Educational attainment mitigates hippocampal-related episodic memory decline in individuals at risk of Alzheimer's disease.

Ageing and Alzheimer's disease lead to declines in the brain region underlying memory for past events (hippocampus), and subsequently in memory for past events (episodic memory). However, some people show considerable adaptability in maintaining cognitive processes despite brain ageing or disease. The cognitive reserve model proposes that individual factors (e.g., higher education) may provide cognitive resilience. We measured whether the expected hippocampal-memory association differs according to educational attainment (a proxy of cognitive reserve). At baseline, 62 older adults (65-88 years old) at risk of Alzheimer's disease reported the amount of education completed and received anatomical 3D-T1-w structural MRIs to measure hippocampal volume. They completed a Face-Name Association episodic memory task at baseline, 2 years later, and 4 years later. Educational attainment significantly moderated the effect of hippocampal volume on episodic memory over time, β = -1.97 (SE = .93). Lower hippocampal volume caused greater memory decline at low (mean - 1 SD), but not at moderate (mean) or high (mean + 1 SD) education levels. A Johnson-Neyman analysis revealed that over 14 years of educational attainment is the threshold to eliminate a significant hippocampal-memory effect. The results did not differ by sex. Findings support the cognitive reserve model that individual factors, such as educational attainment, contribute to a cognitive reserve that enables better cognitive performance than would be expected given ageing or disease-related brain changes. Importantly, the findings specify the amount of educational attainment that is protective. Over 14 years of education mitigates hippocampal-related memory decline in people at the risk of Alzheimer's disease.