Environmental and Genetic Influences on Infant Cortical Thickness and Surface Area

Genetic and environmental influences on cortical thickness (CT) and surface area (SA) are thought to vary in a complex and dynamic way across the lifespan. It is established that CT and SA are genetically distinct in older children, adolescents, and adults and that heritability estimates vary across cortical regions. At these ages, various environmental factors have also been shown to have unique influences on cortical structure. Very little is known about how genetic and environmental factors determine infant CT and SA. This represents a critical knowledge gap, especially given compelling evidence that neuropsychiatric disorders have their ultimate origin in prenatal and early postnatal development. In this report, we examine the impacts of 17 major demographic and obstetric history variables on inter-individual variation in CT and SA in a unique sample of 805 neonates who received MRI scans of the brain around 2 weeks of age. Additionally, we examine genetic influences on CT and SA variation using a classical twin model in a subset of 376 twin neonates. Our results reveal that birth weight, postnatal age at MRI, gestational age at birth, and sex are significant predictors of SA and postnatal age at MRI, paternal education, and maternal ethnicity are significant predictors of CT. Additionally, we find that total SA is highly heritable and the relationship between total SA and average CT is under significant genetic control during infancy. Together, these results suggest that genetic, obstetric, demographic, and socioeconomic factors are important determinants of cortical development during infancy. Both genetic and environmental influences drive individual differences in neonatal SA while variation in neonatal CT is largely explained by environmental factors such as paternal education and maternal ethnicity. These findings offer novel insight into how genetic and environmental influences shape infant cortical structure during a delicate and highly malleable period of neurodevelopment and fill important gaps in the current understanding of CT and SA.Doctor of Philosoph