Hippocampal systems for event encoding and sequencing during ongoing narrative comprehension.

Narrative comprehension requires encoding individual events and sequencing them into coherent structures. This study demonstrates how the hippocampus contributes to these processes during ongoing narrative processing. Participants viewed a temporally scrambled movie and subsequently recounted its inferred original story during functional magnetic resonance imaging (fMRI) scans. Content encoding and event sequencing abilities were assessed by comparing semantic similarity and temporal order between movie annotations and recall. Functional connectivity between the hippocampus and ventromedial prefrontal cortex (vmPFC) predicted sequencing ability during moments when past and present information are integrated, identified through pre-defined narrative structures and data-driven language models. Conversely, hippocampus-posterior medial cortex (PMC) connectivity predicted content encoding abilities following event boundaries. These findings reveal two distinct hippocampus-centered memory systems in narrative processing: the hippocampus-PMC system for event encoding and the hippocampus-vmPFC system for their integration into coherent narratives.