Increasing representational capacity in the hippocampal-frontoparietal system underlies hierarchical development of temporal memory.

Time is a central dimension of episodic memory which allows us to remember not only what happened and where from past events, but also when those events occurred and how they relate to one another. Adults can form hierarchical knowledge derived from episodic experience that includes precise timing details about individual events and information about temporal patterns that encode regularities across experiences, alongside factual knowledge about time (e.g., the months of the year). Young children's temporal memory is more constrained, lacking both the level of local detail and limited global knowledge relative to adult temporal representation. Despite behavioral evidence for such developmental differences in temporal memory, we lack a unified model that explains how local and global temporal representation abilities emerge, interact, and are organized across development. Here, we propose a three-stage neurocognitive framework for the hierarchical development of temporal memory, resulting from increasing representational capacity across the hippocampal-frontoparietal memory system. Reviewing behavioral and neuroimaging evidence, we propose that: 1) young children's temporal memory is initially local and event-specific due to functional immaturity of hippocampus; 2) older children and adolescents form and reinstate global knowledge of temporal regularities resulting from enhanced interactions between hippocampus and lateral frontoparietal cortex; and 3) adults flexibly deploy hierarchical knowledge of local details and generalities in new environments mediated by hippocampus and medial frontoparietal cortex interactions. This framework thus provides a unified, empirically-grounded model of temporal memory development, supporting increasingly complex temporal representations that enable adaptive behaviors at a variety of temporal resolutions.