Children with dyslexia frequently present with poor phonological processing. However, it is becoming accepted that neurodevelopmental disorders may be best explained by a poly-factorial model which includes other common deficits as well. One such deficit is executive dysfunction. In the 1980s it was recognized that many children with dyslexia have executive dysfunction;however, research into this area largely fell by the wayside when researchers began examining phonological processing more consistently. As a result, much remains unknown about executive dysfunction in dyslexia, especially in terms of how it relates to frontal lobe structure. Dyslexia and ADHD share a high comorbidity, and executive dysfunction is common in children with ADHD. Thus, it is of interest to determine if executive dysfunction and atypical prefrontal structure may be shared contributors between the two disorders. This project will include 100 children, ages 8-12 years: 25 with dyslexia, 25 with ADHD, 25 with comorbid dyslexia/ADHD, and 25 typically developing controls. All subjects will participate in a neuropsychological evaluation of their executive functioning along with a structural MRI scan. Factor analysis will be used to determine latent variables of executive functions. The following frontal regions will be traced: anterior and posterior cingulate, precentral gyrus, orbitofrontal gyrus, mesial frontal cortex, and the superior, middle, and inferior frontal gyri. Using MANCOVA It is hypothesized that children with dyslexia and ADHD will share deficits in fluency, shift, and verbal working memory. ADHD will also have deficits in inhibition and visual working memory. Moreover, it is hypothesized that the right inferior frontal and left orbitofrontal gyri will be smaller in both groups compared to controls. In contrast, the right superior frontal gyrus, mesial frontal cortex, and right anterior cingulate will be smaller in ADHD than dyslexia and controls. When collapsing across prefrontal regions, gray matter will be reduced bilaterally in dyslexia and ADHD, particularly in the right hemisphere. In addition, left prefrontal white matter volume will be reduced in ADHD. This study will benefit children with dyslexia and ADHD by providing knowledge that may aid diagnosis and intervention. For example, by having a better knowledge of the biological correlates of dyslexia and ADHD, a more rapid diagnosis may be possible than is provided by traditional behavioral techniques. Furthermore, earlier diagnosis will allow for earlier placement in intervention, and early intervention is linked with better outcome than treatment started later.
Developmental dyslexia and ADHD are two of the most prevalent childhood disorders. They also have a high rate of co-occurrence. This project will examine executive functioning (various skills/abilities which contribute to goal-directed behavior) and structure of the front aspect of the brain to see if they may be related to both dyslexia and ADHD.
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