Neural signatures of inhibitory control in bilingual spoken production

Transcranial magnetic stimulation of the right inferior frontal gyrus impairs bilinguals' performance in language-switching tasks

It is widely accepted that bilinguals activate both languages simultaneously, even when intending to speak only one. A prevailing theory proposes that bilinguals inhibit the nontarget language to produce the target language, thought to be supported by evidence that the right inferior frontal gyrus (rIFG), a region typically associated with inhibition, is activated during language-switching tasks. However, it remains unclear whether the rIFG plays a causal or epiphenomenal role in this process. To explore the role of the rIFG, the present study employed transcranial magnetic stimulation (TMS) to modulate its neural activity and evaluate subsequent behavior in bilinguals. Specifically, twenty-nine Chinese-English bilinguals participated in the study and performed picture-naming tasks in single- and dual-language contexts after receiving sham stimulation (Sham), continuous theta burst stimulation (cTBS), or intermittent theta burst stimulation (iTBS) over the rIFG in three separate visits. Sham served as a control, with cTBS and iTBS intended to decrease and increase cortical excitability, respectively. We found that, compared to Sham, cTBS led to larger asymmetric switching costs and smaller asymmetric mixing costs, whereas iTBS resulted only in smaller asymmetric mixing costs. These findings suggest that cTBS targeting the rIFG likely impairs both local and global control. However, iTBS applied to the rIFG alone may not necessarily enhance language control mechanisms and could even hinder global control. Moreover, exploratory analyses found pronounced TMS-induced impairments in less balanced bilinguals, implying their potentially greater reliance on bilingual language control. Overall, this study is the first to suggest a causal role of the rIFG in language switching.

Tracking Components of Bilingual Language Control in Speech Production: An fMRI Study Using Functional Localizers

When bilingual speakers switch back to speaking in their native language (L1) after having used their second language (L2), they often experience difficulty in retrieving words in their L1. This phenomenon is referred to as the L2 after-effect. We used the L2 after-effect as a lens to explore the neural bases of bilingual language control mechanisms. Our goal was twofold: first, to explore whether bilingual language control draws on domain-general or language-specific mechanisms; second, to investigate the precise mechanism(s) that drive the L2 after-effect. We used a precision fMRI approach based on functional localizers to measure the extent to which the brain activity that reflects the L2 after-effect overlaps with the language network (Fedorenko et al., 2010) and the domain-general multiple demand network (Duncan, 2010), as well as three task-specific networks that tap into interference resolution, lexical retrieval, and articulation. Forty-two Polish-English bilinguals participated in the study. Our results show that the L2 after-effect reflects increased engagement of domain-general but not language-specific resources. Furthermore, contrary to previously proposed interpretations, we did not find evidence that the effect reflects increased difficulty related to lexical access, articulation, and the resolution of lexical interference. We propose that difficulty of speech production in the picture naming paradigm-manifested as the L2 after-effect-reflects interference at a nonlinguistic level of task schemas or a general increase of cognitive control engagement during speech production in L1 after L2.

Domain-general and language-specific contributions to speech production in a second language: an fMRI study using functional localizers

For bilinguals, speaking in a second language (L2) compared to the native language (L1) is usually more difficult. In this study we asked whether the difficulty in L2 production reflects increased demands imposed on domain-general or core language mechanisms. We compared the brain response to speech production in L1 and L2 within two functionally-defined networks in the brain: the Multiple Demand (MD) network and the language network. We found that speech production in L2 was linked to a widespread increase of brain activity in the domain-general MD network. The language network did not show a similarly robust differences in processing speech in the two languages, however, we found increased response to L2 production in the language-specific portion of the left inferior frontal gyrus (IFG). To further explore our results, we have looked at domain-general and language-specific response within the brain structures postulated to form a Bilingual Language Control (BLC) network. Within this network, we found a robust increase in response to L2 in the domain-general, but also in some language-specific voxels including in the left IFG. Our findings show that L2 production strongly engages domain-general mechanisms, but only affects language sensitive portions of the left IFG. These results put constraints on the current model of bilingual language control by precisely disentangling the domain-general and language-specific contributions to the difficulty in speech production in L2.

Multilingual Language Diversity Protects Native Language Production under Different Control Demands

The use of multiple languages has been found to influence individuals' cognitive abilities. Although some studies have also investigated the effect of multilingualism on non-native language proficiency, fewer studies have focused on how multilingual experience affects native language production. This study investigated the effect of multilingualism on native language production, specifically examining control demands through a semantic Go/No-Go picture naming task. The multilingual experience was quantified using language entropy, which measures the uncertainty and diversity of language use. Control demands were achieved by manipulating the proportion of Go (i.e., naming) trials in different conditions. Results showed that as control demands increased, multilingual individuals exhibited poorer behavioral performance and greater brain activation throughout the brain. Moreover, more diverse language use was associated with higher accuracy in naming and more interconnected brain networks with greater involvement of domain-general neural resources and less domain-specific neural resources. Notably, the varied and balanced use of multiple languages enabled multilingual individuals to respond more efficiently to increased task demands during native language production.

The temporal dynamics of bilingual language control

Bilinguals need to control interference from the nontarget language, to avoid saying words in the wrong language. This study investigates how often bilinguals apply such control in a dual-language mode, when speaking one language after the other when the two languages cannot be used interchangeably: over and over (every time they say a word), or only once (the first time they use a word or language after a language switch). Three groups of Spanish-English bilinguals named pictures first in their dominant, then in their nondominant, and then again in their dominant language; a fourth control group of bilinguals named pictures in their dominant language throughout. The study targeted language control aftereffects on the dominant language after nondominant naming, typically assumed to reflect recovery from previously applied inhibition. If the dominant language is inhibited every time a nondominant word is produced, subsequent dominant-language naming latencies should increase in proportion to the number of pictures previously named in the nondominant language. We found, however, that the number of nondominant picture-naming trials did not affect subsequent naming latencies in the dominant language, despite ample statistical power to detect such effects if they existed. The results suggest that, in a dual-language mode, bilingual (inhibitory) control is applied over a word's translation upon the word's first mention but not over and over with subsequent repetitions. This conclusion holds true equally for inhibitory and non-inhibitory language control mechanisms.

Noun-phrase production as a window to language selection: An ERP study

Characterising the time course of non-native language production is critical in understanding the mechanisms behind successful communication. Yet, little is known about the modulating role of cross-linguistic influence (CLI) on the temporal unfolding of non-native production and the locus of target language selection. In this study, we explored CLI effects on non-native noun phrase production with behavioural and neural methods. We were particularly interested in the modulation of the P300 as an index for inhibitory control, and the N400 as an index for co-activation and CLI. German late learners of Spanish overtly named pictures while their EEG was monitored. Our results indicate traceable CLI effects at the behavioural and neural level in both early and late production stages. This suggests that speakers faced competition between the target and non-target language until advanced production stages. Our findings add important behavioural and neural evidence to the underpinnings of non-native production processes, in particular for late learners.

Similar activation patterns in the bilateral dorsal inferior frontal gyrus for monolingual and bilingual contexts in second language production

Language production is a vital process of communication. Although many studies have devoted to the neural mechanisms of language production in bilinguals, they mainly focused on the mechanisms of cognitive control during language switching. Therefore, it is not clear how naming context influences the neural representations of linguistic information during language production in bilinguals. To address that question, the present study adopted representational similarity analysis (RSA) to investigate the neural pattern similarity (PS) between the monolingual and bilingual contexts separately for native and second languages. Consistent with previous findings, bilinguals behaviorally performed worse, and showed greater activation in brain regions for cognitive control including the anterior cingulate cortex and dorsolateral prefrontal cortex in the bilingual context relative to the monolingual context. More importantly, RSA revealed that bilinguals exhibited similar neural activation patterns in the bilateral dorsal inferior frontal gyrus between the monolingual and bilingual contexts in the production of the second language. Moreover, higher cross-context PS in the right inferior frontal gyrus was associated with smaller differences in naming speed of second language between the monolingual and bilingual contexts. These results suggest that similar linguistic representations are encoded for the monolingual and bilingual contexts in the production of non-dominant language.

Neural signatures of inhibitory control in intra-sentential code-switching: Evidence from fMRI

In this study we examined the neural control mechanisms that are at play when habitual code-switchers read code-switches embedded in a sentence context. The goal was also to understand if and to what extent the putative control network that is engaged during the comprehension of code-switched sentences is modulated by the linguistic regularity of those switches. Towards that goal, we tested two different types of code switches (switches at the noun-phrase boundary and switches at the verb-phrase boundary) that despite being both represented in naturalistic corpora of code switching, show different distributional properties. Results show that areas involved in general cognitive control (e.g., pre-SMA, anterior cingulate cortex) are recruited when processing code-switched sentences, relative to non-code-switched sentences. Additionally, significant activation in the cerebellum when processing sentences containing code-switches at the noun-phrase boundary suggests that habitual code-switchers might engage a wider control network to adapt inhibitory control processes according to task demands. Results are discussed in the context of the current literature on neural models of bilingual language control.

Patterns and networks of language control in bilingual language production

Many studies have examined the cognitive and neural mechanisms of bilingual language control, but few of them have captured the pattern information of brain activation. However, language control is a functional combination of both cognitive control and language production which demonstrates distinct patterns of neural representations under different language contexts. The first aim of the present study was to explore the brain activation patterns of language control using multivoxel pattern analysis (MVPA). During the experiment, Chinese-English bilinguals were instructed to name pictures in either Chinese or English according to a visually presented cue while being scanned with functional magnetic resonance imaging (fMRI). We found that patterns of neural activity in frontal brain regions including the left dorsolateral prefrontal cortex, left inferior frontal gyrus, left supplementary motor area, anterior cingulate cortex, bilateral precentral gyri, and the left cerebellum reliably discriminated between switch and non-switch conditions. We then modeled causal interactions between these regions by applying effective connectivity analyses based on an extended unified structure equation model (euSEM). The results showed that frontal and fronto-cerebellar connectivity were key components of the language control network. These findings further reveal the engagement of the cognitive control network in bilingual language production.

Cognitive control in bilinguals: Proficiency and code-switching both matter

We examined the impact of bilingualism as a construct of both language usage and language proficiency on the effectiveness of cognitive control. In particular, we asked whether the frequency of daily dense code-switching - frequent change of language within and between sentences with the same interlocutor- and the level of L2 proficiency separately and or interactively affect cognitive control efficiency in the Simon task. Results from 134 bilinguals showed that frequently code-switching bilinguals had fewer errors and their accuracy rate improved over trials leading to a smaller Simon effect. For response times (RTs), however, L2 proficiency modulated the Simon effect, and interacted with code-switching frequency in intricate ways in modulating overall RTs over trials. Crucially, highly proficient frequently code-switching bilinguals were better at conflict adaptation. These results show that bilinguals differ among themselves, and that researchers need to take both proficiency and language use into account to test the impact of bilingual experience on cognitive control. Bilingualism should be regarded as a continuum, with many different factors contributing to the language experience and affecting cognitive functioning.

Native language inhibition predicts more successful second language learning: Evidence of two ERP pathways during learning

How some individuals succeed in learning a second language as adults is still an unsolved question in cognitive neuroscience. At the brain level, adults' electrophysiological responses to input in a second language may differ after completing different types of training. However, there is limited understanding of what neural pathways are activated as learning unfolds, and which patterns of activation lead to successful learning. Using brain event-related potentials, this study explored whether individual brain responses to practice difficulty during second language learning predict learning outcomes. English-speaking learners of Spanish practiced completing newly learned phrases in their second language. For some learners, all the choices presented during practice were "easy" because non-target choices were unrelated distractors. In the more "difficult" practice mode, however, learners had to avoid choosing a competing word that would be acceptable based on their native language, but not in the second language being learned. Performance during practice was similar in both groups of learners. Critically, divergence in event-related potentials indicated alternative strategies to practice, based on the level of difficulty. At the group level, learners completing the easier practice revealed increased monitoring when making responses; in the difficult condition, learners showed inhibition of their native language (i.e., an N400 for phrases congruent with the native language) to avoid interference during word selection. Individual brain responses indexing the degree of native language inhibition predicted learning rates in tests.

Bilingual Language Experience Shapes Resting-State Brain Rhythms

An increasing body of research has investigated how bilingual language experience changes brain structure and function, including changes to task-free, or "resting-state" brain connectivity. Such findings provide important evidence about how the brain continues to be shaped by different language experiences throughout the lifespan. The neural effects of bilingual language experience can provide evidence about the additional processing demands placed on the linguistic and/or executive systems by dual-language use. While considerable research has used MRI to examine where these changes occur, such methods cannot reveal the temporal dynamics of functioning brain networks at rest. The current study used data from task-free EEGS to disentangle how the linguistic and cognitive demands of bilingual language use impact brain functioning. Data analyzed from 106 bilinguals and 91 monolinguals revealed that bilinguals had greater alpha power, and significantly greater and broader coherence in the alpha and beta frequency ranges than monolinguals. Follow-up analyses showed that higher alpha was related to language control: more second-language use, higher native-language proficiency, and earlier age of second-language acquisition. Bilateral beta power was related to native-language proficiency, whereas theta was related to native-language proficiency only in left-hemisphere electrodes. The results contribute to our understanding of how the linguistic and cognitive requirements of dual-language use shape intrinsic brain activity, and what the broader implications for information processing may be.

Neuro-dynamics of executive control in bilingual language switching: An MEG study

Bilinguals have a remarkable ability to juggle two languages. A central question in the field is concerned with the control mechanisms that enable bilinguals to switch language with ease. Theoretical models and neuroimaging evidence suggest that a range of control processes are at play during language switching, and their underlying neural mechanisms are closely related to executive function. What remains unclear is when these control processes are engaged in language switching. In this study, we used magnetoencephalography (MEG) to examine the brain activity while unbalanced Mandarin-English bilinguals performed a digit-naming task with cued language switching. Following presentation of the language cue, an asymmetrical switch effect was observed in the left inferior frontal gyrus (IFG), where switch-related increase in evoked brain activity was larger for switching into the non-dominant language. Following presentation of the naming target, evoked brain activity in the right IFG was larger when naming was required in the non-dominant language compared to the dominant language. We conclude that control processes take place in two stages during language switching, with the left IFG resolving interference following cue presentation and the right IFG inhibiting competing labels following target presentation.

Are you really cursing? Neural processing of taboo words in native and foreign language

The use of socially opprobrious words (taboo words) is a cross-cultural phenomenon occurring between individuals from almost all social extractions. The neurocognitive correlates of using taboo words in the native language (L1) as compared to their use in a second (L2) language are largely unknown. We used fMRI to investigate the processing of taboo and non-taboo stimuli in monolinguals (Experiment 1) and highly proficient bilinguals (Experiment 2) engaged in lexical decision tasks. We report that for L1 socio-pragmatic knowledge is automatically conveyed and taboo words are processed with less effort than non-taboo words. For L2 the processing of taboo words is more effortful and engages additional structures (anterior cingulate cortex, insula) involved in social-norm representation and evaluation. Our results contribute to understand the interface between language and social-norm processing indicating that lexical processing is affected by socio-pragmatic knowledge, but only when the speaker has a contextual use of the language.