Dyslexia and thalamus volume : an evaluation of the theories of dyslexia

Reading is critical to success in modern society; however, reading is a significant developmental problem for many children, and researchers are seeking ways to identify dyslexia earlier in a child’s development. The purpose of this study was to identify early predictors of dyslexia using behavioral and neuroimaging data. I collected structural MRI and pre-reading behavioral measures from five year old children that were or were not at risk for dyslexia to determine to what extent these measures predict reading ability two years later. I found that pre-reading ability and intelligence scores at age five correlated significantly with composite reading scores two years later, suggesting that these behavioral measures predict later reading ability. I also found that thalamic grey matter volume correlated significantly with reading ability two years later, above and beyond the behavioral measures, suggesting that thalamic size serves as an additional and independent predictor of later reading ability. This thalamic finding may provide an important bridge between two competing theories of dyslexia development, serve to illuminate our understanding of brain development in individuals with dyslexia, and supply an important advance in early identification of dyslexia in children.