Children show adult-like hippocampal pattern similarity for familiar but not novel events

The ability to detect differences among similar events in our lives is a crucial aspect of successful episodic memory performance, which develops across early childhood. The neural substrate of this ability is supported by operations in the medial temporal lobe (MTL). Here, we used representational similarity analysis (RSA) to compare neural pattern similarity in hippocampus, perirhinal cortex, and parahippocampal cortex for 4- to 10-year-old children and adults during naturalistic viewing of clips from the same movie or from different movies. Further, we assessed the role of familiarity with individual movie clips on pattern similarity signals in the MTL. In both age groups, neural pattern similarity in hippocampus was lower for clips drawn from the same movies, suggesting that related content activates processes focused on keeping representations with shared content distinct. However, children showed this only for movies with which they had prior exposures, whereas adults showed the effect regardless of any prior exposures to the movies. These findings suggest that children require repeated exposure to stimuli to show adult-like MTL functioning in distinguishing among similar events.