White matter microstructural plasticity associated with educational intervention in reading disability

Abstract

Children's reading progress typically slows during extended breaks in formal education, such as summer vacations. This stagnation can be especially concerning for children with reading difficulties or disabilities, such as dyslexia, because of the potential to exacerbate the skills gap between them and their peers. Reading interventions can prevent skill loss and even lead to appreciable gains in reading ability during the summer. Longitudinal studies relating intervention response to brain changes can reveal educationally relevant insights into rapid learning-driven brain plasticity. The current work focused on reading outcomes and white matter connections, which enable communication among the brain regions required for proficient reading. We collected reading scores and diffusion-weighted images at the beginning and end of summer for 41 children with reading difficulties who had completed either 1st or 2nd grade. Children were randomly assigned to either receive an intensive reading intervention (n = 26; Seeing Stars from Lindamood-Bell which emphasizes orthographic fluency) or be deferred to a wait-list group (n = 15), enabling us to analyze how white matter properties varied across a wide spectrum of skill development and regression trajectories. On average, the intervention group had larger gains in reading compared to the non-intervention group, who declined in reading scores. Improvements on a proximal measure of orthographic processing (but not other more distal reading measures) were associated with decreases in mean diffusivity within core reading brain circuitry (left arcuate fasciculus and left inferior longitudinal fasciculus) and increases in fractional anisotropy in the left corticospinal tract. Our findings suggest that responses to intensive reading instruction are related predominantly to white matter plasticity in tracts most associated with reading.

Keywords: DWI; dyslexia; intervention; plasticity; reading; white matter.

Fig. 1.

Tracts produced by TRACULA analyzed in the present study, overlaid on top of a fractional anisotropy image. Only the left hemispheric bundles are visualized for bilateral tracts. Pictured data come from a single representative participant.

Fig. 2.

Changes in Symbol Imagery Test (SIT; left) and Composite Reading Index (right) scores for intervention (purple) and non-intervention (yellow) participants. Pairedt-tests were used to compare pre and post scores within groups, and two-samplet-tests were used to compare scores at a given time point across groups. Significant tests (p< 0.05) are annotated in the figure.

Fig. 3.

Partial regression plots relating changes in tract microstructure to changes in standardized SIT scores. Confounds included age at first scan, sex, and motion indices at each time point. Values on axes are residuals after accounting for nuisance regressors in the model. Models with an uncorrectedp< 0.05 across all participants are shown. For MD, these include models of the left ILF and ILF laterality index (top), and left AF and AF laterality index (middle). For FA, this includes the left CST (bottom). No test reached this threshold with the composite reading index. Purple dots represent intervention participants, and yellow does represent non-intervention participants. The black solid lines and effect sizes represent the fit across all participants, and the purple dashed lines and effect sizes represent the best when considering only intervention participants. †:p< 0.1, *:p< 0.05, **: pFDR < 0.05. Abbreviations: AF - Arcuate Fasciculus; ILF - Inferior Longitudinal Fasciculus; CST - Corticospinal Tract.