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Neural basis of bilingual language control
Abstract
Acquiring and speaking a second language increases demand on the processes of language control for bilingual as compared to monolingual speakers. Language control for bilingual speakers involves the ability to keep the two languages separated to avoid interference and to select one language or the other in a given conversational context. This ability is what we refer with the term “bilingual language control” (BLC). It is now well established that the architecture of this complex system of language control encompasses brain networks involving cortical and subcortical structures, each responsible for different cognitive processes such as goal maintenance, conflict monitoring, interference suppression, and selective response inhibition. Furthermore, advances have been made in determining the overlap between the BLC and the nonlinguistic executive control networks, under the hypothesis that the BLC processes are just an instantiation of a more domain‐general control system. Here, we review the current knowledge about the neural basis of these control systems. Results from brain imaging studies of healthy adults and on the performance of bilingual individuals with brain damage are discussed. Acquiring and speaking a second language (L2) increases demand on the processes of language control for bilingual as compared to monolingual speakers. Language control for bilingual speakers involves the ability to keep the two languages separated to avoid interference and to select one language or the other in a given conversational context. Here, we review the current knowledge about the neural basis of these control systems. Results from brain imaging studies of healthy adults and on the performance of bilingual individuals with brain damage are discussed.
... Moreover, the phenomenon of bilingualism presents an intriguing case for studying grey matter's adaptability (Gallo et al., 2020). Managing two languages has been shown to impact the brain structurally; bilingual individuals often demonstrate greater grey matter volumes in regions associated with language, motor skills, and executive functions (Calabria et al., 2018;Wong et al., 2016). This is evidenced by neuroimaging studies that compare bilinguals to monolinguals, revealing significantly higher grey matter density in bilinguals in both the frontal and parietal lobes-areas crucial for executive control (Grundy et al., 2017). ...
... Despite these challenges, the reviewed studies consistently suggest that bilinguals demonstrate greater neural adaptability and enhanced efficiency in executive functioning, especially in tasks that necessitate the management of conflicting cognitive processes (Calabria et al., 2018;Grundy et al., 2017;Zhang & Wang, 2007). However, these observations must be carefully weighed against the methodological limitations inherent in the tools used to measure brain activity and the interpretative challenges they present (O'Connor & Zeffiro, 2019). ...
Research on bilingualism has traditionally focused on its effects on language proficiency, yet a significant gap exists in understanding its broader cognitive impacts, particularly regarding executive functions and brain structure. This study aims to bridge that gap by examining the multifaceted influences of bilingualism on cognitive function, incorporating historical and philosophical perspectives to provide a comprehensive analysis. Using a systematic literature review approach, supported by neuroimaging studies, this research explores how bilingualism enhances brain plasticity and executive functions, such as attentional control and task-switching. Historical analysis reveals the shift from early 20th-century deficit views of bilingualism to the recognition of its cognitive advantages. Philosophical discussions further contextualize these findings, addressing the ethical considerations of cognitive enhancement and the mind-brain relationship in bilingual contexts. The results suggest that bilingualism confers distinct cognitive benefits, reshaping both brain structure and function. Based on these findings, this study offers key recommendations for improving future research methodologies, emphasizing the need for more diverse and standardized studies, and suggests practical counseling approaches that account for the psychological and philosophical complexities of bilingual identity. These insights challenge traditional views on cognitive development and have significant implications for educational policies, counseling strategies, and future neuroscience research.
... The nature of the interaction between executive functions and semantic processing has been investigated extensively in the literature, in studies devoted to bilingual language processing (e.g. Calabria et al., 2018;Coderre et al., 2016;Linck et al., 2008), multimodal semantic processing (e.g. Pérez et al., 2020), the role of individual differences in suppression in the processing of semantic associations (Boudewyn et al., 2012), or to the comparison of the involvement of inhibitory control in referential context use in language comprehension and production (Dick et al., 2019;Linck et al., 2008;Pérez et al., 2020;Trude & Nozari, 2017). ...
This event-related potentials study focused on whether extensive practice of inhibitory control in a conflict task affects semantic processing/decisions in a subsequent language task. Participants took part in two 40-min sessions of the Simon task with either low or high inhibitory demands, each followed by a relatedness judgement task with strongly related, weakly related, and unrelated word pairs. The N400 in the relatedness judgement task was unaffected by inhibitory demands of the preceding Simon task. However, the late frontal positivity for weakly related pairs was enhanced relative to the other two conditions only after the low inhibitory demands Simon task, indicating a difference in the inhibition of the expected strongly related words between the two sessions. This suggests that the mechanisms underlying semantic facilitation for weakly related pairs operate at the decision stage and these can be modulated by inhibitory control demands in a preceding non-linguistic conflict task.
... In light of these findings, a promising future direction would be to incorporate neuroimaging data, which may provide critical information on the functional integrity of the language system and-unique to bilinguals-the interaction between L1 and L2 language networks and the concomitant integrity of control regions that can influence language processing and recovery in bPWA. [58][59][60] Furthermore, using an explainable ML tool (ie, SHAP), we observed the critical influence of UL severity on CLG and its interaction with cognitive factors, aspects overlooked in recent meta-analyses. 28 Relatedly, our cognition feature was also a key predictor in both the TLI and CLG analyses independently. ...
BACKGROUND
Predicting treated language improvement (TLI) and transfer to the untreated language (cross-language generalization, CLG) after speech-language therapy in bilingual individuals with poststroke aphasia is crucial for personalized treatment planning. This study evaluated machine learning models to predict TLI and CLG and identified the key predictive features (eg, patient severity, demographics, and treatment variables) aligning with clinical evidence.
METHODS
Forty-eight Spanish-English bilingual individuals with poststroke aphasia received 20 sessions of semantic feature-based naming treatment in either their first or second language. Comprehensive language, cognitive, and background bilingual experience assessments were administered pre- and post-treatment. Sixteen curated features spanning demographics, language abilities, cognition, and bilingual experience were used as inputs to 6 machine learning algorithms to predict treatment responders versus nonresponders and CLG vs no CLG.
RESULTS
The top 2 machine learning models achieved F1 scores of 0.767±0.153 for TLI and 0.790±0.172 for CLG. Interpretability analyses revealed that aphasia severity in the trained language, education, and cognitive performance were key predictors of TLI. Aphasia severity in the untreated language and cognitive performance emerged as influential features of CLG. These aligned with expectations based on prior literature.
CONCLUSIONS
For the first time, machine learning models reveal that factors such as patient severity and demographics predict TLI and CLG after therapy in Spanish-English bilingual individuals with poststroke aphasia. Consideration of both treated and untreated language severity, as well as cognitive assessment performance, when forecasting treatment outcomes in an underserved population such Spanish-English stroke survivors, can meaningfully impact their short-term and long-term clinical care.
... This difference is known as switching costs (i.e., switching costs = switchrepeat), reflecting local language control (also referred to as local control) over a restricted set of items in memory (e.g., specific lexical items) from the non-target language, exerted by bilinguals on a trial-by-trial basis. In addition, bilinguals exert greater language control globally (i.e., global control) over repeat trials in the dual language contexts compared to trials named in the single-language contexts, resulting in slower naming speed on repeat trials, a phenomenon known as mixing costs (i.e., mixing costs = repeatsingle; e.g., Calabria et al., 2018;Christoffels et al., 2007;de Bruin & Xu, 2023;Ma et al., 2016;Wang et al., 2022). Therefore, language control in bilingual language production is often considered a processing mechanism common but unique to bilinguals. ...
Previous research has mainly explored the relationship between bilingual language control and domain-general cognitive control through behavioral correlations, often revealing epiphenomenal links rather than causality. This study utilizes transcranial magnetic stimulation (TMS) to investigate the causal roles of the left inferior frontal gyrus (LIFG) and left posterior temporal lobe (LPTL) in these processes among 33 unbalanced Chinese-English bilinguals. Continuous theta burst stimulation was applied in separate sessions, with vertex stimulation as a control. Our results demonstrate that LIFG stimulation significantly increased switching costs in non-verbal switching tasks, highlighting its role in domain-general cognitive control. Conversely, LPTL stimulation did not affect switching or mixing costs in language or non-verbal switching tasks, suggesting no causal involvement. However, it reduced reaction times during language switching tasks, underscoring its specialization in language processing. These findings highlight potential distinctions between the neural mechanisms of bilingual language control and domain-general cognitive control, particularly in the LIFG.
... Whyatt (2019) also points out that the translator's cognitive effort differs for L1 and L2. In bilingualism studies, Calabria et al. (2018) state that processing demands for individuals with limited language proficiency were particularly taxing, thus indicating a relationship between level of language proficiency and cognitive processing. ...
Advanced language proficiency is a requirement for public service interpreting, and yet, research has not described this construct holistically in interpreting studies. Previous studies have suggested that public service interpreters primarily have a migration background and asymmetrical language proficiency. The present study reports findings of these aspects from a questionnaire that was conducted to investigate the linguistic background of Spanish-Swedish public service interpreters in Sweden. A total of 118 Spanish-Swedish interpreters answered the questionnaire. Results show that the interpreters have asymmetrical language proficiency but do not primarily have a migration background. Moreover, it is indicated that asymmetrical language proficiency and migration background have an impact on the likelihood of public service interpreters being state-authorized. However, there is a need for further research on these aspects to better understand details regarding both public service interpreters in Sweden and public service interpreters internationally.
... It is generally assumed that the suppression of the non-target language relies on inhibitory control, which is a central component of executive functions which underlies the ability to suppress prepotent automatic responses and information which is not relevant for achieving a certain goal (e.g., Abutalebi & Green, 2007;Calabria et al., 2018;Declerck & Philipp, 2015;Green, 1998;Kroll et al., 2008). ...
... [153][154][155][156][157][158][159][160] ated with controlling the use of the target language in a given conversational context, without interference of the non-target language (bilingual language control). [8][9][10] This mechanism of bilingual language control is associated with the use of a complex set of mechanisms for inhibitory control. 11 Several factors, distinct but interacting, are thought to influence the different cortical representations of language in bilinguals, including the age of acquisition, L2 proficiency and L1/L2 exposure. ...
Background
Primary progressive aphasia (PPA) is a language-based dementia, causing progressive decline of language functions. Transcranial direct current stimulation (tDCS) can augment effects of speech-and language therapy (SLT). However, this has not been investigated in bilingual patients with PPA.
Objective
We evaluated the case of Mr. G., a French (native language, L1)/Dutch (second language, L2)-speaking 59-year-old male, with logopenic PPA, associated with Alzheimer’s disease pathology. We aimed to characterize his patterns of language decline and evaluate the effects of tDCS applied to the right posterolateral cerebellum on his language abilities and executive control circuits.
Methods
In a within-subject controlled design, Mr. G received 9 sessions of sham and anodal tDCS combined with semantic and phonological SLT in L2. Changes were evaluated with an oral naming task in L2, the Boston Naming Task and subtests of the Bilingual Aphasia Test in in L2 and L1, the Stroop Test and Attention Network Test, before and after each phase of stimulation (sham/tDCS) and at 2-month follow-up.
Results
After anodal tDCS, but not after sham, results improved significantly on oral naming in L2, with generalization to untrained tasks and cross-language transfer (CLT) to L1: picture naming in both languages, syntactic comprehension and repetition in L2, and response times in the incongruent condition of the Attention Network Test, indicating increased inhibitory control.
Conclusions
Our preliminary results are the first to indicate that tDCS applied to the cerebellum may be a valuable tool to enhance the effects of SLT in bilingual patients with logopenic PPA.
... Language-related regions of interest (ROIs) were regions commonly identified as being involved in bilingual language control (e.g., Abutalebi & Green, 2016;Calabria et al., 2018;Gallo et al., Note: We do not report additional language data for participants' native language (L1), given that additional L1 language data were not provided by all participants in the subsample. In addition, we do not report additional language data for participants' languages past their third language, given that too few participants in the subsample reported knowing more than three languages. ...
We examined brain and cognitive reserve related to bilingualism in older adults with, or at-risk for, Alzheimer's disease (AD) from the Canadian Consortium on Neurodegeneration in Aging and the Quebec Consortium for the Early Identification of Alzheimer's Disease. We used surface-based morphometry methods to measure cortical thickness and volume of language-related and AD-related brain regions. We did not observe evidence of brain reserve in language-related regions. However, reduced hippocampal volume was observed for monolingual, but not bilingual, older adults with AD. Thus, bilingualism is hypothesized to contribute to reserve in the form of brain maintenance in the context of AD.
... In a different study, structural expansions of the cerebellum were also observed, accompanied by greater efficiency in processing second language grammatical rules (Pliatsikas et al., 2014). The cerebellum is linked to essential areas of the language control network and is pertinent in speech production and comprehension (Calabria et al., 2018). It underlies the learning and processing of grammar which are functions particularly taxing in the early days of acquiring a new language. ...
Think the human brain stops transforming in adulthood? You might want to think again! Contrary to popular belief, the human brain continues to change throughout our lifetime in response to the various experiences that we acquire. One such experience is the use of more than one language – an activity many of us already engage in in our daily lives. Join us in this chapter as we debunk the misconception of a static adult brain and delve into the evidence of multilingualism-induced neuroplasticity.
A neglected question regarding cognitive control is how control processes might detect situations calling for their involvement. The authors propose here that the demand for control may be evaluated in part by monitoring for conflicts in information processing. This hypothesis is supported by data concerning the anterior cingulate cortex, a brain area involved in cognitive control, which also appears to respond to the occurrence of conflict. The present article reports two computational modeling studies, serving to articulate the conflict monitoring hypothesis and examine its implications. The first study tests the sufficiency of the hypothesis to account for brain activation data, applying a measure of conflict to existing models of tasks shown to engage the anterior cingulate. The second study implements a feedback loop connecting conflict monitoring to cognitive control, using this to simulate a number of important behavioral phenomena.
The present functional magnetic resonance imaging (fMRI) study investigated influences of language contexts on inhibitory control and the underlying neural processes. Thirty Cantonese–Mandarin–English trilingual speakers, who were highly proficient in Cantonese (L1) and Mandarin (L2), and moderately proficient in English (L3), performed a picture-naming task in three dual-language contexts (L1-L2, L2-L3, and L1-L3). After each of the three naming tasks, participants performed a flanker task, measuring contextual effects on the inhibitory control system. Behavioral results showed a typical flanker effect in the L2-L3 and L1-L3 condition, but not in the L1-L2 condition, which indicates contextual facilitation on inhibitory control performance by the L1-L2 context. Whole brain analysis of the fMRI data acquired during the flanker tasks showed more neural activations in the right prefrontal cortex and subcortical areas in the L2-L3 and L1-L3 condition on one hand as compared to the L1-L2 condition on the other hand, suggesting greater involvement of the cognitive control areas when participants were performing the flanker task in L2-L3 and L1-L3 contexts. Effective connectivity analyses displayed a cortical-subcortical-cerebellar circuitry for inhibitory control in the trilinguals. However, contrary to the right-lateralized network in the L1-L2 condition, functional networks for inhibitory control in the L2-L3 and L1-L3 condition are less integrated and more left-lateralized. These findings provide a novel perspective for investigating the interaction between bilingualism (multilingualism) and inhibitory control by demonstrating instant behavioral effects and neural plasticity as a function of changes in global language contexts.
Bilingualism can delay the onset of dementia symptoms and has thus been characterized as a mechanism for cognitive or brain reserve, although the origin of this reserve is unknown. Studies with young adults generally show that bilingualism is associated with a strengthening of white matter, but there is conflicting evidence for how bilingualism affects white matter in older age. Given that bilingualism has been shown to help stave off the symptoms of dementia by up to four years, it is crucial that we clarify the mechanism underlying this reserve. The current study uses diffusion tensor imaging (DTI) to compare monolinguals and bilinguals while carefully controlling for potential confounds (e.g., I.Q., MMSE, and demographic variables). We show that group differences in Fractional Anisotropy (FA) and Radial Diffusivity (RD) arise from multivariable interactions not adequately controlled for by sequential bivariate testing. After matching and statistically controlling for confounds, bilinguals still had greater axial diffusivity (AD) in the left superior longitudinal fasciculus than monolingual peers, supporting a neural reserve account for healthy older bilinguals.
How does the brain process and control languages that are learned at a different age, when proficiency in all these languages is high? Early acquired strong languages are likely to have higher baseline activation levels than later learned less-dominant languages. However, it is still largely unknown how the activation levels of these different languages are controlled, and how interference from an irrelevant language is prevented. In this magnetoencephalography (MEG) study on language switching during auditory perception, early Finnish-Swedish bilinguals (N=18) who mastered English with high proficiency after childhood were presented with spoken words in each of the three languages, while performing a simple semantic categorisation task. Switches from the later learned English to either of the native languages resulted in increased neural activation in the superior temporal gyrus (STG) 400-600 ms after word onset (N400m response), whereas such increase was not detected for switches from native languages to English or between the native languages. In an earlier time window of 350-450 ms in the inferior frontal gyrus (IFG), English non-switch trials showed higher activation levels, pointing to ongoing inhibition of the native languages during the use of English. Taken together, these asymmetric switch costs suggest that native languages are suppressed during the use of a non-native language, despite the receptive nature of the present language task. This effect seems to be mostly driven by age of acquisition or language exposure, rather than proficiency. Our results indicate that mechanisms of control between two native languages differ from those of a later learned language, as upbringing in an early bilingual environment has likely promoted automatisation of language control specifically for the native languages.
In a recent review, Mukadam, Sommerlad, and Livingston (2017) argue that bilingualism offers no protection against cognitive decline. The authors examined the results of 13 studies (five prospective, eight retrospective) in which monolinguals and bilinguals were compared for cognitive decline and onset of dementia symptoms. Analysis of four of the five prospective studies resulted in the conclusion that there was no difference between monolinguals and bilinguals, whereas seven of the eight retrospective studies actually showed bilingualism to result in a four-to-five year delay of symptom onset. The authors decided to ignore the results from the retrospective studies in favor of those from the prospective studies, reasoning that the former may be confounded by participants' cultural background and education levels. In this commentary, we argue that most of these studies actually controlled for these two variables and still found a positive effect of bilingualism. Furthermore, we argue that the meta-analysis of the prospective studies is not complete, lacking the results of two crucial reports. We conclude that the literature offers substantial evidence for a bilingual effect on the development of cognitive decline and dementia.
Until recently, cognitive science virtually ignored the fact that most people of the world are bilingual. During the past ten years this situation has changed markedly. There is now an appreciation that learning and using more than one language is the more natural circumstance of cognition. As a result, there is a wealth of new research on second-language learning and bilingualism that provides not only crucial evidence for the universality of cognitive principles, but also an important tool for revealing constraints within the cognitive architecture. In this volume, Judith Kroll and Annette de Groot have brought together the scientists at the forefront of research on second-language learning and bilingualism to present chapters that, rather than focusing simply on their own research, provide the first comprehensive overviews of this emerging field. Bilingualism provides a lens through which each of the central questions about language and cognition can be viewed. The five sections of this book focus on different facets of those questions: How is language acquired when infants are exposed to multiple-language input from birth, and how is it acquired when adults are required to learn a second language after early childhood? How do adult bilinguals comprehend and produce words and sentences when their two languages are potentially always active and in competition with one another? What are the neural mechanisms that underlie proficient bilingualism? What are the general consequences of bilingualism for cognition and for language and thought? This handbook will be essential reading for cognitive psychologists, linguists, applied linguists, and educators who wish to better understand the cognitive basis of bilingualism and the logic of experimental and formal approaches to language science.
Research on the neural bases of bilingual language control has largely overlooked the role of preparatory processes, which are central to cognitive control. Additionally, little is known about how the process involved in global language selection may differ from those involved in the selection of words and morpho-syntactic rules for manipulating them. These processes were examined separately in an fMRI experiment, with an emphasis on understanding how and when general cognitive control regions become activated. Results of region-of-interest analyses on 23 early Spanish-English bilinguals showed that the anterior cingulate cortex (ACC) was primarily engaged during the language preparation phase of the task, whereas the left prefrontal (DLPFC) and pre-supplementary motor areas showed increasing activation from preparation to execution. Activation in the basal ganglia (BG), left middle temporal lobe, and right precentral cortical regions did not significantly differ throughout the task. These results suggest that three core cognitive control regions, the ACC, DLPFC, and BG, which have been previously implicated in bilingual language control, engage in distinct neurocognitive processes. Specifically, the results are consistent with the view that the BG "keep track" of the target language in use throughout various levels of language selection, that the ACC is particularly important for top-down target language preparation, and that the left prefrontal cortex is increasingly involved in selection processes from preparation through task execution.
Speaking more than one language is associated with neurocognitive benefits in seniors (Alladi et al. 2013). Few studies however have tested this hypothesis directly by comparing bilingual seniors who vary in chronological age. We report a Voxel-Based Morphometry (VBM) study showing cumulative effects of age on grey matter volume (GMV) in brain structures that are involved in cognitive control in bilingual seniors and found no differences in RT or accuracy between bilingual and monolingual seniors on a behavioral test of cognitive control called the Attentional Network Task (ANT), and no differences in GMV for selected ROIs between groups. However, chronological age predicted the size of interference and conflict effects for monolingual speakers only. We also observed a more widespread pattern of bilateral aging-effcts in brain regions that are classically associated with aging in monolingual speakers compared to bilingual speakers. Notably, GMV in the dorsal anterior cingulate cortex (dACC) and the level of daily exposure to a second language (L2) independently predict performance on the ANT in bilingual speakers. We conclude that regular (daily) bilingual experience mitigates the typical effects of aging on cognitive control at the behavioral and the neural level.
Neural basis of language switching and the cognitive models of bilingualism remain controversial. We explored the functional neuroanatomy of language switching implementing a new multimodal protocol assessing neuropsychological, functional magnetic resonance and intraoperative electrical stimulation mapping results.
A prospective series of 9 Spanish–Catalan bilingual candidates for awake brain surgery underwent a specific language switching paradigm implemented both before and after surgery, throughout the electrical stimulation procedure and during functional magnetic resonance both pre- and postoperatively. All patients were harboring left-hemispheric intrinsic brain lesions and were presenting functional language-related activations within the affected hemisphere.
Language functional maps were reconstructed on the basis of the intraoperative electrical stimulation results and compared to the functional magnetic resonance findings. Single language-naming sites (Spanish and Catalan), as well as language switching naming sites were detected by electrical stimulation mapping in 8 patients (in one patient only Spanish related sites were detected). Single naming points outnumbered the switching points and did not overlap with each other. Within the frontal lobe, the single language naming sites were found significantly more frequently within the inferior frontal gyrus as compared to the middle frontal gyrus [X² (1) = 20.3, p < .001]. Contrarily, switching naming sites were distributed across the middle frontal gyrus significantly more often than within the inferior frontal gyrus [X² (1) = 4.1, p = .043]. Notably, there was not always an overlap between functional magnetic resonance and electrical stimulation mapping findings. After surgery, patients did not report involuntary language switching and their neuropsychological scores did not differ significantly from the pre-surgical examinations. Our results suggest a functional division of the frontal cortex between naming and language switching functions, supporting that non-language specific cognitive control prefrontal regions (middle frontal gyrus) are essential to maintain an effective communication together with the classical language-related sites (inferior frontal gyrus).
The present study investigated the neural correlates of naming disadvantage of the dominant language under the mixed language context. Twenty one unbalanced Chinese-English bilinguals completed a cued picture naming task while being scanned with functional magnetic resonance imaging (fMRI). Behavioral results showed that naming pictures in the second lanuage (L2) was significantly slower than naming pictures in the first language (L1) under a single language context. When comparing picture naming in L2 to naming in L1, enhanced activity in the left inferior parietal lobule and left cerebellum was observed. On the contrary, naming pictures in Chinese (L1) was significantly slower than naming in English (L2) under the mixed language context. The fMRI results showed that bilateral inferior frontal gyri, right middle frontal gyrus, and right supplementary motor area were activated to a greater extent in L1 than in L2. These results suggest that the dominant language is inhibited to a greater extent to ensure the production of the second language under the mixed language context. Therefore, more attentional control resources are recruited when bilinguals produced the dominant language. The present study, for the first time, reveals neural correlates of L1 naming disadvantage under the mixed language context.