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Corpus callosum microstructure indexes behavioral performance on dichotic listening task
Poster Session A, Wednesday, September 30, 11:00 am - 1:00 pm, Wangari Maathai
Gabriel Cler1,2, Hadeel Ershaid1, Amaia Carrión Castillo1, Garikoitz Lerma-Usabiaga1,3, Marie Lallier1; 1Basque Center on Cognition, Brain and Language, 2University of Washington, 3Ikerbasque - Basque Foundation for Science, Bilbao, Spain
Comprehending spoken language requires coordination of bilateral brain networks. Dichotic listening tasks typically produce a right-ear advantage (REA), in which participants report stimuli presented simultaneously to the right ear more accurately than those to the left. This effect is thought to reflect left hemisphere language dominance and the time required for interhemispheric transfer of left-ear inputs via the corpus callosum (CC) (Kimura, 1967; Westerhausen & Hugdahl, 2008). In this study, we examined the relationship between quantitative structural measures of myelin and behavioral performance on a dichotic listening task in multilingual, typically-developing children. Better myelinated CC fibers should support faster and more efficient interhemispheric transfer: left-ear input is initially processed in the right hemisphere and must cross the CC to reach the language-dominant left hemisphere; more efficient callosal transfer should allow left-ear signals to reach the left hemisphere more effectively, reducing the REA (Westerhausen & Hugdahl, 2008). We hypothesized that increased myelination of the CC would lead to a lower REA and that degree of multilingualism would modulate myelination of the CC. Thirty-two multilingual children aged 7-12 completed MR Fingerprinting (MRF), standard T1-weighted imaging (MP2RAGE), and behavioral assays of language and reading. MRF data were processed (toolbox by Liao & Cao) to produce quantitative T1 and T2 maps. T1w images were processed with FreeSurfer recon-all, and CC segmentations were registered to MRF native space. Mean T1 and T2 relaxation times were extracted from eroded CC masks to minimize partial volume effects. Hierarchical regression models tested whether CC microstructure predicted REA beyond age. Contrary to our hypothesis, lower quantitative T1 relaxation time (indicating greater myelination) in the posterior CC predicted stronger rather than reduced REA, independent of age (partial r=−0.48, p=.010; ΔR²=0.19 beyond age alone). A marginal trend was observed for anterior CC T1 (partial r=−0.36, p=.062). No associations were found for T2 relaxation time or normalized CC volume in either region; nor between degree of multilingualism and any expected variables. To examine possible effects beyond the CC, we ran an exploratory voxelwise GLM to determine the relationship of the quantitative T1s to REA while controlling for age (FSL randomise with TFCE). No clusters survived FWE correction. At an uncorrected threshold of p<.01, stronger REA was associated with lower T1 (greater myelination) in regions including left perisylvian cortex (inferior frontal gyrus, central opercular cortex, Heschl's gyrus), left dorsal white matter pathways (superior longitudinal fasciculus), and homologous right hemisphere regions. No clusters were found in the opposite direction. While these results should be interpreted cautiously, the spatial distribution (concentrated in perisylvian and dorsal language regions rather than uniformly distributed) suggests that stronger REA may reflect advanced myelination of the bilateral language network. Together, these results suggest that auditory lateralization in multilingual children indicates broader neural maturation of the bilateral language network rather than CC-specific interhemispheric transfer efficiency. The absence of multilingualism effects suggests that the degree of multilingual experience does not modulate this relationship in this age range, though ongoing data collection in children at risk for dyslexia will examine this further.
Topic Areas: Language Development/Acquisition, Multilingualism