White matter and literacy: a dynamic system in flux

Abstract

Past studies have linked differences in white matter tissue properties to reading skills. However, these studies have reported a range of, sometimes conflicting, results. Some studies suggest that white matter properties act as individual-level traits predictive of reading skill, whereas others suggest that reading skill and white matter develop as a function of an individual's educational context. In the present study, we tested two hypotheses: a) that diffusion properties of the white matter reflect stable brain characteristics that relate to reading skills over development or b) that white matter plays a part in a dynamic system, linked with learning over time. To answer these questions, we examined the relationship between white matter and reading in a series of large-scale, single-observation datasets and a four-year longitudinal dataset. We find that gains in reading skill correspond to longitudinal changes in the white matter. However, in the single-observation datasets, we find no evidence for the hypothesis that individual differences in white matter predict reading skill. These findings highlight the link between dynamic processes in the white matter and learning.

Fiber-Specific Structural Properties Relate to Reading Skills in Children and Adolescents

“…We hypothesized that fixel-based metrics would be sensitive to variation in reading abilities especially in the left arcuate fasciculus, left inferior fronto-occipital fasciculus, and cerebellum. Unlike recent cross-sectional studies of fractional anisotropy that yielded few-to-no regions exhibiting significant FA-reading relationships or group differences in FA ( Moreau et al, 2018 ; Koirala et al, 2021 ; Economou et al, 2022 ; Meisler and Gabrieli, 2022 ; Roy et al, 2022 ), we found that higher FDC related to better single-word reading skills throughout the brain. However, FDC did not differ between those with and without reading disabilities.…”

“…Our results suggest that phonological skills, as opposed to lower-level visual and orthographic processing, may provide more of a bottleneck to single-word reading abilities in children. The present results are supported by a large-scale longitudinal study finding that fractional anisotropy of the left AF, but not ILF, covaries with single-word reading skill trajectories in children (Roy et al, 2022). This notion is also consistent with a behavioral study demonstrating that orthographic skills are more related with the ability to read longer passages, as opposed to single words (Barker et al, 1992).…”

“…Geeraert et al (2020 ) used principal component analysis to draw out white matter structural indices from several scalar maps, including metrics from DTI (such as FA) and neurite orientation dispersion and density imaging (NODDI; Zhang et al (2012 )), and found that variance in these measures were driven by age-related development, but not reading. Three large-scale cross-sectional studies using publicly available data sets found largely null associations between FA and reading skills in several tracts ( Koirala et al, 2021 ; Meisler and Gabrieli, 2022 ; Roy et al, 2022 ).…”

“…( 2012 )), and found that variance in these measures were driven by age-related development, but not reading. Three large-scale cross-sectional studies using publicly available data sets found largely null associations between FA and reading skills in several tracts ( Koirala et al, 2021 ; Meisler and Gabrieli, 2022 ; Roy et al, 2022 ).…”

“…Since white matter exhibits learning-driven plasticity and can also modulate neuronal firing patterns ( Fields, 2015 ; Xin and Chan, 2020 ), one may expect that functional variation, such as differences in reading ability, may be reflected by some white matter structural property ( Ramus et al, 2018 ; Protopapas and Parrila, 2018, 2019 ). The largely null findings in higher-powered meta-analyses ( Moreau et al, 2018 ) and large-scale studies ( Koirala et al, 2021 ; Meisler and Gabrieli, 2022 ; Roy et al, 2022 ) suggest that FA is not a specific enough metric to effectively capture this relationship in cross-sectional designs (however, see Van Der Auwera et al . ( 2021 ) and Roy et al .…”