An Overview on Electrophysiological and Neuroimaging Findings in Dyslexia

Abstract

Objective: Dyslexia is a prevalent neurodevelopmental condition that is characterized by inaccurate and slow word recognition. This article reviews neural correlates of dyslexia from both electrophysiological and neuroimaging studies.
 Method: In this brief review, we provide electrophysiological and neuroimaging evidence from electroencephalogram (EEG) and magnetic resonance imaging (MRI) studies in dyslexia to understand functional and structural brain changes in this condition.
 Results: In both electrophysiological and neuroimaging studies, the most frequently reported functional impairments in dyslexia include aberrant activation of the left hemisphere occipito-temporal cortex (OTC), temporo-parietal cortex (TPC), inferior frontal gyrus (IFG), and cerebellar areas. EEG studies have mostly highlighted the important role of lower frequency bands in dyslexia, especially theta waves. Furthermore, neuroimaging studies have suggested that dyslexia is related to functional and structural impairments in the left hemisphere regions associated with reading and language, including reduced grey matter volume in the left TPC, decreased white matter connectivity between reading networks, and hypo-activation of the left OTC and TPC. In addition, neural evidence from pre-reading children and infants at risk for dyslexia show that there are abnormalities in the dyslexic brain before learning to read begins.
 Conclusion: Advances in comprehending the neural correlates of dyslexia could bring closer translation from basic to clinical neuroscience and effective rehabilitation for individuals who struggle to read. However, neuroscience still has great potential for clinical translation that requires further research.

Overt Word Reading and Visual Object Naming in Adults with Dyslexia: Electroencephalography Study in Transparent Orthography

“…Regarding findings of electrophysiological and neuroimaging studies, the most frequently reported are structural and functional impairments in dyslexia [34][35][36][37][38][39][40][41][42][43][44][45][46][47]. Aberrant activation reported for PD relates to the left hemisphere brain areas, including the cerebellar area, inferior frontal area, situated near Broca's area, implicated in motor speech production, a peri-sylvian temporo-parietal region implicated in speech comprehension, and inferior temporo-occipital region (very often referred as the visual word form area) implicated in fast word decoding.…”

“…The majority of ERP studies have been conducted on non-transparent orthographies (i.e., English, French, Portuguese) using covert reading and naming designs in adult PDs [35,40,64,81,87,89] and children with dyslexia [48,104] investigating pre-lexical, lexical and post-lexical stage of processing [35,40,47,59,64,81,87,89,91]. Lately, two studies on dyslexia have been conducted by using an overt design in adult PDs [56] and children with dyslexia [54] in non-transparent orthographies.…”