Genetic variants related to dopamine functioning (e.g., the ANKK1/TaqIa polymorphism within the DRD2 gene and the Val158Met polymorphism within the COMT gene) have previously been shown to predict cognitive flexibility and learning (e.g., Colzato et al., 2010; Stelzel et al., 2010). Additionally, researchers have found that these genetic variants may also predict second language learning (Mamiya et al., 2016), although this relationship may change across the lifespan (Sugiura et al., 2011). The current study examined the role of the ANKK1/TaqIa and Val158Met polymorphisms along with age of second language acquisition (AoA) in order to predict levels of bilingual proficiency in Spanish-English bilinguals. Results indicated a three-way interaction such that the relationship between the genetic variants and bilingual proficiency depended on AoA. At earlier AoAs, having the genetic variant associated with higher levels of subcortical dopamine (A1+) predicted the highest levels of bilingual proficiency. At later AoAs, individuals with the genetic variant associated with cortical dopamine levels that are balanced between stability and flexibility (Val/Met) predicted the highest levels of bilingual proficiency. These results fit with theories about the development of language as a subcortical process early in life and as a cortical process later in life (Hernandez & Li, 2007), as well as the importance of both stability and flexibility in bilingual language development (Green & Abutalebi, 2013). Finally, this study raises questions about the direction of causality between bilingualism and cognitive control, which is central to the debate over the "bilingual advantage."

中文翻译：

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成为平衡、熟练的双语者：从习得年龄和遗传背景的预测

与多巴胺功能相关的遗传变异（例如，DRD2 基因内的 ANKK1/TaqIa 多态性和 COMT 基因内的 Val158Met 多态性）先前已被证明可以预测认知灵活性和学习（例如，Colzato 等人，2010 年；Stelzel 等人., 2010)。此外，研究人员发现，这些遗传变异也可以预测第二语言学习（Mamiya 等人，2016 年），尽管这种关系可能会在整个生命周期中发生变化（Sugiura 等人，2011 年）。目前的研究检查了 ANKK1/TaqIa 和 Val158Met 多态性与第二语言习得年龄 (AoA) 的作用，以预测西英双语者的双语熟练程度。结果表明存在三向相互作用，因此遗传变异与双语能力之间的关系取决于 AoA。在早期的 AoA 中，具有与更高水平的皮质下多巴胺 (A1+) 相关的遗传变异预测双语能力的最高水平。在后期的 AoA 中，具有与皮质多巴胺水平相关的遗传变异的个体在稳定性和灵活性之间保持平衡（Val/Met）预测双语能力水平最高。这些结果符合关于语言发展在生命早期作为皮层下过程和生命后期作为皮层过程的理论（Hernandez & Li, 2007），以及稳定性和灵活性在双语语言发展中的重要性（Green &阿布塔莱比，2013 年）。最后，这项研究提出了关于双语和认知控制之间因果关系方向的问题，这是“双语优势”辩论的核心。