No evidence for systematic white matter correlates of dyslexia: An Activation Likelihood Estimation meta-analysis

Abstract

Dyslexia is a prevalent neurodevelopmental disorder, characterized by reading and spelling difficulties. Beyond the behavioral and functional correlates of this condition, a growing number of studies have explored structural differences between individuals with dyslexia and typically developing individuals. To date, findings remain disparate - some studies suggest differences in fractional anisotropy (FA), an indirect measure of white matter integrity, whereas others do not identify significant disparities. Here, we synthesized the existing literature on this topic by conducting a meta-analysis of Diffusion Tensor Imaging (DTI) studies investigating white matter correlates of dyslexia via voxel-based analyses (VBA) of FA. Our results showed no reliable clusters underlying differences between dyslexics and typical individuals, after correcting for multiple comparisons (false discovery rate correction). Because group comparisons might be too coarse to yield subtle differences, we further explored differences in FA as a function of reading ability, measured on a continuous scale. Consistent with our initial findings, reading ability was not associated with reliable differences in white matter integrity. These findings nuance the current view of profound, structural differences underlying reading ability and its associated disorders, and suggest that their neural correlates might be more subtle than previously thought.

A Large-Scale Investigation of White Matter Microstructural Associations with Reading Ability

“…Despite the general trend of higher FA relating to better reading and modest agreement in reading tract outcomes, a recent meta-analysis showed no evidence for systemic FA disruptions in dyslexia [Moreau et al, 2018]. Small cohort sizes, inhomogeneous acquisition parameters, and diversity in processing and analytical methods may underlie the inconsistencies in past results , Moreau et al, 2018, Schilling et al, 2021.…”

“…Despite the general trend of higher FA relating to better reading and modest agreement in reading tract outcomes, a recent meta-analysis showed no evidence for systemic FA disruptions in dyslexia [Moreau et al, 2018]. Small cohort sizes, inhomogeneous acquisition parameters, and diversity in processing and analytical methods may underlie the inconsistencies in past results , Moreau et al, 2018, Schilling et al, 2021. To address this, we leveraged the large database from the Healthy Brain Network [Alexander et al, 2017] to investigate white matter microstructural correlates of individual differences in single-word and single-nonword aptitude in children with diverse reading abilities.…”

Atypical White Matter Connectivity in Dyslexic Readers of a Fairly Transparent Orthography

“…Other group differences have been reported in FA values of the corpus callosum, including the body, splenium, and isthmus ( Frye et al, 2008 ; Richards et al, 2008 ; Welcome and Joanisse, 2014 ), the left inferior longitudinal fasciculus (ILF; connecting the ventral occipital to the anterior temporal lobe) and the IFOF (connecting the ventral occipital lobe and the orbitofrontal cortex) ( Rimrodt et al, 2010 ; Lebel et al, 2013 ; Marino et al, 2014 ). Most of these studies also report significant relations between diffusion weighted measures and diverse reading-related skills (but see Moreau et al, 2018a , b ).…”

No evidence for cerebellar abnormality in adults with developmental dyslexia

“…Candidate genes for dyslexia and specific language impairment have been shown to be related to white matter structure (Marino et al 2014 ; Scerri et al 2012 ). Nevertheless, a recent meta-analysis did not find consistent differences in local FA between subjects with and without dyslexia (Moreau et al 2018 ). Further studies on white matter connectivity between the cerebellum and the cerebral cortex are needed, in which challenges related to small sample sizes, differences in methods and individual anatomical heterogeneity need to be addressed.…”