Age- and reserve-related increases in fronto-parietal and anterior hippocampal activity during episodic encoding predict subsequent memory

Remembering associations between encoded items and their contextual setting is a feature of episodic memory. Although this ability generally deteriorates with age, there is substantial variability in how older individuals perform on episodic memory tasks. This variability may stem from genetic and/or environmental factors related to reserve, allowing some individuals to compensate for age-related decline through differential recruitment of brain regions. In this fMRI study spanning a large adult lifespan sample (N=154), we used multivariate Behaviour Partial Least Squares (B-PLS) analysis to examine how age, retrieval accuracy, and a proxy measure of reserve (i.e., a composite of years of education and premorbid I.Q.), impacted brain activity patterns during spatial and temporal context encoding and retrieval. We also conducted a secondary B-PLS to explore whether higher cognitive ability was associated with additional compensatory patterns capturing other aspects of reserve not accounted for by our composite measure of education and I.Q. Our results showed that higher reserve did not moderate the effect of age on cognitive ability or context memory, but higher cognitive ability was associated with better context memory performance and with task-specific compensatory responses in ventral visual, temporal, and fronto-parietal regions in advanced age. Additionally, higher reserve was associated with task-general responses in superior temporal, occipital, and inferior frontal regions. These findings suggest that task-specific compensatory responses in the aging brain are modulated by differences in general cognitive ability, which may be related to accumulated reserve, but not by proxy measures of reserve based on premorbid I.Q. and years of education.