Whereas some bilinguals have one language that is dominant, others attain high proficiency in both languages. This variation is likely explained by a combination of environmental and genetic factors; however, there is a lapse in research on the neural underpinnings of bilingual proficiency. No study to date has examined how highly proficient bilingualism that is balanced relates to brain morphology in adults. Our present study analyzed the brains of 200 Spanish-English bilingual adults. Bilingual proficiency was measured and weighted by the degree of balance across the two languages. It was found that having higher dual language proficiency was related to thinner cortex in two regions: the left anterior prefrontal cortex (PFC) and the right anterior cingulate cortex (ACC). Neither English nor Spanish proficiency alone could account for neuroanatomical differences. Our findings suggest that thinner cortex of the left anterior PFC and the right ACC in adults with highly proficient, balanced bilingualism is how the adult brain reflects a lifetime of learning to flexibly adapt and utilize both languages and suggests the involvement of these structures in maintaining and increasing dual language proficiency.

中文翻译：

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高度熟练、平衡的双语能力与两个认知控制区域的皮层较薄有关

有些双语者只有一种语言占主导地位，而其他人则精通两种语言。这种变异可能是由环境和遗传因素共同解释的。然而，关于双语能力的神经基础的研究存在失误。迄今为止，还没有研究检查过平衡的高度熟练的双语与成年人的大脑形态之间的关系。我们目前的研究分析了 200 名西班牙语-英语双语成年人的大脑。双语能力通过两种语言之间的平衡程度来衡量和加权。研究发现，具有较高的双语能力与两个区域的皮层较薄有关：左前前额叶皮层 (PFC) 和右前扣带回皮层 (ACC)。单独的英语和西班牙语水平都不能解释神经解剖学的差异。我们的研究结果表明，在具有高度熟练、平衡的双语能力的成年人中，左前 PFC 和右 ACC 的较薄皮层是成年人大脑如何反映一生学习灵活适应和使用两种语言的方式，并表明这些结构参与维持和提高双语能力。