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Poster C65, Thursday, November 9, 10:00 – 11:15 am, Harborview and Loch Raven Ballrooms

Individual differences in age of acquisition predict fine-grained white matter microstructure in bilinguals

Emily Nichols1, Marc Joanisse1, Yue Gao2, Li Liu2;1University of Western Ontario, 2Beijing Normal University

There is an emerging consensus that bilingualism influences the structure of the white matter connections in the brain, especially in left- and right-hemisphere tracts commonly associated with language processing. However, there is appreciable variability in both the nature and direction of these differences, with studies variously observing higher or lower indices of connectivity in bilinguals compared to monolinguals, across a number of tracts in either the left or right hemisphere. The lack of clarity in this regard may stem from differences in analytic approach and sample groups. In the present study we compared fractional anisotropy (FA) of language-related white matter tracts in English-Mandarin bilinguals compared to monolingual controls. Individuals were scanned at 3 Tesla using diffusion-tensor imaging at 64 directions (voxel size: 2.083 x 2.083 x 2 mm; matrix: 96 x 96 x 68), aligned to a high resolution T1 MPRAGE scan (voxel size: 1 x 1 x 1 mm; matrix: 256 x 256 x 176). Individuals were also tested for proficiency in English and Mandarin, and completed demographic questionnaires including measures of language history and day-to-day usage. White matter analyses used automatic fiber quantification (AFQ) to identify and quantify subject-wise fiber tracts, including computing FA at multiple points along each tract. Groupwise comparisons showed significantly lower FA in bilinguals along sub-portions of left arcuate fasciculus (AF), left superior longitudinal fasciculus (SLF), left and right inferior fronto-occipital fasciculus (IFOF), and left inferior longitudinal fasciculus (ILF). One concern with these findings however, is that they are being driven by extraneous differences between groups, rather than bilingual status. We addressed this in follow-up analyses, where we examined whether individual differences in bilingual individuals’ age of acquisition (AoA) also showed a similar relationship to white matter FA. Concordant with the groupwise analyses, we found that FA increased as a function of AoA in these same white matter tracts, such that tracts of late bilingual tended to more closely resemble those of monolinguals.

Topic Area: Multilingualism

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