Biological mechanisms underlying the unity and diversity of executive functions in childhood
Executive functions (EFs) are supervisory cognitive processes that coordinate the execution of other cognitive operations necessary for learning and everyday functioning. In spite of a growing literature associating EFs with health-relevant outcomes across the lifespan, relatively little is known about the sources of individual differences in these processes during childhood and adolescence. Our research team and others have begun to investigate EF within a multidimensional structure, whereby individual differences in EFs are attributable to variance specific to individual tasks, variance common to tasks via domain-specific factors, and variance shared across domains via a general EF factor. This dissertation presents three papers that explore the biological sources of the EF structure in a population-based sample of 7- to 15-year-olds from the Texas Twin Project. Given the role of EF in models of complex reasoning and intelligence, Paper 1 uses a twin approach to estimate the extent to which genetic contributions to EF overlap with genetic influences on intelligence. I find that a general EF factor representing variance common to inhibition, switching, working memory, and updating domains accounts for substantial proportions of variance in intelligence, primarily via genetic pathways. In Paper 2, I turn to cortisol, an established biomarker of stress reactivity, as a second biological mechanism that explains individual differences in EF in childhood. We investigate associations between EF performance and neuroendocrine output via cortisol measured over three distinct time scales. We find that general EF most strongly correlates with cortisol trajectories surrounding an acute stressor and that the association is due to entirely shared genetic influences. Paper 3 assesses the extent to which children’s and adolescents’ neural activity converges across EF domains and whether these patterns are consistent with adult EF-related activity. Using functional magnetic resonance imaging to examine brain activity shared across EF tasks in a large pediatric sample, we find that brain regions that are consistently engaged across switching, updating, and inhibition tasks closely correspond to the cingulo-opercular and fronto-parietal networks identified in adult studies. The integration of behavioral genetic, neuroimaging, and endocrine methodologies enable us to test specific neurobiological mechanisms by which genetic and environmental processes affect EFs.