Differentiation of related events in hippocampus supports memory reinstatement in development

Abstract Memories for similar experiences can be either differentiated or integrated in the adult brain to support later memory retrieval and memory-based decision making. Yet how children represent related memories remains unknown. Here, children (7-10 years) and adults formed memories for separate yet overlapping events. We then measured how successfully remembered events were represented and reinstated using functional magnetic resonance imaging (fMRI). Both children and adults formed differentiated representations in hippocampus—such that related events were stored as less similar than unrelated events. Conversely, only adults formed integrated representations in medial prefrontal cortex (mPFC). Furthermore, hippocampal differentiation among children and mPFC integration among adults tracked neocortical reinstatement of the specific features associated with the individual events. Together, these findings reveal that the same memory behaviors are supported by different underlying representations across development. Specifically, whereas differentiation underlies memory organization and retrieval in childhood, integration exhibits a protracted developmental trajectory.