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White matter differences in individuals with developmental dysgraphia
Poster Session D, Saturday, October 26, 10:30 am - 12:00 pm, Great Hall 3 and 4
Romi Sagi1, Brenda Rapp2, Michal Ben-Shachar1; 1Bar-Ilan University, 2Johns Hopkins University
Producing written language is a fundamental aspect of daily communication, yet the neural pathways that support it are still not well understood, and far less studied compared to reading. Functional MRI studies have revealed that spelling requires information transfer within a distributed, left-dominant cortical network (Planton et al., 2013; Purcell et al., 2011). Diffusion MRI (dMRI) studies have shown that left ventral and bilateral dorsal white matter pathways are associated with spelling performance (Banfi et al., 2019; Cheema et al., 2022; Gebauer et al., 2012; Neophytou et al., 2023; Sagi et al., 2024). Recent data suggest that lexical aspects of spelling map to left ventral pathways, while sublexical aspects map to dorsal pathways (Cheema et al., 2022; Sagi et al., 2024). Here, we evaluated the white matter integrity of dorsal and ventral language-related pathways in two right-handed individuals with severe developmental dysgraphia: father (RBT, 56y) and son (TBT, 19y). Developmental dysgraphia in these participants was accompanied by developmental surface dyslexia. In particular, they experienced difficulties in spelling and reading orthographically irregular words compared to regular words and pseudowords, indicating a specific developmental difficulty in acquiring or retrieving lexical-orthographic representations. Other cognitive skills, including spoken language, memory and executive functions, were typical or superior to age norms. Microstructural properties of white matter pathways in each participant were compared with matched control groups (N=12 for RBT, N=22 for TBT). dMRI scans were acquired on a 3T Philips scanner using a single-shot EPI sequence along 64 directions. Data were preprocessed with tensor modeling at the voxel level, coupled with whole-brain deterministic tractography. Tracts of interest were identified bilaterally using automated segmentation tools; dorsally: the arcuate fasciculus (AF) and superior longitudinal fasciculus-III (SLF-III); ventrally: the inferior longitudinal fasciculus (ILF) and inferior fronto-occipital fasciculus (IFOF). For each participant and tract, fractional anisotropy (FA) values were averaged and lateralization indices were calculated. FA values and lateralization indices were compared between each participant and their matched control group using a two-tailed Crawford-Howell t-test. Both father and son showed an overall pattern of reduced FA in certain dorsal and ventral left-hemisphere tracts, coupled with right-biased lateralization in both streams. Specifically, both participants showed reduced FA in the left ILF compared with matched controls. Significant right-biased lateralization indices (vs. controls, p<0.05) were observed in the father in a dorsal tract (SLF-III) and in the son in both dorsal and ventral tracts (AF and ILF). These results are consistent with previous dMRI findings showing spelling associations with both dorsal and ventral streams in typical adults. Reduced anisotropy in the left ILF and right-biased lateralization overall may reflect poor lexical-orthographic spelling processes mediated by the left ventral stream and greater reliance on the right-hemisphere dorsal pathways for sublexical spelling. Our findings shed light on the neural system that supports spelling and broaden the understanding of developmental spelling deficits. Given the close relationships between spelling and reading, further work will be required to distinguish the contribution of the underlying white matter pathways to spelling and reading difficulties, respectively.
Topic Areas: Writing and Spelling, Disorders: Developmental