Schedule of Events | Symposia

Memory overlap modulates hippocampal integration and differentiation differently in adolescents and young adults

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

Merron Woodbury¹ (merron.woodbury@mail.utoronto.ca), Sagana Vijayarajah¹, Margaret L. Schlichting¹; ¹University of Toronto

The mature hippocampus is thought to store both specifics and regularities across related experiences by forming differentiated and integrated representations, respectively. Here, we investigated how the degree of overlap among experiences may bias different hippocampal subregions towards integration or differentiation. Moreover, we asked whether the hippocampus resolves overlap differently during early adolescence, given its prolonged maturation. Adults (N=36) and adolescents (N=35; 12-13 years old) learned object pairs that overlapped with one another to varying degrees (“high” or “low”). We then identified which regions within the hippocampus showed either higher (integration) or lower (differentiation) similarity among overlapping than non-overlapping pairs, and moreover where this differed by degree of overlap and/or development, using a functional magnetic resonance imaging (fMRI) searchlight. We found a region in the hippocampal head where adults integrated high overlap pairs but differentiated those with lower overlap. By contrast, adults differentiated high but not low overlap pairs in the hippocampal body. Adolescents showed neither integration nor differentiation in the head and instead formed integrated representations only for highly overlapping pairs in the body. Our results are consistent with the idea that memory co-activation, manipulated here through overlap, influences how related experiences are represented in the hippocampus. Moreover, the relationship between overlap and representation varies along the hippocampal long axis in adulthood in a manner not yet mature in early adolescence. Together, our results demonstrate that overlapping experiences are stored differently in the adolescent and adult hippocampus.

Topic Area: LONG-TERM MEMORY: Episodic