Structural and functional connectivity in the bilingual brain across the lifespan: how experience shapes neurology and cognition

双语作为一种体验能够极大地改变大脑结构和认知，首先是灰质的增加，然后是白质完整性的增加，最后是皮层下和白质结构的重新正常化1。功能连接的变化已被预测，一些人发现双语者对大脑前部的依赖较少，功能网络在大脑中分布更广泛，将依赖转移到更后部的区域2。研究还发现，双语者的大脑主要功能网络之间更容易相互作用，其中额顶叶网络和默认模式网络会对其他网络的激活做出反应2-5。大脑的结构变化是否必然导致功能变化一直存在争议，因为在看似不存在结构连接的情况下发现了一些功能连接。对双语者进行了单独的结构1,7-10和功能2,11-14连接分析，结果表明两者都受到语言体验的各种因素的影响。静息态功能磁共振成像研究发现，双语者参与认知和语言控制的网络之间的连接性增强11,15，这为双语者中神经效率的提高提供了可能的解释，这意味着他们像单语者一样需要更少的认知努力来完成任务12。另一项脑电图研究发现，第二语言熟练程度可以调节双语者的注意力控制，这表明双语提供的任何认知效应可能存在于更多的范围内，而不是二分群体效应16。静息状态脑电图数据表明，双语会改变静息大脑节律，甚至可以预测个人的语言学习率17,18。 RS-EEG 也可用于功能连接分析19,20，尽管这些分析尚未在双语人群中进行，而且在他们之间进行的结构与功能连接比较分析也很少8,9。拟议研究的目的有三个：首先，比较双语者的结构和功能连接，并确定动态重组模型1预测的结构变化是否与功能变化相对应。这将通过使用预先存在的数据集，使用扩散张量成像进行结构分析，使用静息态功能磁共振成像进行功能分析来实现。其次，比较双语群体和单语群体之间的功能连通性。为此，将使用第一手收集的静息态脑电图测量结果。第三，确定功能连接的任何差异是否会影响完成认知任务时的神经效率。为了实现这一目标，将在经过语言修改的侧翼任务期间获取 ERP 读数。这也将从研究的 RS-EEG 部分的相同参与者那里直接收集。

Bilingualism as an experience has the capacity to drastically change brain structure and cognition, with initial increases in grey matter, followed by increases in white matter integrity, and finally, renormalisation of subcortical and white matter structures1. Changes in functional connectivity as a result have been predicted, with some finding that bilinguals rely less on the anterior portion of the brain and that the functional networks are more widely spread across the brain, shifting reliance to more posterior areas2. The brain's major functional networks have also been found to interact with each other more readily in bilinguals, with the frontoparietal and default mode networks responding to the activation of the other2-5. Whether structural changes in the brain necessarily lead to functional changes has been debated6, as some functional connections have been found where structural connections seemingly do not exist. In bilinguals, separate structural1,7-10 and functional 2,11-14 connectivity analyses have been conducted, with findings indicating that both are affected by various factors of the language experience.Resting-state fMRI studies found increased connectivity in bilinguals between the networks involved in cognitive and language control11,15, providing a possible explanation for increased neural efficiency also found in bilinguals, meaning that they require less cognitive effort to complete tasks as monolinguals12. Another EEG study found that second-language proficiency modulates control of attention in bilinguals, indicating that any cognitive effects that bilingualism provides may exist on more of a spectrum than as a dichotomous group effect16. Resting-state EEG data has shown that bilingualism changes resting brain rhythms, and can even predict an individual's rate of language learning17,18. RS-EEG can also be used for functional connectivity analyses19,20, though these analyses are yet to be conducted on bilingual populations, with very few comparative structural versus functional connectivity analyses having been conducted amongst them either8,9.The aims of the proposed study will be threefold: Firstly, to compare structural and functional connectivity in bilinguals, and determine whether structural changes predicted by the Dynamic Restructuring Model1 correspond with functional changes. This will be achieved using diffusion tensor imaging for structural analysis, and resting-state fMRI for functional analysis, using a pre-existing dataset. Secondly, to compare functional connectivity between bi- and monolingual groups. For this, resting-state EEG measurements will be used, collected first-hand. And thirdly, to determine whether any differences in functional connectivity affect neural efficiency when completing cognitive tasks. ERP readings will be taken during a language-modified Flanker task to achieve this aim. This will also be collected first-hand from the same participants included in the RS-EEG portion of the study.