Figure 1. Including more population representative cohorts of individuals leads to novel insights regarding how the brain ages.

(A) Individuals’ volume of white matter hyperintensities in the brain (WMH; measured at age 45 years) plotted in relation to a measure of their multiorgan physical aging (pace of aging, measured over multiple occasions from 26 to 45 years; n = 851). Individuals that exhibit more accelerated rates of physical aging exhibit worse white matter health at age 45 years (both indicated by higher values). The study cohort represents a wide range of socioeconomic status and key health indicators for individuals of the same age. Each dot corresponds to one participant. Pace of aging was derived from health indicators related to the functioning of multiple organ systems (lower images). Adapted from [10]. (B) Top: longitudinal changes in resting-state functional brain network organization (system segregation) are plotted as a function of educational attainment among adult individuals (n = 265, baseline age 45–86 years, 154 females). Each line corresponds to an individual’s changes in brain system segregation, estimated longitudinally (two to five occasions and ranging over 1–9 years, depending on the individual). Bottom: simple slope plots of average system segregation change scores for three representative ages. The figure panels demonstrate that there is variability in the magnitude and timing of brain network changes across adulthood. However, a significant portion of this variability can be explained by the absence of a college education, particularly among older adult individuals (~65+ years), whereby individuals lacking a college education exhibit accelerated brain network decline. College education was related to other individual- and community-level social determinants of health (not depicted). System segregation is a measure of the functional specialization of the brain network. Lower brain system segregation is linked with worse cognitive ability and alterations in brain activity, and longitudinal declines in system segregation are prognostic of dementia. Adapted from [11]. The inclusion of participants with wider-ranging levels of physical health trajectories and varying life course exposures (the latter indexed by educational attainment) leads to a more accurate estimation of the distribution of brain aging across the population, and reveals distinct patterns and trajectories of brain aging across individuals. Identifying individuals who age in different and tractable ways is an important step towards identifying the causes and consequences of age-related brain decline.