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

Abstract

Atypical structural properties of the brain’s white matter bundles have been associated with failing reading acquisition in developmental dyslexia. Because these white matter properties may show dynamic changes with age and orthographic depth, we examined fractional anisotropy (FA) along 16 white matter tracts in 8- to 11-year-old dyslexic (DR) and typically reading (TR) children learning to read in a fairly transparent orthography (Dutch). Our results showed higher FA values in the bilateral anterior thalamic radiations of DRs and FA values of the left thalamic radiation scaled with behavioral reading-related scores. Furthermore, DRs tended to have atypical FA values in the bilateral arcuate fasciculi. Children’s age additionally predicted FA values along the tracts. Together, our findings suggest differential contributions of cortical and thalamo-cortical pathways to the developing reading network in dyslexic and typical readers, possibly indicating prolonged letter-by-letter reading or increased attentional and/or working memory demands in dyslexic children during reading.

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

“…Individuals with dyslexia have smaller and differently shaped LGN (Giraldo-Chica et al, 2015). Fractional anisotropy in the left and right thalamus has correlated with reading ability (Lebel et al, 2013) and diffusion tensor tractography has identified differences in thalamic connections in individuals with dyslexia (Fan et al, 2014;Müller-Axt et al, 2017;Žarić et al, 2018;Tschentscher et al, 2019). These studies align with our observations of lower MWF in the anterior limb of the internal capsule which contains axons connecting the thalamus and frontal lobe.…”

“…Since the earliest DTI papers demonstrating correlations of reading ability with DTI parameters (Klingberg et al, 2000;Nagy et al, 2004;Beaulieu et al, 2005;Deutsch et al, 2005;Niogi and McCandliss, 2006), a vast literature over the last 15 years has highlighted key white matter connections presumed to underlie the potentially inefficient communication or ''disconnection'' between brain regions in dyslexia (see Ben-Shachar et al, 2007;Vandermosten et al, 2012b; for comprehensive reviews and a meta-analysis of earlier DTI papers). These DTI reading findings are not limited to English with similar results across multiple languages (Qiu et al, 2008;Steinbrink et al, 2008;Thiebaut de Schotten et al, 2014;Zhang et al, 2014;Cui et al, 2016;Takeuchi et al, 2016;Zhao et al, 2016;de Moura et al, 2016;Vanderauwera et al, 2017;Su et al, 2018;Žarić et al, 2018;Moulton et al, 2019). While many of these studies reported DTI changes in the left temporoparietal white matter, other bilateral regions and the corpus callosum have also shown associations with reading, implicating a broader network.…”

The interplay of socio-economic status represented by paternal educational level, white matter structure and reading

“…This approach can enhance our understanding of microscopic white matter structure and macrostructural influences [84]. Third, although the present study included in vivo tractography of six white matter pathways in the left hemisphere, future research should include the investigation of the relation between parental education level, word reading and structural organization of other pathways that have been related to reading and dyslexia, such as the thalamic radiations [85–88]. Finally, the relation between paternal educational level and reading was restricted to word reading, and no relation was found with pseudo-word reading.…”

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

“…Reduced FA in these tracts has been observed in both children and adults with dyslexia [Klingberg et al, 2000, Richards et al, 2008, Steinbrink et al, 2008, Carter et al, 2009, Christodoulou et al, 2017, Su et al, 2018, Žarić et al, 2018, children with reduced pre-reading language skills [Saygin et al, 2013], and even infants from families with a history of dyslexia . In contrast, multiple other studies have either failed to find this difference or had the opposite findings of increased FA in the left-hemisphere tracts [Arrington et al, 2017[Arrington et al, , Žarić et al, 2018.…”

“…Reduced FA in these tracts has been observed in both children and adults with dyslexia (Klingberg et al, 2000;Richards et al, 2008;Steinbrink et al, 2008;Carter et al, 2009;Christodoulou et al, 2017;Su et al, 2018;Žarić et al, 2018), children with reduced pre-reading language skills (Saygin et al, 2013), and even infants from families with a history of dyslexia . Finally, the stark differences in FA correlation strengths between SWE and PDE were unexpected.…”