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Corpus Callosum White Matter Microstructure and Language Abilities in Adults with Developmental Language Disorder
Poster Session A, Wednesday, September 30, 11:00 am - 1:00 pm, Wangari Maathai
Noelle Abbott1, Sophia Banel1, Gabriel Cler1,2; 1Department of Speech and Hearing Sciences, University of Washington, 2Basque Center on Cognition Brain and Language
Developmental Language Disorder (DLD) is a neurodevelopmental condition characterized by persistent language difficulties in the absence of known neurological causes (Bishop, 2017). Prior work has identified atypical bilateral language network activation in adults with DLD (Abbott et al., in press), yet structural white matter correlates remain poorly understood. The corpus callosum (CC), which supports interhemispheric communication between bilateral language regions, may play a critical role in DLD (Bartha-Doring et al., 2020). We examined white matter microstructure in adults with DLD compared to adults with typical language development (TD) and tested whether callosal integrity predicts language ability within group. Methods. Diffusion-weighted MRI data were collected from 46 adults (23 DLD, 23 TD). Groups were defined via the Fidler protocol, which uses an auditory directions and irregular spelling task in a weighted equation (Fidler et al., 2011). Diffusion-weighted images were preprocessed using FSL to generate diffusion tensor imaging parameters (e.g., fractional anisotropy [FA]) and the SMI Toolbox to calculate Standard Model of Diffusion parameters (e.g., f and p2, indexing axonal density and alignment respectively). Whole-brain tract-based spatial statistics (TBSS) generated a white-matter skeleton and identified regions of FA differing between groups. Tractography and tractometry were performed using pyAFQ, which identified white matter tracts, segmented them into 100 nodes, and extracted diffusion metrics. Profiles were analyzed across the middle 60% of each tract to minimize partial volume effects. Group differences in FA were assessed using node-wise linear regression with FDR correction across tracts. SMI parameters were examined within tracts to determine biological bases of FA differences. Results. TBSS identified reduced FA in the DLD group in the CC and in white matter appearing to relate to bilateral superior longitudinal fasciculus (SLF), left arcuate fasciculus, and the planum temporale. Tractometry between groups revealed a small but significant overall reduction in white matter FA in adults with DLD compared to TD adults (t=2.926, p=0.005). Node-wise analyses revealed CC-specific differences, wherein adults with DLD showed significantly reduced FA along the superior parietal, superior frontal, temporal, and occipital subdivisions. No significant node-wise differences were observed in the SLF or other language tracts. FA differences in the CC were partially explained by reduced p2 and f in the same regions, suggesting both reduced axonal organization and density. Within-group analyses revealed that FA-language correlations were specific to the DLD group, with callosal motor FA predicting spelling ability (r=0.445, p=0.033) and callosal occipital (r=0.462, p=0.026) and temporal (r=0.424, p=0.044) FA predicting following-directions task performance in DLD but not TD adults. Conclusion. Adults with DLD show reduced fiber organization and density along callosal subdivisions connecting bilateral frontal, parietal, and temporal regions. Critically, callosal white matter integrity predicts language performance specifically in the DLD group, suggesting that interhemispheric communication via the CC may be a structural mechanism relating to language difficulties in DLD, though whether these differences are causal or reflect differences in language learning and processing is unknown. These findings complement recent functional neuroimaging work and point to the CC as a key white matter pathway implicated in DLD in adulthood.
Topic Areas: Disorders: Developmental,