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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.
... Posterior and subcortical areas (mainly basal ganglia) seem to be more activated during language maintenance and selection (Abutalebi & Green, 2016;Calabria et al., 2018;Sulpizio et al., 2020). ...
... For MCI and AD, the neural hallmark is the entorhinal cortex and hippocampus that lead to long-term memory deficits as a first cognitive symptom, but also for executive control (Talwar et al., 2021). Therefore, as these neurodegenerative conditions affect different brain networks, we can expect distinct language control deficits based on the neural architecture of bilingual language control Calabria et al., 2018;. ...
The aim of the study is to explore the differential effects of neurodegenerative disorders on cross-language interference and facilitation, by comparing the performance in a bilingual Stroop task of Catalan–Spanish bilinguals with different neurodegenerative disorders [Mild Cognitive Impairment (MCI), n = 16; Alzheimer's disease (AD), n = 16; and Parkinson's disease (PD), n = 16)] and healthy controls (n = 14). Interference is the difference in naming latencies between the incongruent (colour words not matching with their ink colour) and control (non-colour words) conditions. Facilitation is the difference between the control and congruent conditions (colour words matching with their ink colour).
The results showed that AD and MCI patients, but not PD, showed a larger interference effect than healthy controls. Nevertheless, the patient groups showed the same facilitation effect as healthy controls.
The contribution of cortical and subcortical brain areas to cross-language interference suppression is discussed in relation to the type of brain degeneration.
... Across PA and MA tasks, bilinguals generally showed stronger right IPL/SMG activation, especially in the parietal regions as can be seen in Figure 2. The right IPL has been previously shown to support attention and selective inhibition demands during task-switching protocols (Singh-Curry & Husain, 2009). Prior research finding stronger right IPL activation in bilinguals has attributed this effect to the attentional aspects of dual language use (Calabria et al., 2018). Therefore, one possible explanation for our findings is that the right parietal regions help support various attention demands for dual language use because bilinguals are often found to co-activate both of their languages even when using only one of their languages (Arredondo et al., 2019). ...
Over the course of literacy development, children learn to recognize word sounds and meanings in print. Yet, they do so differently across alphabetic and character-based orthographies such as English and Chinese. To uncover cross-linguistic influences on children's literacy, we asked young Chinese-English simultaneous bilinguals and English monolinguals (N = 119, ages 5-10) to complete phonological and morphological awareness (MA) literacy tasks. Children completed the tasks in the auditory modality in each of their languages during functional near-infrared spectroscopy neuroimaging. Cross-linguistically, comparisons between bilinguals' two languages revealed that the task that was more central to reading in a given orthography, such as phonological awareness (PA) in English and MA in Chinese, elicited less activation in the left inferior frontal and parietal regions. Group comparisons between bilinguals and monolinguals in English, their shared language of academic instruction, revealed that the left inferior frontal was less active during phonology but more active during morphology in bilinguals relative to monolinguals. MA skills are generally considered to have greater language specificity than PA skills. Bilingual literacy training in a skill that is maximally similar across languages , such as PA, may therefore yield greater automaticity for this skill, as reflected in the lower activation in bilinguals relative to monolinguals. This interpretation is supported by negative correlations between proficiency and brain activation. Together, these findings suggest that both the structural characteristics and literacy experiences with a given language can exert specific influences on bilingual and monolingual chil-dren's emerging brain networks for learning to read. K E Y W O R D S bilingual, cross-linguistic, fNIRS, morphological awareness, phonological awareness
... Further, bilingual patients with aphasia may exhibit pathological code-switching or code-mixing (Fabbro et al., 2000), thought to be caused by an impairment of "bilingual language control" (BLC). BLC refers to the ability to avoid interference of the two languages, and to select one language over the other depending on the communicative context (Calabria et al., 2018). Neurobiologically, bilinguals are thought to differ from monolinguals in the sense that their linguistic functions are effectuated by similar neural circuits as in monolinguals, but with an increased demand on executive and attention control processes (Abutalebi, 2008). ...
Transcranial Direct Current Stimulation may be a useful neuromodulation tool for enhancing the effects of speech and language therapy in people with aphasia, but research so far has focused on monolinguals. We present the effects of 9 sessions of anodal cerebellar tDCS (ctDCS) coupled with language therapy in a bilingual patient with chronic post-stroke aphasia caused by left frontal ischemia, in a double-blind, sham-controlled within-subject design. Language therapy was provided in his second language (L2). Both sham and anodal treatment improved trained picture naming in the treated language (L2), while anodal ctDCS in addition improved picture naming of untrained items in L2 and his first language, L1. Picture description improved in L2 and L1 after anodal ctDCS, but not after sham.
... Cognitive consequences associated with bilinguals' need to coordinate the use of multiple languages became the focus of a considerable amount of additional research, eventually forming the basis for the (now) most widely-cited idea in bilingual language control: the adaptive control hypothesis (ACH; Green and Abutalebi, 2013). At its core, the ACH assumes that language experience is a cognitive process that can modify the structure and function of the brain (Abutalebi and Green, 2007;Calabria et al., 2018;Tao et al., 2021). As both languages of a bilingual are simultaneously active (Abutalebi and Green, 2007;Costa et al., 2006;Hermans et al., 1998;Kroll et al., 2012), some underlying inhibitory process must be recruited in support of successful communication. ...
Whether bilingualism results in improved executive function is controversial. According to some researchers, putative bilingual advantages can be explained by individual differences in unmeasured non-linguistic variables. Additionally, commonly used models containing exclusively fixed-effects do not account for the data structure inherent in multi-trial behavioral tasks. Mixed-effects models by contrast address both of these issues, allowing for a more valid test of the bilingual advantage hypothesis. The present study aimed to assess whether the choice of analysis method impacted on results when investigating the bilingual advantage in executive function. Simon task data from Mandarin-English speaking Chinese adolescents were analyzed using separate fixed and mixed-effects models. Comparisons between models revealed considerable differences in the pattern of results. Most notable was the observation that a number of previously significant main effects on task performance were no longer significant in a mixed model accounting for the inclusion of multiple trials for each participant. Implications for the bilingual advantage are discussed.
Professor Albert Costa (1972-2018) was one of the most influential scholars in the fields of psycholinguistics and bilingualism. This book provides a faithful look at the most relevant lines of research in which he worked during his academic career. Written by some of his close collaborators and friends, the book presents a coherent summary of the most relevant psycholinguistic theories on language processing and bilingualism, including critical reviews to current models of lexical access, the representation of cognate words, neurolinguistic models of bilingualism, cross-linguistic effects in bimodal bilinguals (sign language), prediction processes and linguistic alignment in bilinguals, the influence of foreign-language effects in social cognition and the effects of bilingualism in emotion and decision making processing. This volume is a tribute to Prof. Costa and his work, and is born from a deep love and respect for his way of approaching the science of multilingualism from a psycholinguistic perspective.
The field of neuropsychology can contribute to bilingualism research from a multidisciplinary perspective that ranges from psycholinguistics and brain imaging studies. While the psycholinguistic approach provides the outlook on linguistic processes in experimental study of patients with brain damage, neural models define the underlying brain areas of such processes and help to predict language deficits in said patients. Current neural models of bilingualism do not provide accurate predictions of deficits in bilinguals with brain damage since they have not been tested in a systematic way. However, they do offer a roadmap for the underlying cognitive and linguistic processes of bilingual language control and speech production. In this chapter, I propose how a neurolinguistic approach to bilingualism might be implemented in neuropsychology by including: (a) the application of traditional methods of cognitive (neuro)psychology to the field of bilingualism, such as dissociations, (b) the use of psycholinguistic methods, and (c) how neurodegenerative diseases may be a neuropsychological paradigm in which one can study bilingual language processes.
Alzheimer’s disease (AD) is an age-related neurocognitive disorder that is epidemic in the elderly population. Currently, there are limited pharmacological interventions, and this has heightened the urgency to identify potential preventable or modifiable risk factors that promote resilience to the neuropathological effects of AD. The regular use of two or more languages is one such factor that may increases cognitive reserve through the long-standing executive control involved in managing multiple languages in the brain. There is also evidence that bilingualism is associated with increased brain reserve or maintenance, particularly in frontal-executive structures and networks. This review examines the current, sometimes conflicting literature on bi/multilingualism and AD. These studies have confounding variations in the assessment of age of second language onset, language proficiency, language usage, and whether determining incidence of AD or age of symptom onset. Despite these limitations, most publications support the presence of increased frontal-executive reserve that compensates for the development of AD neuropathology and, thereby, delays the emergence of clinical symptoms of dementia by about 4-5 years. Although regularly speaking more than one language does not protect against AD neuropathology, the delay in its clinical expression has a potentially significant impact on the lifelong morbidity from this age-related disease. Learning other languages may be an important modifiable factor for delaying the clinical expression of AD in later life.
Humans engage multiple brain systems to read successfully, including using regions important for vision, language, and control. Control refers to the set of executive processes in the brain that guide moment‐to‐moment behavior in service of our goals. There is a growing appreciation for the role of the brain's control system in reading comprehension, in reading skill change over time, and in those who have difficulty with the reading process. One way to understand the brain's control engagement in reading may be to study control engagement across multiple tasks in order to study consistencies, or cross‐task similarities, relative to reading‐specific variations. In this commentary, I briefly summarize some of our recent work studying the brain's control networks across different tasks (e.g., when reading, or doing different executive function tasks). I then review our findings of when control activation does or does not relate to measures of reading ability, and reading growth over time. The utility of cross‐task comparisons in neuroimaging is noted, as well as the need to better understand multiple sources of heterogeneity in our developmental samples. I end by discussing a few of the many future directions for further study of the brain with regard to the brain's control processing and academic achievement.
Bilingualism is a ubiquitous global phenomenon. Beyond being a language experience, bilingualism also entails a social experience, and it interacts with development and learning, with cognitive and neural consequences across the lifespan. The authors of this volume are world renowned experts across several subdisciplines including linguistics, developmental psychology, and cognitive neuroscience. They bring to light bilingualism’s cognitive, developmental, and neural consequences in children, young adults, and older adults. This book honors Ellen Bialystok, and highlights her profound impact on the field of bilingualism research as a lifelong experience. The chapters are organized into four sections: The first section explores the complexity of the bilingual experience beyond the common characterization of “speaking multiple languages.” The next section showcases Ellen Bialystok’s earlier impact on psychology and education; here the contributors answer the question “how does being bilingual shape children’s development?” The third section explores cognitive and neuroscientific theories describing how language experience modulates cognition, behavior, and brain structures and functions. The final section shifts the focus to the impact of bilingualism on healthy and abnormal aging and asks whether being bilingual can stave off the effects of dementia by conferring a “cognitive reserve.”
Bilingualism is a ubiquitous global phenomenon. Beyond being a language experience, bilingualism also entails a social experience, and it interacts with development and learning, with cognitive and neural consequences across the lifespan. The authors of this volume are world renowned experts across several subdisciplines including linguistics, developmental psychology, and cognitive neuroscience. They bring to light bilingualism’s cognitive, developmental, and neural consequences in children, young adults, and older adults. This book honors Ellen Bialystok, and highlights her profound impact on the field of bilingualism research as a lifelong experience. The chapters are organized into four sections: The first section explores the complexity of the bilingual experience beyond the common characterization of “speaking multiple languages.” The next section showcases Ellen Bialystok’s earlier impact on psychology and education; here the contributors answer the question “how does being bilingual shape children’s development?” The third section explores cognitive and neuroscientific theories describing how language experience modulates cognition, behavior, and brain structures and functions. The final section shifts the focus to the impact of bilingualism on healthy and abnormal aging and asks whether being bilingual can stave off the effects of dementia by conferring a “cognitive reserve.”
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.
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.
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.
