Using Neuroimaging Methods to Elucidate Mechanisms of Speech Processing and Reading in Healthy and Dyslexic Populations

This project has several objectives: 1) to study brain mechanisms that enable the development and subsequent maintenance of reading and speech processing skills; 2) to determine how these brain mechanisms fail leading to problems in these skills such as dyslexia; and, 3) to monitor the manner in which remediation interventions exert their beneficial effects on behaviour through the alteration of brain mechanisms. This research will use three major brain-imaging technologies: event-related brain potential (ERP) recordings including high-resolution event-related potentials (hrERP), magnetoencephalography (MEG), and functional magnetic resonance imaging (fMRI).

These studies will be done with children as they develop across the years longitudinally and cross-sectionally. Aspects of the research will also be conducted with adults with skilled reading abilities and those who have long-standing reading difficulties. We will also study children and adults as they progress through reading remediation. In addition, because speech processing abilities interact strongly with reading skills, we will be examining the fundamental speech processing mechanisms such as phonological processing, phonological coding of orthographic units, and the effects of word stress/prosody on spoken word identification. Neuroimaging methods offer unique insights into reading and speech comprehension problems in individuals and provide unprecedented levels of functional monitoring during interventions. We have demonstrated that problem readers show distinct brain activity distinguishing them from efficient readers. More recently, we have shown that successful interventions exert their effects not by merely changing behaviour to fit subsequent evaluation methods but rather by “normalizing” the manner in which the brain processes text and speech signals. Again, our approach to these studies will concentrate on phonological and auditory processing functions as our previous work indicates that these functions form the basis of reading. In our initial Network outline we addressed the following issues: 1. What is the developmental course of reading/speech processing (R/SP) brain responses in normal and dyslexic children and how are they related to behavioural measures; 2. Are neural abnormalities seen in adult developmental dyslexics also seen in dyslexic children; 3. Do neural patterns in dyslexia separate into subtypes or individualized patterns; and, 4. Do therapeutic interventions change behavioural and neural abnormalities simultaneously or do neural changes precede behavioural? Our work during the last two years has shown that the answer to Point 2 would appear to be that yes, adults and children with reading problems exhibit very similar neurophysiological processing abnormalities. Also, our work during this same period has demonstrated that remediation interventions change both neural and behavioural signs of inefficient reading and that the brain changes precede the behavioural indicators (Point 4). Thus, while these results need to be replicated and extended, clear progress is being made in understanding the mechanisms of both problem reading and normal reading.