Daily dynamics of resting-state EEG theta and gamma fluctuations are associated with cognitive performance in healthy aging

Healthy age-related cognitive changes are highly heterogeneous across individuals. This variability is increasingly explained through the lens of spontaneous fluctuations of brain activity, now considered as powerful index of age-related changes. However, brain activity is a biological process modulated by circadian rhythms, and how these fluctuations evolve throughout the day is under investigated. Assessing the daily dynamics of brain fluctuations involves the use of techniques measuring the temporal dynamics of synchronized communications between brain regions, such as electroencephalography. We found that theta and gamma daily fluctuations in the salience-control executive inter-network (SN-CEN) are associated with distinct mechanisms underlying cognitive heterogeneity in aging. Higher levels of SN-CEN theta daily fluctuations appear to be deleterious for memory performance and were associated with higher tau/neuroinflammation rates. In contrast, higher levels of gamma daily fluctuations are positively associated with executive performance, and were associated with lower rate of {beta}-amyloid deposition. Thus, accounting for daily EEG fluctuations of brain activity contributes to better understand subtle brain changes underlying individuals cognitive performance in healthy aging.