Voxel and surface based whole brain analysis shows reading skill associated grey matter abnormalities in dyslexia

Teija Kujala,Peter Palo-Oja,Anja Thiede,Paula Virtala,Aleksi J Sihvonen,Jussi Numminen,Marja Laasonen

doi:10.1038/s41598-021-89317-x

Abstract

Developmental dyslexia (DD) is the most prevalent neurodevelopmental disorder with a substantial negative influence on the individual’s academic achievement and career. Research on its neuroanatomical origins has continued for half a century, yielding, however, inconsistent results, lowered total brain volume being the most consistent finding. We set out to evaluate the grey matter (GM) volume and cortical abnormalities in adult dyslexic individuals, employing a combination of whole-brain voxel- and surface-based morphometry following current recommendations on analysis approaches, coupled with rigorous neuropsychological testing. Whilst controlling for age, sex, total intracranial volume, and performance IQ, we found both decreased GM volume and cortical thickness in the left insula in participants with DD. Moreover, they had decreased GM volume in left superior temporal gyrus, putamen, globus pallidus, and parahippocampal gyrus. Higher GM volumes and cortical thickness in these areas correlated with better reading and phonological skills, deficits of which are pivotal to DD. Crucially, total brain volume did not influence our results, since it did not differ between the groups. Our findings demonstrating abnormalities in brain areas in individuals with DD, which previously were associated with phonological processing, are compatible with the leading hypotheses on the neurocognitive origins of DD.

Highlights

Developmental dyslexia (DD) is the most prevalent neurodevelopmental disorder with a substantial negative influence on the individual’s academic achievement and career
No group differences were found in total grey matter (GM), white matter (WM), CSF, total intracranial volume (TIV), or total brain volume (Table 1)
There is an obvious need to understand the neural underpinnings of DD, which is highly prevalent and can have devastating academic, psychosocial, and psychiatric effects on the individual affected (e.g.5)

Summary

Introduction

Developmental dyslexia (DD) is the most prevalent neurodevelopmental disorder with a substantial negative influence on the individual’s academic achievement and career. Developmental dyslexia (DD) is a reading-skill impairment with a strong and multifactorial genetic c omponent[1], which may emerge irrespective of adequate intelligence and reading instruction[2] It is the most common neurodevelopmental disorder having a prevalence reported to range between 5–17.5%3 and 5–10%4. Meta-analyses summarizing the heterogenous voxel-based morphometry (VBM) findings have reported grey matter (GM) anomalies mainly in the left occipito-temporal and bilateral superior temporal and parietal areas as well as the cerebellum bilaterally[15,16,17]. The most recent meta-analysis, including 1164 participants across 18 studies, concluded, that even large-scale studies highlight a range of inconsistencies and limitations[14] According to this analysis the most robust finding in DD is reduced total brain volume, rendering the cortical anomalies associated with DD unsettled. Demographic Gender (male/female) Age (years) Education (years) Musical education (years) Morphological Grey matter volume (litres) White matter volume (litres) Cerebrospinal fluid volume (litres) Total intracranial volume (litres) Total brain volume (litres)

Methods

Results

Conclusion