The timing of language learning shapes brain structure associated with articulation
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We compared the brain structure of highly proficient simultaneous (two languages from birth) and sequential (second language after age 5) bilinguals, who differed only in their degree of native-like accent, to determine how the brain develops when a skill is acquired from birth versus later in life. For the simultaneous bilinguals, gray matter density was increased in the left putamen, as well as in the left posterior insula, right dorsolateral prefrontal cortex, and left and right occipital cortex. For the sequential bilinguals, gray matter density was increased in the bilateral premotor cortex. Sequential bilinguals with better accents also showed greater gray matter density in the left putamen, and in several additional brain regions important for sensorimotor integration and speech–motor control. Our findings suggest that second language learning results in enhanced brain structure of specific brain areas, which depends on whether two languages are learned simultaneously or sequentially, and on the extent to which native-like proficiency is acquired.
KeywordsBilingualism Magnetic resonance imaging Voxel-based morphometry Gray matter density Age of acquisition Putamen Motor cortex Accent Plasticity Skill learning Brain structure
Jennifer Soles assisted with the experimental setup and subject recruitment. Megan Callahan assisted with the quantitative language assessment. The study was supported by funds from the Blema and Arnold Steinberg Family Foundation and grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) to D. Klein and V. Gracco, the Social Sciences and Humanities Research Council of Canada (SSHRC) to Baum, Gracco, and Klein, and a Vanier Canada Doctoral Scholarship to J. Berken (NSERC).
Compliance with ethical standards
Conflict of interest
The authors declare no competing financial interests.
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