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Dissociable neural codes for episodic sequence structure across spatial and non-spatial contexts

Poster Session D - Monday, March 9, 2026, 8:00 – 10:00 am PDT, Fairview/Kitsilano Ballroom

Molly Hermiller¹ (), Lila Davachi²; ¹Florida State University, ²Columbia University

Episodic memories unfold as structured sequences that must be bound to, and sometimes protected from, changing context. We developed two matched, naturalistic tasks (City = object-location during navigation; and Soccer = object-person on “team” backgrounds) in which six-step sequences occurred, to test hippocampal-cortical coding of context over time. Participants (N=18, age=18-35) performed interleaved City/Soccer blocks during fMRI. Memory for objects was tested after each sequence; half with changed background. Background memory was later probed end-of-block to assess contextual interference. Trial-wise betas supported representational-similarity measures of context separation among items sharing a background during encoding versus test. Time-resolved models quantified network-engagement dynamics across sequences. Behaviorally, background tests showed higher accuracy for same-context versus changed-context items. On changed-context trials, responses were biased toward the test background, indicating interference. Neurally, context shaped representations: City items sharing a background were decorrelated across sequences (evidence for greater background separation) in parahippocampal/posterior-medial circuitry. Critically, individuals with stronger neural separation within medial-PFC made fewer competitor intrusions, linking representational control to resistance against context-driven confusion. Time-resolved contrasts further dissociated systems: City engaged parahippocampal/posterior-medial cortex throughout the sequence (sustained scene-context scaffolding), whereas Soccer recruited anterior cingulo-parietal control regions early and posterior hippocampus later (early control phase followed by hippocampal pattern completion/detail-rich reinstatement). These results show that context separation and temporally structured network recruitment jointly support sequence learning in naturalistic settings. They suggest a medial-PFC pathway for resisting interference and complementary temporal roles for posterior-medial cortex and hippocampus, beyond simple anterior/posterior or spatial/non-spatial dichotomies.

Topic Area: LONG-TERM MEMORY: Episodic