The Development of Hippocampal-Cortical Functional Connectivity in Infants and Toddlers.

Infancy is a critical period for the development of the memory system, yet the functional neural changes that occur during this time remain poorly understood. In adults, long-term memory relies on hippocampal-neocortical coupling, which differs along the hippocampal long-axis. In this study, we investigated resting-state hippocampal-neocortical functional connectivity along the long-axis in 212 infants across the first two postnatal years. We found large increases in hippocampal connectivity with canonical adult memory regions across the first 6 months of age, accompanied by early functional differentiation along the hippocampal long-axis. However, anterior and posterior hippocampal connections continued to fine-tune with age with medial temporal and medial parietal memory-related cortical regions, but also with areas associated with social cognition, salience, and attention in adults. These systems are known to strongly modulate memory formation and retrieval in mature brains. These findings trace the early maturation of hippocampal-cortical coupling along the long-axis, which may play an important role in evolving long-term memory capacity with development.