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Poster E66, Friday, November 10, 10:00 – 11:15 am, Harborview and Loch Raven Ballrooms

Cortical thickness differs between bilinguals and monolinguals according to age of acquisition

Hannah Claussenius-Kalman1, Pilar Archila-Suerte1, Kelly A. Vaughn1, Arturo E. Hernandez1;1University of Houston

This study aimed to investigate the relationship between second language (L2) age of acquisition (AoA) and brain structure by examining cortical thickness in a large group of bilinguals and monolinguals. Data were analyzed from eight fMRI studies at CAMRI at Baylor College of Medicine. Of 376 participants, brain scans of 364 participants were included. Six brain scans were removed due to reconstruction issues, five due to technical fMRI scanning issues, and one due to brain trauma. Brains were constructed and manually edited using FreeSurfer. Whole-brain analyses were conducted using ANOVA in QDEC to determine differences in cortical thickness according to AoA, which was grouped by simultaneous bilingual (AoA < 3; n = 26), early bilingual (AoA 4-6; n = 107), late bilingual (AoA > 7; n = 78), and monolingual (n = 153). Late bilinguals relative to monolinguals had increased cortical thickness in the left inferior parietal lobule (IPL), inferior temporal gyrus (ITG), transverse temporal gyrus (TTG), medial orbitofrontal cortex (OFC), superior frontal gyrus (SFG), right lateral occipital lobe, middle temporal gyrus (MTG), and bilateral superior temporal gyrus (STG). Late bilinguals relative to simultaneous bilinguals had increased cortical thickness in the bilateral IPL, left caudal middle frontal gyrus (MFG), SMG, medial OFC, right SFG, and lateral occipital lobe (FWE-corrected p < .05). No significant differences were found for monolinguals versus bilinguals, nor for monolingual versus simultaneous, monolingual versus early, simultaneous versus early, or early versus late. Using a large dataset, the present study confirms previous results showing differences in cortical thickness associated with bilingualism. Overall, increased cortical thickness for late bilinguals relative to monolinguals in the left SFG, IPL, and medial OFC may indicate connections to a fronto-parietal network. Frontal regions are commonly associated with cognitive control and working memory, while the parietal cortex is involved in visuospatial processing and attention. Research has shown that bilinguals have greater grey matter density in the left IPL (Stein et al., 2014), which is implicated in phonological working memory and lexical learning. In addition, differences in frontal and parietal regions were found for late bilinguals relative to simultaneous bilinguals, where late bilinguals had greater cortical thickness in the left SMG, medial OFC, caudal MFG (which encompasses the DLPFC), right SFG, and bilateral IPL. This is in line with models of bilingualism that associate the DLPFC and other frontal areas with language control and switching. One possible explanation is that the cortex, especially the frontal regions, finishes developing later than subcortical structures, so late bilinguals may rely on these structures more than simultaneous bilinguals during L2 acquisition (see sensorimotor hypothesis, Hernandez & Li, 2007). Finally, late bilinguals relative to monolinguals showed differences in temporal thickness (bilateral STG, right TTG, right MTG, and left ITG), but late bilinguals relative to simultaneous bilinguals did not. This may be due to prolonged plasticity of the temporal lobe. As a whole, these findings suggest a relationship between later AoA and the neuroanatomy of frontal and parietal areas, which are commonly associated with language processing and cognitive control.

Topic Area: Multilingualism

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