Identifying brain and behavioral predictors of language and reading development in typically developing and at-risk children
Figuccio, Michael Joseph
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Learning to read is essential, yet many children do not receive a diagnosis of developmental dyslexia (DD) until second or third grade. The aim of this dissertation is to identify brain and behavioral predictors of DD so that diagnosis and intervention can begin sooner. Experiment 1 examines infants with familial risk of DD longitudinally. Infants completed non-sedated diffusion-weighted imaging (DWI) between 4- and 18-months of age and cognitive-linguistic assessment at four years. Infants at- risk of DD displayed reduced fractional anisotropy (FA) and increased radial diffusivity (RD) in the left arcuate fasciculus (AF) and reduced FA and axial diffusivity (AD) of the splenium of the corpus callosum (CC) compared to peers without a familial risk. Both the left AF and CC are implicated in reading and reading-related tasks, and atypicalities have been observed in children and adults with DD. RD may reflect myelination and AD is thought to indicate pathway complexity suggesting infants at-risk of DD exhibit reduced myelination of the left AF and reduced pathway complexity of the CC at or shortly after birth. The left AF assessed in infancy predicted four-year-old vocabulary skills while the CC predicted four-year-old print knowledge. Experiment 2 explores the association between white matter microstructure of the left AF and CC and neural activity during phonological processing assessed via functional magnetic resonance imaging (fMRI). Preschoolers with and without a familial risk of DD completed DWI and an fMRI alliteration task where children indicated via button-press whether two words started with the same initial sound. Positive correlations were observed between FA of the left AF and CC and neural activity in the left medial temporal gyrus and the left lingual gyrus, two regions implicated in phonological processing. Experiment 3 examines whether white matter microstructure of the CC assessed in preschool is associated with school-age reading fluency in children with and without a familial risk of DD. Similar to children and adults with DD, preschoolers with a familial risk of DD displayed greater FA and AD of the CC compared to controls. Furthermore, AD of the CC predicted school-age reading fluency.