Maturation of Hippocampal Subfields in Young Adulthood and Its Relationship With Cognition

The hippocampus is a key brain region for memory and cognitive functions, which consists of distinct subregions with different developmental trajectories throughout adolescence. However, trajectories of hippocampal subfield change in young adulthood remain uncharacterized, as is their potential relationship with cortical brain aging and cognitive ability during this time. We conducted two magnetic resonance imaging (MRI) follow-ups of a prenatal birth cohort in young adulthood and studied the effects of chronological age and cortical brain age on the volume of hippocampal subfields in the early 20s (n = 109; 51% men) and late 20s (n = 251; 53% men) and how these age-related volumetric changes might relate to full-scale IQ (FSIQ). We showed that CA1 and CA4DG subfields continue to grow in the third decade of life and that this growth can be observed both at the level of chronological age as well as estimated cortical brain age at both MRI timepoints. Moreover, in men, a larger size of these age-related subfields was associated with higher FSIQ, and the deviations between cortical brain age and chronological age mediated the relationships between right CA1 and FSIQ, as well as right CA4DG and FSIQ. These findings reveal that coordinated patterns of advanced cortical brain aging and hippocampal maturation may confer a cognitive advantage in young adulthood.