Schedule of Events | Symposia

The subiculum represents semantic boundaries for efficient temporal organization of verbal episodic memory

Poster Session C - Sunday, March 30, 2025, 5:00 – 7:00 pm EDT, Back Bay Ballroom/Republic Ballroom

Jung Han Shin¹ (cautiousjh@snu.ac.kr), Sang Ah Lee; ¹Seoul National University

The human brain can efficiently remember a vast number of experiences through hippocampal segmentation of episodic memories at event boundaries. Crossing event boundaries has been reported to enhance within-context memory and perturb across-context memory. However, studies vary widely on what constitutes an event boundary, ranging from perceptual to semantic changes. Given the importance of semantic information in human cognition, we investigated how semantic boundaries impact the segmentation and temporal organization of episodic memory and its cortico-hippocampal neural correlates. 94 participants memorized ten-word sequences, followed by temporal order judgment tasks during fMRI scanning. In no-boundary trials, all words belonged to a single semantic cluster based on Word2Vec embeddings, whereas in boundary trials, the sequence crossed semantic clusters in the middle. Behavioral results showed that semantic boundaries enhanced temporal order memory accuracy, especially for across-boundary judgments. Accurate memory for higher temporal distances was observed only in within-boundary judgments, indicating the role of semantic boundaries in creating event hierarchies. Semantic boundaries elicited increased activation in cortical regions associated with event boundary detection during encoding, but exhibited reduced orbitofrontal engagement during retrieval, indicating more efficient recall. Within the hippocampus, the subiculum exhibited significant changes in representational pattern dynamics at boundary-crossing. Similarly, the subiculum showed higher pattern similarity for across-boundary judgments compared to within-boundary judgments, highlighting its role in contextual information processing. Our findings demonstrate that semantically driven event boundaries enhance temporal order memory by facilitating the hierarchical chunking of episodes, with the subiculum playing a critical role in event boundary and context processing.

Topic Area: LONG-TERM MEMORY: Episodic