Hippocampal event updating and narrative relation-map updating during naturalistic memory encoding and retrieval

Abstract Naturalistic memory depends on whether an event can be recalled and how accurately its original memory state is reinstated during successful recall. However, how brain-state changes around event transitions and changes in story relationships relate to these aspects of memory remains unclear. Here, we analysed functional magnetic resonance imaging data from 24 participants who viewed and freely recalled 43 naturalistic narrative events, measuring post-boundary hippocampal state changes and changes in narrative relationships. We found that larger late hippocampal state changes predicted successful event recall, with the effect confined to a specific post-boundary window. Among successfully recalled events, larger changes in narrative relationships were associated with more accurate reinstatement of hippocampal states. The relative associations of the two types of change also differed between memory outcomes. These findings suggest that brain-state updating and narrative-relation updating provide complementary perspectives on memory formation and reinstatement under naturalistic conditions.