PNAS:外语学不好, 基因:怪我咯

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为什么有些成年人很快就能掌握第二语言，而另一些人却表现得很困难？新一期美国《国家科学院学报》上发布的研究显示，这在一定程度上可能与基因有关。

刚从中国到美国华盛顿大学学习的79名大一新生参加了这项研究。这些学生平均年龄20岁，此前都未在国外生活过，其中44人参加了为期3周的英语沉浸式强化培训，另外35人作为对照组。

华盛顿大学的研究人员利用一种叫弥散张量成像的磁共振技术观测参与者的大脑语言回路连接情况。连接情况越好，意味着学习能力可能越强。结果显示，参与沉浸式强化培训的时间越长，大脑语言回路连接越好。但有些人的语言回路连接更好一些，有些人则稍差一些，显示出第二语言的学习存在个体化差异。

研究人员又分析了这些学生的DNA（脱氧核糖核酸）样本，发现一种叫COMT的基因变异与强化培训期间的大脑语言回路连接变化相关。COMT基因参与维持人脑中多巴胺和去甲肾上腺素等神经递质的水平。新研究显示，COMT基因有两种变异能加强语言回路连接。

总体上，COMT基因变异与大脑语言回路连接对一个成年人学好第二语言的影响占46％。研究人员表示，他们接下来将分析影响语言学习的其他因素。

负责研究的华盛顿大学的间宫赵屏告诉新华社记者：“我希望这项研究结果能让人们了解，在过了早期的发育‘关键期’后，为什么一些人学习第二语言很费劲，而另外一些人的学习却相对轻松。”

来源：新华社

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

Ping C. Mamiyaa, Todd L. Richardsb, Bradley P. Coec, Evan E. Eichlerc,d, and Patricia K. Kuhl

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.

http://www.pnas.org/content/early/2016/06/07/1606602113.long