Dyslexia: Longitudinal study of brain dysfunctions

Since the advent of functional magnetic resonance imaging (fMRI), numerous studies found that the brains of dyslexic readers exhibit activation patterns which differ from those of nonimpaired readers in two posterior regions of the left hemisphere. In skilled readers, these regions form a highly organized cortical system for reading. Despite the success in mapping of brain dysfunction in dyslexic readers, little is known about their emergence and/or development during reading acquisition. As reading is an evolutionary recent cultural invention, infants do not possess any neuronal structures with an inherent specialization for printed words. Rather, it is assumed that our ability to read emerges from changes in brain systems initially specialized for other cognitive functions - e.g. visual object perception and language processing - which meet the requirements for reading. The present project will conduct an early starting longitudinal study, tracking nonimpaired and dyslexic childrens brain function and structure during reading acquisition. The project captures two innovative aspects of current MRI based dyslexia research. It will be (i) one of the first comprehensive MRI-based dyslexia studies which allow to identify brain characteristics which precede difficulties in learning to read, and (ii) among the first longitudinal MRI-based studies which provide information on how the brains of normally progressing children adapt to the requirements of learning to read, and how the brains of dyslexic children deviate from the normal adaptation. The present project is planned for a three years-perdiod. A Kindergarten-Screening will identify children at-risk and not-at-risk for later becoming dyslexic. We will acquire brain data from these children at the end of Kindergarten, at the end of Grade 1 and at the end of Grade 2. Assessments of reading progress at the end of Grade 1 will identify these children who actually developed the disorder. Brain data collection at the end of Grade 1 and Grade 2 will only include at-risk children who exhibit serious reading difficulties. To reduce drop out rate and to obtain high quality MRI data from our young children, special efforts will be made to make children feel at ease during the MRI sessions. We will acquire a comprehensive set of brain data, including task based fMRI data, structural MRI data of gray matter and white matter tracts, and fMRI data during rest. Results from our project may help to clarify the question, which brain abnormalities reflect the neural correlates of developmental dyslexia at a particular stage of reading development, and which abnormalities actually reflect the primary dysfunctions that hinder these children at learning to read.

This project provides results enhancing our understanding of structural and functional brain changes during literacy acquisition in young children. In a longitudinal study functional and structural MRI data was collected from children shortly before learning to read (end of kindergarten) and after reading acquisition. We could show that a region in the left inferior frontal cortex exhibited increased activation during implicit word processing during the early stage of literacy acquisition from the end of kindergarten to the end of first grade. This increase in activation was accompanied by a decrease in gray matter volume in the same region and an increasing left lateralization of activation during early literacy acquisition. These brain changes were positively associated with the reading ability of children at the end of Grade 1. Additionally, during this time period learning to read was associated with an increased functional connectivity between left inferior temporal and inferior frontal regions during processing of visual words, but also during rest in the absence of a task. Furthermore such changes were not found in a control group of children of nearly the same age that remained in kindergarten for one more year. This pattern shows that the presently identified brain changes are specifically associated with learning to read and not with general maturational brain changes. Results of this project inform us on specific brain changes associated with reading development and further analyses of this longitudinal data set will enable to characterize brain changes associated disturbances in learning to read and dyslexia.