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Rapid formation of a memory engram for complex narratives in the posterior parietal cortex

Poster Session F - Tuesday, March 10, 2026, 8:00 – 10:00 am PDT, Fairview/Kitsilano Ballroom

Monika Schönauer¹, Antonia Lenders¹, Katja K. Kleespies¹, Svenja Brodt², Madeleine M. Sumner³, Elizabeth A. McDevitt³, Christopher Baldassano⁴, Uri Hasson³, Kenneth A. Norman³; ¹University of Freiburg, ²MPI Cybernetics Tübingen, ³Princeton University, ⁴Columbia University

The standard model of systems memory consolidation postulates two interacting memory stores: A hippocampal storage that rapidly encodes new information and a neocortical store where enduring representations develop gradually over time. In the present study, we used functional and diffusion-weighted MRI to investigate where and when participants form content-specific cortical memory engrams for complex naturalistic stimulus material. 40 healthy participants repeatedly watched and freely recounted four movie clips that were set either at airports or at restaurants. We were able to decode the narrative setting from functional MRI data recorded in the posterior parietal cortex (PPC) and the hippocampus. Notably, we observed an increase in content discriminability over learning repetitions in the PPC, indicating a gradual strengthening of a stable neocortical mnemonic representation. Diffusion-weighted imaging revealed that a physical memory trace for the complex episodic narratives formed rapidly in the parietal cortex and was maintained for at least 24 hours after learning. Remarkably, we could discriminate the narrative setting of the watched movies based on these microstructural changes in the PPC. Both functional and structural brain changes were related to how many details participants remembered about the narratives. Our findings suggest that the PPC rapidly forms stable content-specific memory traces for complex narratives from the outset of learning fulfilling all criteria of a memory engram: they directly relate to the learned content, cause a change in the underlying neural substrate, predict memory retention at the behavioral level, and can be observed while lying dormant between times of active processing.

Topic Area: LONG-TERM MEMORY: Episodic