Exploring the Neural and Genetic Substrates of Reading Ability.

Abstract

The primary research goal of this dissertation was to combine multimodal neuroimaging data to investigate the neural and genetic substrates of reading ability. We evaluated structural and functional neural measures for their association with genetic markers and with reading ability. Chapter 2 investigated whether any of reading-related volumetric neural markers were candidate endophenotypes that were associated both with reading ability and with alleles of the KIAA0319 dyslexia-susceptibility gene. We used structural Magnetic Resonance Imaging (MRI) to measure volumetric markers previously associated with reading in 68 adults. The results showed that volume of posterior corpus callosum (pCC) and right inferior frontal gyrus significantly predicted reading performance, and pCC volume was also significantly associated to a risk allele in the KIAA0319 gene. These findings demonstrate that pCC volume is a plausible endophenotype linking the KIAA0319 gene to reading ability. Chapter 3 used diffusion tensor imaging (DTI) to explore the relationship between structural connectivity markers and both reading behavior and genetic risk. The results showed that reduced white matter integrity in the left temporo-parietal region was associated with poor reading performance. Additionally, we found that greater radial diffusivity, which suggests less insulation of myelin sheaths, in the mid-posterior corpus callosum (mpCC) were associated with dyslexia risk alleles of the KIAA0319 gene. We propose that the effect of genetic risk on the volume of mpCC may be related to white matter microstructural changes in the region. Chapter 4 used functional MRI to look for brain regions where neural activation during phonological processing was associated with reading ability. The identified region in the left supramarginal gyrus (SMG) was then used to search for functional connectivity markers. We found that the strength of functional connectivity between bilateral SMG was significantly associated with reading ability, suggesting that this marker is an important neural underpinning of reading. Taken together, our findings extend previous research on the neural and genetic basis of reading and literacy, suggest potential endophenotypes for dyslexia, and point to the importance of efficient connection among a reading-related network. This work helps to advance our understanding of the neural and genetic substrates of reading.