Executive function is known to decline in later life, largely attributed to structural and functional changes in the prefrontal cortex. However, other regions of the brain are integral to executive functioning, including the hippocampus. The hippocampus plays a large role in memory but its intricate connections to limbic regions including the prefrontal cortex likely underlies associations between the hippocampus and executive functions. Due to the hippocampus’ complex structure, hippocampal subregions may be differentially associated with executive function, but this possibility remains largely unexplored. Therefore, we examined the association between volume of the hippocampus and its subregions with executive function to understand these relationships across the adult lifespan.

The study included 32 healthy, community-dwelling participants (age range = 18-81, mean age = 51.06 ± 20.98, 91% white, 72% female) who received a 3-Tesla magnetic resonance imaging (MRI) scan and completed a cognitive battery. We calculated an executive composite based on Trail Making Test Part B and the interference score from the Stroop Color and Word Test. Freesurfer (version 5.3) as used to quantify total hippocampal volume and subfield volumes for CA1, CA2-3, CA4-dentate gyrus, subiculum, and presubiculum. We conducted mixed-effects regression analyses with total hippocampal and subfield volume, age group (young, middle-aged, and older), and their interaction predicting the executive function composite, controlling for total intracranial volume.

Larger hippocampal subregion volumes in CA1 (p = 0.03), the subiculum (p = 0.01), and the CA4-dentate gyrus (p = 0.04) predicted better executive function. Total hippocampal volume and the presubiculum were not significantly associated with the executive function composite. The age group interaction was not significant for any of the models. Follow-up analyses by hemisphere showed that the effects were right lateralized in CA1and CA4-dentate gyrus, and bilateral in the subiculum.

These data support the literature demonstrating the involvement of the hippocampus in executive function and demonstrates variation across hippocampal subfields. The lack of significant age interactions suggests these relationships may not differ across the lifespan, although this finding would need to be replicated in larger samples. These findings support previous literature showing CA4-dentate gyrus’ association with neurogenesis may facilitate better executive function by increasing connection strength among CA1, CA2-3, and the frontal cortex. This study contributes to our understanding of how specific hippocampal subregions relate to executive function, which has both clinical and research implications.