The hippocampus and cortical memory networks have an inflection point in middle childhood

Decades of research on memory development have predominantly shown linear and gradual changes in both the hippocampus and connections between the hippocampus and cortex. However, few studies have investigated the consistency of hippocampal signals across age and how this relates to shifts in connectivity with broader cortical networks that support various memory systems.

In a recent study, researchers analyzed functional magnetic resonance imaging (fMRI) data from children aged 3 to 12 and adults while they watched movies. They evaluated the stability of hippocampal responses using an inter-subject functional correlation (ISFC) approach and measured the functional connectivity between the hippocampus and the Posterior Medial (PM) and Anterior Temporal (AT) cortical memory networks, which are believed to support episodic-like and semantic-like memory, respectively.

The findings revealed that hippocampal responses remain stable in young children, but a notable change occurs around age 7. Half of the children showed their hippocampal responses correlating most strongly with younger age groups, while the other half exhibited stronger correlations with older age groups. Additionally, the study found that while functional connectivity within the AT network remained stable throughout development, connections between the anterior hippocampus and this network did not reach adult levels until around age 7.

This suggests that while the brain networks responsible for semantic memory may be present early on, the interactions with the hippocampus may not develop until after middle childhood. The researchers concluded that there is an inflection point around 7 years of age at which these critical hippocampal-cortical connections begin to mature.