Functional and structural brain imaging studies of developmental dyslexia

Written language is relatively new from an evolutionary standpoint; however, reading has become an essential aspect of success in everyday life. As with other acquired skills, the ability to learn to read is variable amongst the population. Those with dyslexia struggle to acquire normal reading ability despite normal intelligence, access to education, and a motivation to learn. The brain basis of this neurobiological disorder has been studied at length, but questions remain as to the causality of the anatomical differences and how the brain changes with a reading intervention. This dissertation presents three studies addressing these questions. First, using a reading level matched design, reduction in gray matter volume (GMV) was observed in left middle/superior temporal gyrus when comparing dyslexic children to age-matched control children, consistent with prior studies. However, when compared to a group matched on reading level, these differences were no longer observed. Only right precentral gyrus showed differences compared to both control groups, calling into question the idea that left temporoparietal GMV is causal to the reading deficit in dyslexia. In the second study a reading intervention was given to a group of dyslexic children as well as either a developmental (no intervention) or active (math intervention) control. Here, the data showed an increase in activation in left inferior frontal gyrus that was specific to the reading intervention period and not driven by an underlying change in GMV. Also, bilateral activation of supramarginal/angular gyri prior to the intervention predicted the amount of gain in single word reading standard score following the intervention suggesting functional integrity of this region represents a readiness for intervention. The final study used a subset of the subjects in the intervention study to examine changes in GMV following the intervention. The results showed changes bilaterally in the hippocampus, left precuneus, and right cerebellum, areas involved in more general learning and memory and mental imagery (a key component of the intervention). Together these studies provide insight into the dyslexic brain, and how reading experience (via reading ability or intervention) has an effect on both brain function and structure.