Latent dentate gyrus engrams formed in infancy scaffold adult learning

Infantile amnesia refers to the loss of event-based memories acquired early in life. In mice, however, these memories are not erased; selective optogenetic stimulation of engrams formed in infancy leads to memory recovery in adulthood, indicating that infant-formed engrams can persist in a latent form. We therefore asked whether these latent engrams, although not accessible through natural retrieval, nonetheless influence related adult learning. Using a contextual fear conditioning paradigm, we find that adult learning is facilitated by prior experience in infancy, both for the same and related contexts. Activity-dependent engram tagging revealed that adult learning reactivates infant-acquired dentate gyrus ensembles, and selective inactivation of these ensembles during adulthood abolished this facilitation. These findings indicate that memories formed in infancy persist as latent engrams that scaffold subsequent learning, consistent with a role in establishing schema-like representations.