Does cognitive reserve or brain maintenance explain heterogeneity in episodic memory trajectories in late middle age?

Abstract

AbstractBackgroundAging‐related episodic memory (EM) decline and Alzheimer’s disease (AD)‐related brain changes begin in late middle age around age 60. However, rate and severity of cognitive decline do not consistently correspond to the extent of neuropathological changes, suggesting a high degree of heterogeneity in EM trajectories. We tested if brain maintenance (BM; relative absence of changes in neural resources as a determinant of preserved cognition) and/or cognitive reserve (CR; a property of the brain that allows for sustained cognitive performance in the face of age‐related changes and brain insult or disease) explain individual differences and heterogeneity in EM in late middle age.MethodParticipants were 1604 men from the Vietnam Era Twin Study of Aging. A practice effect‐adjusted composite EM score based on six measures was calculated at three time points with mean ages of 56, 62, and 68. Young adult general cognitive ability (GCA) and lifetime years of education were used as proxy measures of CR. BM was assessed as relative change (from age 56 to 68) in cortical thickness and surface area in a bilateral cortical signature of AD regions‐of‐interest (N = 321). We used linear mixed effect modeling.ResultOn average, there was a significant decline in EM from age 56 to 68 (p<0.001). Education (p = 0.042) and young adult GCA (p<0.001) were positively related to EM, but there were no significant effects of education or GCA on the rate of EM change (all p’s≥0.316). Relative brain changes were not related to EM (all p’s≥0.067) and there were no significant interactions of CR proxies and brain changes on EM (all p’s≥0.379).ConclusionHigher education and higher young adult GCA were related to better EM performance across late middle age – with a stronger contribution of GCA compared to education – but EM change did not differ as a function of these proxy CR measures. Our results did not support effects of BM or CR on EM change in late middle age but rather reflected baseline differences in memory in those with low versus high education/cognitive ability. Whether differential change occurs at later ages or with increased AD pathology remains to be determined.