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Structural and Functional Differences between Monolingual and Bilingual Young Adults

Ashley Chung-Fat-Yim (York University), Matthias Berkes (York University), Laura Mesite (Harvard Graduate School of Education), Buddhika Bellana (Baycrest Rotman Research Institute), Gigi Luk (Harvard Graduate School of Education), and Ellen Bialystok (York University)

ashc88@yorku.ca

Bilingualism; Task switching; fMRI; White matter; TBSS

Previous research has reported behavioral differences between monolingual and bilingual participants in executive control but the brain structures underlying those differences remain largely unknown. Neuroimaging studies have found overlapping circuits for linguistic and nonlinguistic control in bilinguals, but no study to date has examined this in both monolingual and bilingual participants. Hence, we compared behavioral performance, functional connectivity, and brain structures of young adults who were unbalanced but proficient bilinguals and monolinguals who had minimal use of a second language on a verbal and nonverbal switching task in fMRI. Fourteen monolingual and 17 English-French bilingual young adults participated. Groups differed in French proficiency, (Bilingual = 90.2%, Monolingual = 19.8%, t = 18.72, p < .001) and French usage (Bilingual = 30.9%, Monolingual= 0.40%, t = 6.69, p < .001). Behavioral results showed equivalent group performance on the nonverbal task but slower performance by bilinguals in the verbal task. Analysis of DTI data showed that bilinguals had higher fractional anisotropy (FA) than monolinguals in association tracts in the left hemisphere, specifically in the superior longitudinal fasciculus, inferior longitudinal fasciculus and inferior fronto-occipital fasciculus (corrected p < .05). No area showed higher FA in monolinguals than bilinguals. The higher FA values for bilinguals in these regions are similar to regions found in studies with children[1,2], young adults[3], and older adults[4]. Functional seed partial least squares revealed that monolinguals and bilinguals had different functional connectivity with left temporal regions when engaging in verbal switching, but similar networks when the two groups were engaging in nonverbal switching. These results contribute to our understanding of the brain basis of performance differences shown between monolinguals and bilinguals.

 

References

[1] Mohades, S. G., Struys, E., Van Schuerbeek, P., Mondt, K., Van De Craen, P., & Luypaert, R. (2012). DTI reveals structural differences in white matter tracts between bilingual and monolingual children. Brain Research, 1435, 72–80.

[2] Mohades, S. G., Van Schuerbeek, P., Rosseel, Y., Van De Craen, P., Luypaert, R., & Baeken, C. (2015). White-matter development is different in bilingual and monolingual children: A longitudinal DTI study. PLOS one, 10(2), e0117968.

[3] Pliatsikas, C., Moschopoulou, E., & Saddy, J. D. (2015). The effects of bilingualism on the white matter structure of the brain. Proceedings of the National Academy of Sciences of the United States of America, 112(5), 1334–1337.

[4] Luk, G., Bialystok, E., Craik, F. I. M., & Grady, C. L. (2011). Lifelong bilingualism maintains white matter integrity in older adults. Journal of Neuroscience, 31, 16808–16813.

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