Brain white matter structure and COMT gene are linked to second-language learning in adults

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 S econd-language learning in adulthood is becoming increasingly prevalent as globalization advances. Previous studies show that gray matter volume and density are related to foreign language speech learning (1, 2), and that the degree of volumetric change in an individual predicts the level of foreign language proficiency achieved by that person (3, 4). Recent studies using diffusion tensor imaging (DTI) techniques further show that diffusion properties of brain white matter structure are correlated with foreign language learning (5-7). One of these studies demonstrated that the changes in diffusion properties predicted students' second-language proficiency at the end of a language immersion program (7). These findings suggest that the properties of brain structure change with the acquisition of a new language, and that the adult human brain is capable of tissue reorganization in response to intense use of a new language after the putative "critical period."What remains unknown is whether and how genetic factors are related to brain white matter fiber-tract properties as learning ensues. Cumulative evidence using DTI analysis has suggested that brain white matter fiber-tract properties are related to skill learning ...

The bilingual adaptation: How minds accommodate experience.

“…These results were found at both time points. Supporting the role of bilingualism in these effects, Mamiya, Richards, Coe, Eichler, and Kuhl (in press) reported a correlation between higher FA values in the superior longitudinal fasciculus and length of time spent in a language immersion program for Chinese students learning English.…”

No Evidence That Schizophrenia Candidate Genes Are More Associated With Schizophrenia Than Noncandidate Genes

“…Yet candidate gene research continues in other fields, despite these issues. For example, a Google Scholar search performed on July 31, 2016 for “COMT” generated three thousand search results from 2016 alone, many of which are classic candidate gene association studies; the first five phenotypes from this search were circadian preferences(32), affective well-being across the lifespan(33), cognitive outcomes after electroconvulsive therapy(34), effect of opioid treatment on pain relief(35), and second-language learning in adults(36). It is of course possible that these and other traits are exceptions to what we now know about complex traits studied to date by GWAS, for which thousands of risk variants exist, each which explain a very small amount of variation (37).…”

Understanding structural plasticity in the bilingual brain: The Dynamic Restructuring Model

“…Note that no changes are usually reported in any subcortical structures or the cerebellum in these studies. In terms of effects in the white matter, it appears that additional language training increases white matter integrity by means of decreasing its isotropic diffusivity in tracts that provide connectivity between frontal, parietal, temporal and subcortical language-related regions, and in both hemispheres (Hosoda et al, 2013;Mamiya, Richards, Coe, Eichler, Kuhl, Geschwind & Paus, 2016;Schlegel, Rudelson & Tse, 2012;Xiang, van Leeuwen, Dediu, Roberts, Norris & Hagoort, 2015). These primarily include tracts connecting frontal to temporal and/or parietal regions, both ventral tracts implicated in semantic and syntactic processing (Inferior Fronto-Occipital Fasciculus -IFOF, Inferior Longitudinal Fasciculus -ILF, Uncinate Fasciculus -UF), and dorsal tracts implicated in the processing of phonology and complex syntax (Arcuate Fasciculus -AF, Superior Longitudinal Fasciculus -SLF) (Friederici & Gierhan, 2013), but also the Corpus Callosum (CC), which is crucial for interhemispheric communication and cognitive control (Felton, Vazquez, Ramos Nuñez, Greene, Macbeth & Hernandez, 2017).…”