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Poster C53, Friday, August 17, 10:30 am – 12:15 pm, Room 2000AB

Bilingualism interacts with age-related cortical thinning in children and adolescents

Christos Pliatsikas1, Vincent DeLuca1, Lotte Meteyard1, Michael Ullman2;1School of Psychology and Clinical Language Sciences, University of Reading, UK, 2Department of Neuroscience, Georgetown University, USA

Recent evidence suggests that learning and using a second language (L2) affects the structure of the adult cortex, even in individuals who started learning their L2 in adolescence. Specifically, various cortical regions related to language processing or executive control, such as the left superior, middle and inferior frontal gyri (SFG, MFG, IFG), the superior parietal lobule (SPL), the supramarginal gyrus (SMG), and several temporal regions, have been found to show increases in volume and/or thickness (Pliatsikas,in press) in L2 learners/users vs. monolinguals. However, the variability in the available evidence makes it unclear whether the observed differences are due to brain reorganisation because of late L2 learning and long-term L2 usage, or whether they also apply to very young speakers of two languages, and if so, how they interact with brain development. Studies looking at the brain structure of bilingual children remain scarce, but it has been shown that cortical thickness in some of these regions differs between bilingual children with balanced and unbalanced proficiency in their two languages (Archila-Suerte et al., 2018). It is a well-documented finding that cerebral cortex becomes thinner in developing children (Tamnes et al., 2010), with regions such as the IFG and MFG more affected than others (Fjell et al., 2009). Crucially, since the same regions have also been reported to be increased in size as a result of L2 learning/usage, it would be expected that bilingualism interacts with typical cortical thinning of these regions, possibly by delaying it. To test this hypothesis, we extracted cortical thickness data from children and adolescents reporting speaking one (n=1524) and two (n=394) languages from the PING database (http://pingstudy.ucsd.edu/). We used Generalised Additive Mixed Models to test the effect of Age and Bilingualism on cortical thickness, accounting for confounding variables such as sex, handedness, education, and household income. Our results revealed a significant main effect of Age for a large number of brain regions, showing development-related cortical thinning as per previous findings. Interestingly, significant Age*Bilingualism interactions were reported for bilateral SFG, SMG, IFG, SPL, the postcentral, precentral and paracentral gyri, and the precuneus (all ps<0.001). For all regions, monolinguals had steeper age slopes than bilinguals, demonstrating that slower cortical thinning for the latter group over the course of childhood and adolescence in regions related to the acquisition and handling of two languages. These results will be discussed against models on bilingualism-induced brain restructuring and recent suggestions about the applicability of critical periods in L2 learning in the face of neuroimaging data (DeLuca et al.,in press) References Archila-Suerte et al. (2018). Developmental Science, e12654. https://doi.org/10.1111/desc.12654 DeLuca et al (in press). Brain adaptations and neurological indices of processing in adult Second Language Acquisition: Challenges for the Critical Period Hypothesis. In J. Schwieter (Ed.), The Handbook of the Neuroscience of Multilingualism. Wiley- Blackwell. Fjell et al. (2009). Cerebral Cortex, 19(9), 2001–2012. https://doi.org/10.1093/cercor/bhn232 Pliatsikas (in press). Multilingualism and brain plasticity. In J. Schwieter (Ed.), The Handbook of the Neuroscience of Multilingualism. Wiley- Blackwell. Tamnes et al. (2010). Cerebral Cortex, 20(3), 534–548. https://doi.org/10.1093/cercor/bhp118

Topic Area: Multilingualism

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