Processing speed and longitudinal trajectories of change for cognitive abilities: The Swedish Adoption/Twin Study of Aging

In this manuscript, The Swedish Adoption/Twin Study of Aging (SATSA) is described. Although the study is a multidisciplinary program in gerontological genetics, the summary of findings focuses on the cognitive measures. In the second part of the manuscript, we investigate the role played by measures of processing speed in explaining the longitudinal trajectories of change for cognitive abilities and the genetic and environmental influences on those trajectories. When processing speed was regressed out of cognitive measures representing three cognitive domains (crystallized, fluid, and memory) and a general cognitive factor, the trajectory of decline was less severe. Quantitative genetic analyses indicated that environmental variance increases in late adulthood. A substantial portion of the genetic variance for these cognitive abilities was accounted for by genetic variance for speed. With increasing age, genetic variance associated with processing speed becomes a more prominent component of genetic variance for fluid abilities and for the general cognitive factor.