Hippocampal maturity promotes memory distinctiveness in childhood and adolescence

Significance Children tend to extract schematic knowledge at the expense of learning and recollecting specific events. Our findings allow us to speculate that the heterogeneous development of subregions within the hippocampus—a brain region crucial for laying down novel memories—contributes to this developmental lag in memory. Specifically, we used in vivo high-resolution structural MRI and memory tests in a large sample of children aged 6–14 years and young adults to characterize hippocampal development. We show that hippocampal maturity as expressed in the multivariate pattern of age-related differences in hippocampal subregions is specifically related to the ability to lay down highly specific memories. Adaptive learning systems need to meet two complementary and partially conflicting goals: detecting regularities in the world versus remembering specific events. The hippocampus (HC) keeps a fine balance between computations that extract commonalities of incoming information (i.e., pattern completion) and computations that enable encoding of highly similar events into unique representations (i.e., pattern separation). Histological evidence from young rhesus monkeys suggests that HC development is characterized by the differential development of intrahippocampal subfields and associated networks. However, due to challenges in the in vivo investigation of such developmental organization, the ontogenetic timing of HC subfield maturation remains controversial. Delineating its course is important, as it directly influences the fine balance between pattern separation and pattern completion operations and, thus, developmental changes in learning and memory. Here, we relate in vivo, high-resolution structural magnetic resonance imaging data of HC subfields to behavioral memory performance in children aged 6–14 y and in young adults. We identify a multivariate profile of age-related differences in intrahippocampal structures and show that HC maturity as captured by this pattern is associated with age differences in the differential encoding of unique memory representations.