Source memory improves substantially during childhood. This improvement is thought to be closely related to hippocampal maturation. As previous studies have mainly used cross-sectional designs to assess relations between source memory and hippocampal function, it remains unknown whether changes in the brain precede improvements in memory or vice versa. To address this gap, the current study used an accelerated longitudinal design (n = 200, 100 males) to follow 4- and 6-year-old human children for 3 years. We traced developmental changes in source memory and intrinsic hippocampal functional connectivity and assessed differences between the 4- and 6-year-old cohorts in the predictive relations between source memory changes and intrinsic hippocampal functional connectivity in the absence of a demanding task. Consistent with previous studies, there were age-related increases in source memory and intrinsic functional connectivity between the hippocampus and cortical regions known to be involved during memory encoding. Novel findings showed that changes in memory ability early in life predicted later connectivity between the hippocampus and cortical regions and that intrinsic hippocampal functional connectivity predicted later changes in source memory. These findings suggest that behavioral experience and brain development are interactive, bidirectional processes, such that experience shapes future changes in the brain and the brain shapes future changes in behavior. Results also suggest that both timing and location matter, as the observed effects depended on both children's age and the specific brain ROIs. Together, these findings add critical insight into the interactive relations between cognitive processes and their underlying neurologic bases during development.

SIGNIFICANCE STATEMENT Cross-sectional studies have shown that the ability to remember the contextual details of previous experiences (i.e., source memory) is related to hippocampal development in childhood. It is unknown whether hippocampal functional changes precede improvements in memory or vice versa. By using an accelerated longitudinal design, we found that early source memory changes predicted later intrinsic hippocampal functional connectivity and that this connectivity predicted later source memory changes. These findings suggest that behavioral experience and brain development are interactive, bidirectional processes, such that experience shapes future changes in the brain and the brain shapes future behavioral changes. Moreover, these interactions varied as a function of children's age and brain region, highlighting the importance of a developmental perspective when investigating brain-behavior interactions.

童年时期的源记忆显着改善。这种改善被认为与海马体的成熟密切相关。由于之前的研究主要使用横断面设计来评估源记忆与海马功能之间的关系，因此尚不清楚大脑的变化是否先于记忆的改善，反之亦然。为了解决这一差距，当前的研究采用了加速纵向设计（ n = 200，其中 100 名男性）对 4 岁和 6 岁的人类儿童进行了为期 3 年的跟踪。我们追踪了源记忆和内在海马功能连接的发育变化，并评估了 4 岁和 6 岁群体在没有艰巨任务的情况下源记忆变化和内在海马功能连接之间的预测关系的差异。与之前的研究一致，源记忆和已知参与记忆编码过程的海马和皮质区域之间的内在功能连接与年龄相关。新的发现表明，生命早期记忆能力的变化预示着海马体和皮质区域之间的后期连接，而内在的海马体功能连接则预示着源记忆的后期变化。这些发现表明，行为体验和大脑发育是互动的、双向的过程，因此体验塑造了大脑未来的变化，大脑也塑造了未来行为的变化。结果还表明，时间和地点都很重要，因为观察到的效果取决于儿童的年龄和特定的大脑投资回报率。 总之，这些发现为认知过程及其在发育过程中的潜在神经基础之间的相互作用关系提供了重要的见解。

意义陈述横断面研究表明，记住先前经历的背景细节（即源记忆）的能力与童年时期海马体的发育有关。目前尚不清楚海马功能的变化是否先于记忆的改善，反之亦然。通过使用加速纵向设计，我们发现早期源记忆的变化预测了后来的内在海马功能连接，并且这种连接预测了后来的源记忆变化。这些发现表明，行为体验和大脑发育是互动的、双向的过程，因此体验塑造了大脑未来的变化，而大脑也塑造了未来行为的变化。此外，这些相互作用随着儿童年龄和大脑区域的变化而变化，凸显了在研究大脑行为相互作用时发展视角的重要性。