Project Summary Accurate memory for a specific past event is a cornerstone of human cognition, allowing for the use of past experiences to optimally guide future behaviors. Episodic memory underlies the ability for children make well-considered decisions, interact with others in a socially appropriate and develop the life narrative that gives coherence to their self-concepts over time. Thus, it is imperative that we understand in detail how memory develops in childhood, and how environmental factors may alter the typical developmental trajectories of episodic memory. There has been much work on age-related differences in encoding and retrieval, and a range of variables have been identified that contribute to age-related improvements in memory function, e.g., poor use of encoding strategies. In contrast, how a critical phase of memory processing – memory consolidation – develops in childhood has received little attention. This lack exposes a crucial scientific gap in our understanding of memory development. In this proposal we examine a key mechanism of memory consolidation called “replay” in the rodent literature, post-encoding reactivation, in the human literature, and how it develops in childhood. This phenomenon was first observed in rodents that were trained to navigate a maze while hippocampal place cell activity was recorded. Later, during post-learning sleep, the neuronal firing patterns within hippocampal place cells recapitulated the firing patterns present during the awake learning phase. Replay can also be observed during periods of quiet wakefulness. This fact has been leveraged in the human literature by examining fMRI scans from rest periods that follow periods of learning. Drawing on predictions derived from computational models of memory, we ask whether poorer memory in children is partly accounted for by perturbed post-encoding reactivation mechanisms. To address this question, both children and young adults will undergo an fMRI scan while encoding associations between items and locations, interleaved with rest scans. We predict that factors that compromise the integrity of the hippocampus, or the ability of the hippocampus to rapidly communicate with neocortex, will alter reactivation and memory performance. Besides examining the key factor of age, children from high and low socioeconomic status (SES) backgrounds will be tested. Low SES/high stress environments have been associated with poorer memory and smaller hippocampi. In addition, we will measure structural connectivity between the hippocampus and cortical regions using cutting-edge imaging techniques. Thus we will examine whether age, environmental factors, and individual differences in structural connectivity alter a key mechanism underlying memory consolidation, and how this set of variables affects the behavioral expression of memory.