Neural Correlates of Developmental Dyslexia: A Multimodal Study of Typical and Atypical Reading

Abstract

Developmental dyslexia is the most common neurobehavioural disorder that can affect up to 17% of school-aged children. It is characterised by literacy difficulties in accurate and fluent word recognition. Previous research has made significant progress into studying the behavioural, cognitive and neurobiological causes of the reading disability. More recently, important advances into understanding the neural circuits and the aetiology of dyslexia has come from, respectively, brain imaging and genetic findings. Although neuroimaging studies have been able to identify the cortical areas involved in the reading deficit, the high heterogeneity in dyslexic traits still remains poorly investigated. The aim of this research was to expand on the previous findings by offering a thorough investigation of brain networks underlying complex symptoms of dyslexia. For this reason, a multimodal cognitive, genetic, structural and functional neuroimaging approach was employed. First, different dyslexic functional networks were identified by studying MEG resting state functional connectivity and network topology. In particular, an un-biased graph theory measure, the minimum spanning tree, was used to portray frequency specific connectomes in relation to fluency and genetic components. Second, a novel MEG paradigm was designed to delineate time-specific neural correlates and dynamic oscillatory activity in the first stages of reading processing, the prelexical orthographic visual word recognition, in typical and dyslexic readers. Third, structural connectivity, by means of diffusion tensor imaging (DTI), was investigated in typical and atypical readers. The outcome of each of these studies demonstrates how a correlational cognitive-genetic-neuroimaging method is fundamental to be able to distinguish neural mechanisms and brain networks underpinning different dyslexic phenotypes. Overall, the results of this work provide a strong case for the design and the application of a multimodal (cognitive, genetic, structural and functional neuroimaging) approach to examine neurobiological correlates of typical and atypical reading development, and better define the dyslexic continuum.