Genetic mediation of the associations among motor and perceptual speed andadult cognitive abilities

Quantitative genetic analyses were conducted to determine the genetic media tion of the associations among motor speed, perceptual speed, and cognitive abilities in normal aging. Measures of motor performance, perceptual speed , and cognitive functioning in four domains (crystallized, fluid, spatial, and memory) were available from the Swedish Adoption/Twin Study of Aging. T he sample included 206 twin pairs ranging in age from 44 to 83 years. A Mot or Speed factor was constructed from 17 timed measures of motor performance . Heritability of Motor Speed was .26 in middle-aged twins and .00 in older twins. Results indicated that genetic variance in cognitive functioning in the middle-aged cohort may be defined by working memory, whereas genetic v ariance in the older cohort was defined by perceptual speed. Indications of a nonshared environmental component in the association among motor speed, perceptual speed, and spatial abilities suggest possible frontal lobe invol vement.