Infantile engram modulates memory formation during adulthood

Infantile amnesia refers to the inability to recall early-life experiences, despite their lasting influence on adult behavior. Recent evidence suggests that memory traces formed during infancy may persist in a silent engram state. However, whether and how these silent engram cells contribute to adult memory formation remains unclear. To address this, we examined whether experiences during infancy affect adult memory formation using contextual fear conditioning in mice. Consistent with previous studies, we observed infantile amnesia 30 days later. Despite amnesia, these mice exhibited memory enhancement upon retraining as adults, suggesting that silent infantile engrams influence adult memory. Notably, this effect was context-specific. Using a cellular tagging system and ablation approaches, we found that infantile engram cells in the infralimbic cortex (IL) were crucial for this memory enhancement. Overall, these findings demonstrate that infant engram cells in the IL are re-recruited into adult memory traces, providing a neural mechanism by which early-life experiences shape adult memory formation through relearning.