Executive functioning in early childhood: etiology and developmental significance
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Executive functioning (EF) facilitates a wide range of purposeful actions and plays a significant role in adaptive functioning. Despite considerable variability in EF, little is known about the factors underlying individual differences in EF in early childhood. The aims of the present research were to explore the genetic and environmental influences on individual differences in EF and the factors underlying the relations between EF and developmentally-significant outcomes. The sample comprised 209 4-year-old twin pairs (79 monozygotic, 130 dizygotic). EF was assessed with the NIH Toolbox: Early Childhood Cognitive Battery, a computerized battery of multidimensional measures. Both observers and parents provided ratings of temperament and parents evaluated behavior problems. School readiness was assessed with a standardized test of basic skills. Model-fitting procedures revealed that variability in set-shifting and inhibitory control could be attributed to both genetic (i.e., 36% and 46%, respectively) and nonshared environmental (i.e., 64% and 54%, respectively) influences. A moderate phenotypic association (r=.30) was found between set-shifting and inhibitory control. Multivariate behavioral genetic models revealed that approximately 85% of the genetic effects on inhibitory control covaried with set-shifting. Set-shifting and inhibitory control were associated with observer-rated task orientation (rs= .29 and .26, respectively) and school readiness (rs= .33 and .34, respectively). Both task orientation and school readiness were heritable (h2= 28% and 82%, respectively) and the correlations between both set-shifting and inhibitory control and these outcomes were due to common genetic influences. Parent-rated temperament was not associated with EF, but a related construct, effortful control, was inversely related to hyperactivity and externalizing behavior problems (rs= -.46 and -.41, respectively). Genetic and environmental factors underlie these associations. These findings indicate that both facets of EF share common genetic underpinnings and that these effects also underlie their associations with developmental outcomes. The present study contributes novel information about the etiology of early EF, with implications for cognitive, socio-emotional, and behavioral development, and ultimately, prevention and intervention efforts.