Health literacy, but not memory, is associated with hippocampal connectivity in adults with low levels of formal education

Introduction: The influence of hippocampal connectivity on memory performance is well established in individuals with high educational attainment. However, the role of hippocampal connectivity in illiterate populations remains poorly understood.

Methods: Thirty-five illiterate adults were administered a literacy assessment (Test of Functional Health Literacy in Adults [TOFHLA]), structural and resting state functional magnetic resonance imaging, and an episodic memory test (Free and Cued Selective Reminding Test). Illiteracy was defined as a TOFHLA score < 53. We evaluated the correlation between hippocampal connectivity at rest and both free recall and literacy scores.

Results: Participants were mostly female (57.1%) and self-declared as being Black individuals (84.8%), with a median age of 50 years. The median TOFHLA literacy score was 28.0 [21.0; 42.5] out of 100 points and the median free recall score was 30.0 [26.2; 35] out of 48 points. The median gray matter volume of both the left and right hippocampi was 2.3 [2.1; 2.4] cm³. We observed a significant connectivity between both hippocampi and the precuneus and the ventral medial prefrontal cortex. The right hippocampal connectivity positively correlated with the literacy scores (β = 0.58, P = 0.008). There was no significant association between episodic memory and hippocampal connectivity. Neither memory nor literacy scores correlated with hippocampal gray matter volume.

Discussion: Low literacy levels correlated with hippocampal connectivity in illiterate adults. The lack of association with memory scores might be associated with low brain reserve in this sample.

Highlights: A significant link was found between health literacy and hippocampal connectivity.Enhanced hippocampus- ventromedial prefrontal cortex connectivity suggests potential cognitive reserve improvement.Higher cognitive reserve may protect against hippocampal atrophy and neurodegeneration.Health literacy improvements could help prevent cognitive impairment in illiterate populations.Study highlights importance of considering structural racism in brain connectivity research.