Schedule of Events | Symposia

Hippocampal repulsion as a function of memory similarity and experience

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

America Romero¹ (america@uoregon.edu), Soroush Mirjalili¹, Dominik Graetz¹, Wanjia Guo¹, Eric Wang¹, Ulrich Mayr¹, Brice A. Kuhl¹; ¹University of Oregon

Recent research indicates that interference between similar memories is minimized via targeted differentiation of activity patterns in the hippocampus—a phenomenon we term ‘hippocampal repulsion’. Repulsion is thought to critically depend on the degree of similarity between memories and the amount of experience with those memories. However, potential interactions between similarity and experience are not well understood. Here, participants (n = 50) learned associations between images of scenes and objects. The scenes were drawn from two categories (beaches and gazebos; 24 scenes each). One category (counterbalanced) received high training; the other received low training. During fMRI scanning, participants repeatedly viewed all scenes. fMRI analyses focused on the hippocampus (CA1, CA3/dentate gyrus) and visual cortical areas. For each pair of images within each category, we computed fMRI pattern similarity (separately for each region of interest) as well as a measure of ‘objective’ stimulus similarity based on VGG-16. We found that, for CA3/dentate gyrus, the relationship between stimulus similarity and fMRI pattern similarity strongly depended on experience. Surprisingly, low training was associated with a negative relationship between stimulus similarity and pattern similarity (consistent with repulsion), whereas a qualitatively opposite pattern was observed for high training. This pattern of results differed sharply from what was observed in CA1 and visual cortical regions. Together, these results reinforce the relevance of stimulus similarity and experience in determining hippocampal repulsion but suggest that repulsion may be most likely to occur during the intermediate stages of learning (before stimuli are over-learned).

Topic Area: LONG-TERM MEMORY: Episodic