Myelin Water Imaging Demonstrates Lower Brain Myelination in Children and Adolescents With Poor Reading Ability

Abstract

Magnetic resonance imaging (MRI) provides a means to non-invasively investigate the neurological links with dyslexia, a learning disability that affects one's ability to read. Most previous brain MRI studies of dyslexia and reading skill have used structural or diffusion imaging to reveal regional brain abnormalities. However, volumetric and diffusion MRI lack specificity in their interpretation at the microstructural level. Myelin is a critical neural component for brain function and plasticity, and as such, deficits in myelin may impact reading ability. MRI can estimate myelin using myelin water fraction (MWF) imaging, which is based on evaluation of the proportion of short T2 myelin-associated water from multiexponential T2 relaxation analysis, but has not yet been applied to the study of reading or dyslexia. In this study, MWF MRI, intelligence, and reading assessments were acquired in 20 participants aged 10-18 years with a wide range of reading ability to investigate the relationship between reading ability and myelination. Group comparisons showed markedly lower MWF by 16-69% in poor readers relative to good readers in the left and right thalamus, as well as the left posterior limb of the internal capsule, left/right anterior limb of the internal capsule, left/right centrum semiovale, and splenium of the corpus callosum. MWF over the entire group also correlated positively with three different reading scores in the bilateral thalamus as well as white matter, including the splenium of the corpus callosum, left posterior limb of the internal capsule, left anterior limb of the internal capsule, and left centrum semiovale. MWF imaging from T2 relaxation suggests that myelination, particularly in the bilateral thalamus, splenium, and left hemisphere white matter, plays a role in reading abilities. Myelin water imaging thus provides a potentially valuable in vivo imaging tool for the study of dyslexia and its remediation.

Myelin water fraction in relation to fractional anisotropy and reading in 10-year-old children

“…To date, only one study has directly investigated the relationship between MWF and reading ability. In a sample of 20 participants aged 10-18 years old, Beaulieu et al (2020) reported positive correlations between reading and MWF, as well as lower MWF in poor (n=7) compared to good readers (n=11) in several regions including bilateral thalamus, centrum semiovale, anterior and posterior limbs of the internal capsule and splenium of the corpus callosum. This study offers new insights into the relationship between myelin water and reading, however replication of these ndings is warranted given the small sample size, the wide age range and the selection of regions which are not typically considered part of the core reading circuitry.…”

Update on myelin imaging in neurological syndromes

“…Disrupted, altered or less effective connections between brain regions supporting academic learning are related to learning disabilities, such as dyslexia, which is linked to inefficient communication between brain regions. Significantly lower MWF values have been found in children categorized as 'poor readers', further supported by a significant positive correlation between MWF and age-standardized reading scores [15]. Recent work also found that students who showed greater improvement in working memory after cognitive intervention had higher baseline MWF [16].…”

Cortical asymmetries at different spatial hierarchies relate to phonological processing ability

“…This larger sample exhibited 10% missingness across predictor variables in the multiple imputation model, which included age, sex, research site, as well as standardized scores for phonological decoding (Word Attack [ 118 , 119 ]), real word identification (Letter–Word Identification [ 118 , 119 ]), reading comprehension (Passage Comprehension cloze task [ 118 , 119 ]), rapid naming [ 120 , 121 ], and verbal comprehension [ 122 , 123 ]. These measures were requested during multisite data collection, in part because they have been used in previous studies to demonstrate brain structure and behavior associations, particularly for the Word Attack phonological decoding measure [ 9 , 39 , 41 , 72 , 124 , 125 ]. There was 6% and 14% missingness in the pediatric and adult samples, with a low percentage of phonological decoding missingness (0.4%, 8%), respectively.…”