Subcortical structures implicated in language control and processing adapt structurally with increasing language experience. However, the adaptation patterns across different subcortical structures remain unclear. Previous findings from bilinguals and multilinguals reveal renormalisation patterns, lending support to the Dynamic Restructuring Model (Pliatsikas, 2020). These patterns are composed of increasing volumes during the initial stages of language learning, and subsequent reductions as experience increases. T1-weighted images from 14 English monolinguals, 14 bilinguals, 14 trilinguals, and 14 quadrilinguals were obtained. The volumes of five subcortical regions implicated in language control and processing were compared amongst the groups. The findings showed group differences for every structure – caudate nucleus, nucleus accumbens, putamen, globus pallidus and thalamus. Complex patterns were unveiled for each structure, suggesting expansions and renormalisations that differ in trajectory for each group. These findings highlight the dynamic progression of subcortical adaptations, and support the notion of structural renormalisation as language experience grows.

Previous research suggests that bilingual language control requires domain-general cognitive control. Recent research suggests that exploration of individual differences is key for understanding the relationship between bilingual language control and cognitive control. The current study used multi-voxel pattern analysis (MVPA) to examine within-subject patterns of fMRI activity in the dorsolateral prefrontal cortex (DLPFC) during bilingual language switching and non-linguistic task-switching. We hypothesized that bilinguals would have identifiable, within-subject patterns of DLPFC activity for both types of switching and that bilinguals and monolinguals would differ in patterns of DLPFC activity for task-switching. We were unable to identify patterns of DLPFC activity associated with bilingual language switching. Task-switching was related to patterns of left DLPFC activity for both bilinguals and monolinguals, and there were identifiable patterns of right DLPFC activity for the bilinguals only. These findings suggest that the DLPFC is not the key brain structure connecting bilingual language and task-switching.

To better explain various neurocognitive consequences of bilingualism, recent investigations have adopted continuous measures of bilingual experience, as opposed to binary bi/monolingual distinctions. However, few studies have considered whether bilingualism's effects on cognition are modulated by the linguistic distance (LD) between L1 and L2, and none of the existing studies has examined cognitive consequences of LD in aging populations. Here, we investigated the modulatory role of LD on the relationship between bilingualism, executive performance, and cognitive reserve (CR) in a sample of senior bilinguals. Our results show a dynamic trajectory of LD effects, with more distant language pairs exerting maximum effects at initial stages of bilingual experience – and closer language pairs at advanced stages. Bilingualism-related CR effects emerged only in the individuals with closer language pairs, suggesting that the language control stage of bilingual experience may play a key role in CR accrual, as compared to the L2 learning stage.

Bilingualism is thought to confer advantages in executive functioning, thereby contributing to cognitive reserve and a later age of dementia symptom onset. While the relation between bilingualism and age of onset has been explored in Alzheimer's dementia, there are few studies examining bilingualism as a contributor to cognitive reserve in frontotemporal dementia (FTD). In line with previous findings, we hypothesized that bilinguals with behavioral variant FTD would be older at symptom onset compared to monolinguals, but that no such effect would be found in patients with nonfluent/agrammatic variant primary progressive aphasia (PPA) or semantic variant PPA. Contrary to our hypothesis, we found no significant difference in age at symptom onset between monolingual and bilingual speakers within any of the FTD variants, and there were no notable differences on neuropsychological measures. Overall, our results do not support a protective effect of bilingualism in patients with FTD-spectrum disease in a U.S. based cohort.

Studies investigating the role of dual language use in modulating executive functions have reported mixed results, with some studies reporting benefits in older adults. These studies typically focus on bilingual settings, while the role of dual language use in diglossic settings is rarely investigated. In diglossia, the two language varieties are separated by context, making it an ideal test case for the effects on cognition of Single Language Contexts, as defined by the Adaptive Control Hypothesis (Green & Abutalebi, 2013). We compare the performances of three groups of older adults, Arab diglossics (n = 28), bilinguals (n = 29), and monolinguals (n = 41), on the Flanker and Stroop tasks, measuring inhibition abilities, and the Color-shape task, measuring switching abilities. We report a diglossic benefit in inhibition as measured by the Flanker task only, and no benefits for the bilingual group. These findings are discussed with reference to conversational contexts in dual language use.

The study of the brains’ oscillatory activity has been a standard technique to gain insights into human neurocognition for a relatively long time. However, as a complementary analysis to ERPs, only very recently has it been utilized to study bilingualism and its neural underpinnings. Here, we provide a theoretical and methodological starter for scientists in the (psycho)linguistics and neurocognition of bilingualism field(s) to understand the bases and applications of this analytical tool. Towards this goal, we provide a description of the characteristics of the human neural (and its oscillatory) signal, followed by an in-depth description of various types of EEG oscillatory analyses, supplemented by figures and relevant examples. We then utilize the scant, yet emergent, literature on neural oscillations and bilingualism to highlight the potential of how analyzing neural oscillations can advance our understanding of the (psycho)linguistic and neurocognitive understanding of bilingualism.

An event-related potential (ERP) study was conducted to evaluate the efficacy of two learning methods for the acquisition of vocabulary in a foreign language (FL). In the semantic method, FL words were presented with pictures denoting their meaning and the learners practiced with a semantic categorization task (to indicate whether FL words were exemplars of a semantic category). In the lexical method, FL words were paired with their translation in the first language (L1) and the learners practiced with a letter-monitoring task (to indicate whether L1-FL words contained a grapheme). A translation task and a picture-naming task were used to evaluate FL acquisition. ERP modulations associated with semantic processing were more evident and broadly distributed in the semantic versus lexical learning group. The pattern of results suggests that a single session of semantic learning favors the establishment of connections between semantics and the words learned in a new language.

Much research has been dedicated to the effects of bilingualism on executive control (EC). For bilinguals with aphasia, the interplay with EC is complex. In this systematic review, we synthesize research on this topic and provide an overview of the current state of the field. First, we examine the evidence for EC deficits in bilingual persons with aphasia (bPWA). We then discuss the domain generality of bilingual language control impairments. Finally, we evaluate the bilingual advantage hypothesis in bPWA. We conclude that (1) EC impairments in bPWA are frequently observed, (2) experimental results on the relationship between linguistic and domain-general control are mixed, (3) bPWA with language control problems in everyday communication have domain-general EC problems, and (4) there are indications for EC advantages in bPWA. We end with directions for experimental work that could provide better insight into the intricate relationship between EC and bilingual aphasia.

Dual/multiple language use has been shown to affect cognition and its neural substrate, although the replicability of such findings varies, partially due to neglecting the role of interindividual variability in bilingual experience. To address this, we operationalized the main bilingual experience factors as continuous variables, investigating their effects on executive control performance and neural substrate deploying a Flanker task and structural magnetic resonance imaging. First, higher L2 proficiency predicted better executive performance. Second, neuroimaging results indicated that bilingualism-related neuroplasticity may peak at a certain stage of bilingual experience and eventually revert, possibly following functional specialization. Importantly, experienced bilinguals optimized behavioral performance independently of volumetric variations, suggesting a degree of performance gain even with lower GMV. Hence, the effects of bilingualism on cognition may evolve with experience, with improvements in functional efficiency eventually replacing structural changes. We conclude that individual differences in bilingual experience modulate cognitive and neural consequences of bilingualism.

Numerous studies have argued that bilingualism has effects on cognitive functions. Recently, in light of increasingly mixed empirical results, this claim has been challenged. One might ponder if there is enough evidence to justify a cessation to future research on the topic or, alternatively, how the field could proceed to better understand the phantom-like appearance of bilingual effects. Herein, we attempt to frame this appearance at the crossroads of several factors such as the heterogeneity of the term ‘bilingual’, sample size effects, task effects, and the complex dynamics between an early publication bias that favours positive results and the subsequent Proteus phenomenon. We conclude that any definitive claim on the topic is premature and that research must continue, albeit in a modified way. To this effect, we offer a path forward for future multi-lab work that should provide clearer answers to whether bilingualism has neurocognitive effects, and if so, under what conditions.

Previous research examining whether bilinguals exhibit enhanced working memory (WM) compared to monolinguals has yielded mixed results. This inconsistency may be due to lack of sensitivity in behavioral and neuropsychological measures. The current study aimed to investigate the effects of bilingualism on WM by focusing on brain activity patterns (event-related potentials) in monolinguals and bilinguals during a WM task. We recorded brain activity while participants (26 monolingual English speakers and 28 English–French bilinguals) performed a delayed matching-to-sample task. Although performance measures were similar, electrophysiological differences were present across groups. Bilinguals exhibited larger P3b amplitudes than monolinguals, and smaller negative slow wave and N2b amplitudes during retrieval. These results suggest that bilinguals may have more cognitive resources available in WM to allocate to task completion, and that task completion may be less effortful for bilinguals than for monolinguals.

Simultaneous interpreting is a complex cognitive task that requires the concurrent execution of multiple processes: listening, comprehension, conversion of a message from one language to another, speech production, and self-monitoring. This requires the deployment of an array of linguistic and cognitive control mechanisms that must coordinate the various brain systems implicated in handling these tasks. How the brain handles this challenge remains an open question, and recent brain imaging investigations have begun to complement the theories based on behavioural data. fMRI studies have shown that simultaneous interpreting engages a network of brain regions encompassing those implicated in speech perception and production, language switching, self-monitoring, and selection. Structural imaging studies have been carried out that also indicate modifications to a similar set of structures. In the present paper, we review the extant data and propose an integrative model of simultaneous interpreting that piggybacks on existing theories of multilingual language control.

We examine whether early acquisition of a second language (L2) leads to native-like neural processing of phonemic contrasts that are absent in the L1. Four groups (adult and child monolingual speakers of English; adult and child early bilingual speakers of English and Spanish, exposed to both languages before 5 years of age) participated in a study comparing the English /ɪ/ - /ε/ contrast. Neural measures of automatic change detection (Mismatch Negativity, MMN) and attention (Processing Negativity, PN and Late Negativity, LN) were measured by varying whether participants tracked the stimulus stream or not. We observed no effect of bilingualism on the MMN, but adult bilinguals differed significantly from adult monolinguals on neural indices of attention. The child bilinguals were indistinguishable from their monolingual peers. This suggest that learning a L2 before five years of age leads to native-like phoneme discrimination, but bilinguals develop increased attentional sensitivity to speech sounds.

Bilingualism has been said to improve cognition and even delay the onset of Alzheimer's disease (AD). This research aimed to investigate whether bilingualism leaves a neurophysiological trace even when people are highly educated. We expected bilinguals to present better preserved brain functional networks, which could be a trace of higher cognitive reserve. With this purpose, we conducted a magnetoencephalographic study with a group of healthy older adults. We estimated functional connectivity using phase-locking value and found five clusters in parieto-occipital regions in which bilinguals exhibited greater functional connectivity than monolinguals. These clusters included brain regions typically implicated in language processing. Furthermore, these functional changes correlated with caudate volumes (a key region in language shifting and control) in the bilingual sample. Interestingly, decreased Functional Connectivity between posterior brain regions had already been identified as an indicator of aging/preclinical AD but, according to our study, bilingualism seems to exert the opposite effect.

Research on the effects of bi- and multi-lingualism on brain structure has so far yielded variable patterns. Although it cannot be disputed that learning and using additional languages restructures grey (cortical, subcortical and cerebellar) and white matter in the brain, both increases and reductions in regional volume and diffusivity have been reported. This paper revisits the available evidence from simultaneous and sequential bilinguals, multilinguals, interpreters, bimodal bilinguals, children, patients and healthy older adults from the perspective of experience-based neuroplasticity. The Dynamic Restructuring Model (DRM) is then presented: a three-stage model accounting for, and reinterpreting, all the available evidence by proposing a time-course for the reported structural adaptations, and by suggesting that these adaptations are dynamic and depend on the quantity and quality of the language learning and switching experience. This is followed by suggestions for future directions for the emerging field of bilingualism-induced neuroplasticity.

In bilinguals, language proficiency has been advanced to influence the involvement of domain-general control networks in language selection. We assessed, in university student translators with moderate- to high-second language (L2) proficiency depending on their translation educational level, the functional activity in the key language and control areas (the caudate nucleus, anterior cingulate, and prefrontal cortex), during task- and language-selection in an oral production context. We found that L2 proficiency influenced the relative involvement of our regions of interest during language selection vs domain-general cognitive control processes. While the left middle frontal and left caudate areas were more involved during linguistic than alphanumeric task selection in the low L2 proficiency group, these regions were similarly involved in both tasks in the high-L2 proficiency group. These findings suggest that language selection relies primarily on a network within domain-general cognitive control system with an increase in resource needs when L2 proficiency is low.

Language acquisition is characterized by progressive use of inflectional morphology marking verb tense and agreement. Linguistic milestones are also linked to left-brain lateralization for language specialization. We used neuroimaging (fNIRS) to investigate how bilingual exposure influences children's cortical organization for processing morpho-syntax. In Study 1, monolinguals and bilinguals (n = 39) completed a grammaticality judgment task that included English sentences with violations in earlier-acquired (verb agreement) and later-acquired (verb tense/agreement) structures. Groups showed similar performance and greater activation in left inferior frontal region (IFG) for later- than earlier-acquired conditions. Bilinguals showed stronger and more restricted left IFG activation. In Study 2, bilinguals completed a comparable Spanish task revealing patterns of left IFG activation similar to English. Taken together, the findings suggest that bilinguals with linguistic competence at parity with monolingual counterparts have a higher degree of cortical specialization for language, likely a result of enriched linguistic experiences.

DTI is an established method to study cerebral white-matter microstructure. Two established measures of DTI are fractional anisotropy (FA) and mean diffusivity (MD) and both differ for bilingual and monolingual speakers. Less is known about differences in two other measures called radial (RD) and axial diffusivity (AD). We report differences in mean RD and AD-values in the right superior longitudinal fasciculus (SLF) and forceps minor between bilingual (Hindi–English) and monolingual (English) speakers as well as differences in mean FA-values in the anterior thalamic radiation, right inferior fronto-occipital and inferior longitudinal fasciculus (ILF) and mean MD-values in forceps minor and bilateral SLF. Noteworthy, a positive correlation between L2 proficiency and mean RD-values in the right SLF was observed. We suggest that changes in the geometry of white matter tracts reflect regular bilingual language experience and contend that neuroplasticity in right SLF results from demands on cognitive control for bilingual speakers.

Speaking a late-acquired second language (L2) involves increased cognitive demands, as has been shown mainly in young and middle-aged adults. To investigate grammatical inflection in older L2 speakers, we acquired behavioral and functional magnetic resonance imaging data, while L1 and L2 speakers performed a grammaticality judgment task. L2 speakers showed higher error rates than native speakers, specifically when incorrect forms had to be rejected. Poorer performance in L2 speakers was accompanied by increased activity in the medial superior frontal gyrus (SFG), indicating the additional recruitment of executive control mechanisms. In addition, post-hoc within-group comparisons of behavioral and neural correlates provide evidence for dual-mechanism models in older adults, suggesting that language processing involves both procedural and declarative memory systems. Moreover, we demonstrated that speaking an L2 requires more executive control and relies to a lesser extent on the procedural memory system than speaking one's own native language.