The effects of individual differences in bilingual experience on cognitive control networks

The number of children learning a second language at school in the UK has dramatically decreased in the past 10 years, even though learning a second language has many benefits. It broadens understanding of different cultures, improves literacy and employability, and importantly, may also be good for the brain. Being bilingual appears to have a positive effect on a collection of high level cognitive abilities, often referred to as executive functions such as response inhibition and task switching. Speaking another language might also slow down cognitive decline by delaying the onset of dementia. The reason for these effects is thought to be the constant inhibition of one language when speaking the other and frequent language switches. Moreover, it is known that poor executive functions are linked to social problems including antisocial behaviour or addiction. Improving executive functions via language learning might potentially lessen such problems. Despite a growing and large body of evidence in favour of executive advantages, some studies have not been able to replicate the findings. One often suggested explanation for these inconsistencies is the heterogeneity of the bilingual population. Bilingual speakers differ with respect to when they started to learn their second language, how fluently they speak it and how often they use each language. All these factors have been found to be independently related to executive function abilities, but no study to date has systematically investigated these factors. Identifying the precise characteristics that bring out a bilingual advantage is crucial in identifying the conditions under which improved executive control behaviour can be achieved.

The proposed study will use a multimodal approach to provide a systematic and thorough investigation into the effects of bilingual key characteristics (second language proficiency, age of second language acquisition, and language use) on executive control behaviour as well as the underlying brain differences. We will obtain from bilingual and monolingual speakers measures of individual differences in language proficiency and use, measures of behaviour in executive function tasks, and of brain differences. For the latter, we will measure differences in brain structure (grey and white matter) and communication between brain areas (functional brain connectivity). Participants will be tested on the two executive functions that have most strongly been associated with bilingual advantage: inhibition and switching ability. Participants' brain structure will be measured using voxel-based morphometry (VBM), their structural connectivity using diffusion imaging (DTI). Bilingual functional brain connectivity will for the first time be measured using electro-encephalography (EEG), a particularly good real-time measure of brain communication. Furthermore, we will determine the neural sources of the EEG functional connectivity measures by testing a subset of both bilingual and monolingual participants additionally on one inhibition task and one switching task while simultaneously measuring their EEG and blood-oxygen-level dependent (BOLD) signals via functional magnetic resonance imaging (fMRI). In contrast to EEG, fMRI is an excellent measure of where in the brain processing differences occur. Combined EEG-fMRI is a novel approach to the bilingual advantage question. Critically, all these measures will be acquired in the same participants. This will enable us to describe the complex interactions between behaviour, brain structure, and neural functions in executive function tasks and how those interactions are modulated by the individual participant characteristics. It will be the first time that such a multidisciplinary and comprehensive approach is used to investigate the brain networks underlying bilingualism and the benefits in executive control they might support.

Our research has the potential to impact on UK policies on language teaching and uptake of languages in schools. The lack of knowledge of foreign languages in the UK has been identified as both a serious economic and social concern. A publication of The British Chambers of Commerce ("Exporting is good for Britain", 2012) reports that 96% of the companies responding to a survey did not have any language ability for the market that they serve. A paper by the British Council ("Languages for the Future", 2014) reports that 75% of adult UK population cannot hold a conversation in any of the ten languages most important for the UK economy. Furthermore, The British Academy has stressed that the knowledge of languages is not only important for trade and economy, but also for greater intercultural understanding and interactions as well as social well-being at home and overseas ("Language Matters More and More", 2011). But despite these calls for language learning and teaching, the number of pupils choosing to learn a language continues to decrease (Education Development Trust: "Language Trends 2015/16"). The number of pupils taking A-levels in languages has been falling over the recent years, with only 3.8% of students learning a language beyond a basic level ("Languages for the Future", British Council, 2014). Two of the main reasons for this trend is the reluctance of pupils to study a language and the perceived lack of importance of languages compared to other subjects by schools, pupils and parents (Education Development Trust: "Language Trends 2015/16"). What is needed then is a change in awareness of the importance and benefits of speaking another language.

Impact A. Foreign language learning in schools
The potential economic advantages of language learning unlikely convince the individual, because only a minority of pupils are interested in a career related to international trade. The knowledge that speaking another language might provide personal cognitive advantages and a potential cognitive reserve in case of Alzheimer and stroke might be a more compelling argument. The proposed research into cognitive advantages of bilingualism therefore has the potential to positively affect the uptake of language learning in schools.

Impact B. Educational practice and policy
In addition, since our research aims at a better understanding of what exact circumstances (early language acquisition, second language proficiency etc.) lead to cognitive advantages, its findings have the potential to inform educational practice and policy with regards to, for instance, the age and intensity at which languages are taught.

Impact C. Addiction and mental health
Our findings have also the potential to impact on the well-being of the U.K. in other ways. Executive functions such as inhibition have been linked to addiction (e.g., Baler & Volkow, 2006) as well as mental health issues such as depression (e.g., Tavares et al., 2007) and anxiety (e.g., Shields et al., 2016). All these problems are very costly to the U.K. society. Drug addiction has been estimated to cost society £15.4 billion (National Treatment Agency for Substance Misuse, 2013) and mental illness £105.2 billion a year (Centre for Mental Health, 2010). Improving executive functions via language learning might potentially alleviate problems such as mental health issues and reduce the costs to society and improve well-being.

Impact D. Training of Research Fellow
Another important impact of this project will be the further training of the Research Fellow in an array of sophisticated scientific (e.g. simultaneous EEG/fMRI)and transferable skills (e.g. public engagement). The training will be accomplished by PIs during the supervision of the RF as well as via specialized methodological training and seminars available within the School of Psychology at Birmingham University. Note that the School has particular research strengths in cutting edge EEG and fMRI methodologies.