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Contributed by Patricia K. Kuhl, May 7, 2016 (sent for review September 29, 2015; reviewed by Daniel H. Geschwind and Tomáš Paus)
Significance
Second-language learning in adulthood is a topic of wide interest given globalization, and levels of proficiency are highly variable among individuals. Here we demonstrate a significant correlation between individuals’ white matter fiber-tract properties in language areas and participation in an English language immersion program. Moreover, we found that this relationship was influenced by genetic variation (catechol-O-methyltransferase gene). Individuals with the Methionine (Met)/Valine (Val) or Val/Val genotype, but not the Met/Met genotype, showed higher fractional anisotropy and lower radial diffusivity during immersion. Values of brain measurements reversed after the immersion ended. These results suggest that second-language learning is influenced by an interaction between brain white matter structure and genetic factors.
Abstract
Adult human brains retain the capacity to undergo tissue reorganization during second-language learning. Brain-imaging studies show a relationship between neuroanatomical properties and learning for adults exposed to a second language. However, the role of genetic factors in this relationship has not been investigated. The goal of the current study was twofold: (i) to characterize the relationship between brain white matter fiber-tract properties and second-language immersion using diffusion tensor imaging, and (ii) to determine whether polymorphisms in the catechol-O-methyltransferase (COMT) gene affect the relationship. We recruited incoming Chinese students enrolled in the University of Washington and scanned their brains one time. We measured the diffusion properties of the white matter fiber tracts and correlated them with the number of days each student had been in the immersion program at the time of the brain scan. We found that higher numbers of days in the English immersion program correlated with higher fractional anisotropy and lower radial diffusivity in the right superior longitudinal fasciculus. We show that fractional anisotropy declined once the subjects finished the immersion program. The relationship between brain white matter fiber-tract properties and immersion varied in subjects with different COMT genotypes. Subjects with the Methionine (Met)/Valine (Val) and Val/Val genotypes showed higher fractional anisotropy and lower radial diffusivity during immersion, which reversed immediately after immersion ended, whereas those with the Met/Met genotype did not show these relationships. Statistical modeling revealed that subjects’ grades in the language immersion program were best predicted by fractional anisotropy and COMT genotype.
Footnotes
- ↵1To whom correspondence should be addressed. Email: pkkuhl{at}u.washington.edu.
Author contributions: P.C.M. and P.K.K. designed research; P.C.M. and T.L.R. performed research; P.C.M., T.L.R., B.P.C., and E.E.E. analyzed data; and P.C.M. and P.K.K. wrote the paper.
Reviewers: D.H.G., University of California, Los Angeles; and T.P., University of Toronto.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1606602113/-/DCSupplemental.
Freely available online through the PNAS open access option.
- aInstitute for Learning & Brain Sciences, University of Washington, Seattle, WA 98195;
- bDepartment of Radiology, University of Washington, Seattle, WA 98195;
- cDepartment of Genome Sciences, University of Washington, Seattle, WA 98195;
- dHoward Hughes Medical Institute, University of Washington, Seattle, WA 98195
Contributed by Patricia K. Kuhl, May 7, 2016 (sent for review September 29, 2015; reviewed by Daniel H. Geschwind and Tomáš Paus)
Significance
Second-language learning in adulthood is a topic of wide interest given globalization, and levels of proficiency are highly variable among individuals. Here we demonstrate a significant correlation between individuals’ white matter fiber-tract properties in language areas and participation in an English language immersion program. Moreover, we found that this relationship was influenced by genetic variation (catechol-O-methyltransferase gene). Individuals with the Methionine (Met)/Valine (Val) or Val/Val genotype, but not the Met/Met genotype, showed higher fractional anisotropy and lower radial diffusivity during immersion. Values of brain measurements reversed after the immersion ended. These results suggest that second-language learning is influenced by an interaction between brain white matter structure and genetic factors.
Abstract
Adult human brains retain the capacity to undergo tissue reorganization during second-language learning. Brain-imaging studies show a relationship between neuroanatomical properties and learning for adults exposed to a second language. However, the role of genetic factors in this relationship has not been investigated. The goal of the current study was twofold: (i) to characterize the relationship between brain white matter fiber-tract properties and second-language immersion using diffusion tensor imaging, and (ii) to determine whether polymorphisms in the catechol-O-methyltransferase (COMT) gene affect the relationship. We recruited incoming Chinese students enrolled in the University of Washington and scanned their brains one time. We measured the diffusion properties of the white matter fiber tracts and correlated them with the number of days each student had been in the immersion program at the time of the brain scan. We found that higher numbers of days in the English immersion program correlated with higher fractional anisotropy and lower radial diffusivity in the right superior longitudinal fasciculus. We show that fractional anisotropy declined once the subjects finished the immersion program. The relationship between brain white matter fiber-tract properties and immersion varied in subjects with different COMT genotypes. Subjects with the Methionine (Met)/Valine (Val) and Val/Val genotypes showed higher fractional anisotropy and lower radial diffusivity during immersion, which reversed immediately after immersion ended, whereas those with the Met/Met genotype did not show these relationships. Statistical modeling revealed that subjects’ grades in the language immersion program were best predicted by fractional anisotropy and COMT genotype.
- genetic variation
- short-term plasticity
- dopamine
Footnotes
- ↵1To whom correspondence should be addressed. Email: pkkuhl{at}u.washington.edu.
Author contributions: P.C.M. and P.K.K. designed research; P.C.M. and T.L.R. performed research; P.C.M., T.L.R., B.P.C., and E.E.E. analyzed data; and P.C.M. and P.K.K. wrote the paper.
Reviewers: D.H.G., University of California, Los Angeles; and T.P., University of Toronto.
The authors declare no conflict of interest.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1606602113/-/DCSupplemental.
Freely available online through the PNAS open access option.
Brain–gene interaction in second-language learning
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