Intellectual and social enrichement linked to larger hippocampal volume in healthy aging

Introduction. Decreased hippocampal volume in older adults is associated with episodic memory decline and subsequent neurodegenerative diseases. According to the dynamic polygon hypothesis, strategies that increase neurogenesis of the hippocampus are likely to be successsful in delaying the onset of cognitive impairment in ageing. Several modifiable factors can have a positive effect on the size of the hippocampus, one of them being cognitive reserve. However, to date, very few studies reported an impact of cognitive reserve on hippocampal volume in healthy older adults. Therefore, the main objective of our study was to explore whether cognitive reserve is linked to hippocampal volume in healthy aging. We focussed particularly on intellectual and social enrichment during lifespan, because these aspects have been linked to hippocampal volume in clinical populations.
Methods. Twenty-six healthy late middle-aged participants (51-69 y.o.) underwent 3T magnetic resonance imaging. Hippocampal volume was calculated with the Automatic Segmentation of Hippocampal Subfields (ASHS) software, which uses T1-weighted and T2-weighted MRI to obtain optimal segmentation of the hippocampus and its subfields. Raw volumetric scores obtained with ASHS were controlled for age and total intracranial brain volume. Only the main hippocampal regions (CA1, CA2, CA3, dentate gyrus) were included in the analysis. Volunteers also completed a questionnaire quantifying their lifespan engagement in intellectual (i.e. reading, hobbies) and social (i.e., volunteering, social games) enrichment. More specifically, participants had to describe the frequency of each activity they have engaged in from 6 years old to the present day.
Results. Pearson correlation and hierarchical linear regression analyses revealed that higher frequency of intellectual (r = 0.40; p = 0.023) and social (r = 0.44; p = 0.013) enrichment was significantly linked to larger hippocampal volume, even when controlling for age and sex. Education, another proxy of cognitive reserve, had, however, no significant association with hippocampal volume, possibly due to restricted variance in education and small sample size.
Conclusion. These results suggest that in a late middle-aged population, lifespan intellectual and social enrichment is related to larger hippocampal volume. These findings could indicate that lifespan enrichment promotes hippocampal neurogenesis. Future analysis on a larger sample will distinguish the impact of early and later life enrichment on hippocampal volume and will also assess whether this relation can modulate hippocampal-related changes in episodic memory in aging population.