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Delaying exception introduction enhances children’s hippocampal engagement during category learning

Poster Session C - Sunday, March 8, 2026, 5:00 – 7:00 pm PDT, Fairview/Kitsilano Ballroom

Sagana Vijayarajah¹, Michael L. Mack, Margaret L. Schlichting; ¹University of Toronto

Grouping items based on regularities (“categorization”) also entails reconciling items that do not fit these regularities (“exceptions”), an ability that improves over development. Computational models have linked hippocampal subfields to different roles during categorization in the mature brain: Cornu ammonis 1 (CA1) may be sensitive to regularities, whereas CA2,3/dentate gyrus (DG) may be sensitive to exceptions, especially when encountered after learning category regularities. Although category learning improves throughout childhood, little is known about how brain function supports this learning over development. Children (7–9 years) performed two learning phases that trained them to group items into categories with feedback, the only difference between phases being when exceptions were introduced—either at the start (“early”) or after exposure to category regularities (“late”). Each phase ended with a test on the category membership of the items. Behaviourally, children’s exception learning did not vary by exception timing. We next characterized whether subfield engagement during each task varied by when exceptions were introduced. There were no differences in CA1 versus CA2,3/DG engagement, potentially reflecting a lack of subfield specialization in children during categorization. Instead, engagement of both subfields varied by task and exception timing, with greater activation during learning when exceptions were introduced late versus early, and the reverse at test. These results suggest that, despite no behavioural differences in exception learning, delaying exception introduction preferentially engages children’s hippocampal mechanisms. More broadly, particular instructional sequences may enhance children’s engagement of hippocampal learning mechanisms, with future work needed to characterize the behavioural significance of this difference.

Topic Area: LONG-TERM MEMORY: Development & aging