integrated across distinct experiences (Cohn-Sheehy et al, 2020). Future studies should continue to investigate representational timescales with respect to specific event components.…”