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Second Language Learning Related Structural White Matter Plasticity

Poster E66 in Poster Session E, Saturday, October 8, 3:15 - 5:00 pm EDT, Millennium Hall

Xuehu Wei¹, Helyne Adamson¹, Matthias Schwendemann¹, Tomás Goucha¹, Angela D. Friederici¹, Alfred Anwander; ¹Max Planck Institute for Human Cognitive and Brain Sciences

Introduction: Several studies have suggested that learning a second language (L2) in adulthood causes dynamic changes in the gray and white matter of the brain (e.g. Li et al., 2014, Cortex, 58, 301–324, Pliatsikas, C, 2020, Bilingualism, 23(2), 459–471). Changes related to lexical-semantic, phonological and syntactic L2-acquisition were found beyond the regions associated with native language processing with additional right-hemispheric involvement and changes in the interhemispheric communication. In this longitudinal study, we aimed to understand experience-dependent white matter plasticity during intensive second language learning in relation to the second language performance. Methods: 60 young healthy right-handed Arabic native speakers (mean age, 25.9 years; range, 19-34) were recruited for an intensive German course (5h/day, 5days/week) over a six-month period. After three and six months of language learning, we acquired high-resolution diffusion MRI. At the same time, each participant performed a standardized holistic second language proficiency test. Using probabilistic tractography, the structural connectivity between all language-related areas in both hemispheres were computed. We scaled language test scores from the two time-points to a common scale following the scaling method proposed by the Cambridge Test of English. We then assessed L2 proficiency using a Linear Mixed Effects (LME) model with language test scores at each time point as fixed effects. To localize the learning-induced connectivity change for specific subnetworks, we used Network-Based R-statistic LME models to test the relationship between brain network plasticity and L2-proficiency across the learning period (p-threshold = 0.01, K = 3000 permutations, Gracia-Tabuenca et al., 2020, bioRxiv, 11.07.373019). Results: We observed that L2 language proficiency showed significant improvement from three to six months. And the changes in L2 proficiency from three to six months were related to increased intra-hemispheric connectivity in several sub-networks known to be associated with lexical-semantic and phonological processing. These sub-networks include the bilateral parietal-temporal system and the right dorsal pathway between the inferior frontal gyrus and temporal regions. Additionally, we found a negative correlation between L2-proficiency and changes in interhemispheric connectivity via the anterior and posterior corpus callosum. Conclusions: The present study demonstrated that multiple white matter sub-networks show significant change during second language learning. The main effects were found in the lexical-semantic system in temporo-parietal regions of both hemispheres. This highlights a crucial role of the right hemisphere in second language learning. Additionally, we found a reduction in transcallosal connectivity, which might relate to a stronger specialization of both hemispheres for efficiently processing the newly acquired language. These findings demonstrate the experience-dependent structural plasticity in the human brain during second language learning, which is essential to better understand the interaction of environment, behavior, and language on shaping the human brain.

Topic Areas: Multilingualism, Meaning: Lexical Semantics