Neuroanatomical Evidence in Support of the Bilingual Advantage Theory

Bilingual Language Control in the Brain: Evidence from Structural and Effective Functional Brain Connectivity

Experience in bilingual language control is often accompanied by changes in the structure and function of the brain. Brain structural changes are also often closely related to changes in functions. Previous studies, however, have not directly explored the relationship between structural connectivity and effective functional connectivity of the brain during bilingual language control, and whether the two types of connectivity are associated with behavioral performance of language control. Using behavioral performance, functional, and diffusion imaging techniques, we found that: (1) during language control, the left dorsal lateral prefrontal cortex (dlPFC), left caudate nucleus (CN), inferior parietal lobe, precuneus, and dorsal anterior cingulate cortex (dACC)/pre-SMA were significantly activated. (2) In the language control model with left dlPFC, dACC/pre-SMA, and left CN as ROIs (selected based on activation results and language control models from previous studies), stimuli first enter dACC/pre-SMA and then to left CN. At the left CN, a bidirectional effective connectivity is formed with left dlPFC. (3) There is a nonlinear relationship between effective connectivity during language control and the structural connectivity of the second language learners' brains. Specifically, the fiber density between dACC/pre-SMA and left dlPFC has a positive influence on the bidirectional effective connectivity between left dlPFC and left CN. Findings of the present study contribute evidence toward functional effective connectivity during bilingual language control; toward structural connectivity in the brains of second language learners; as well as toward nonlinear relationships between functional effective connectivity, structural connectivity, and behavioral performance in relation to bilingual language control.

Voxel-wise multivariate analysis of brain-psychosocial associations in adolescents reveals six latent dimensions of cognition and psychopathology

BACKGROUND

Adolescence heralds the onset of much psychopathology, which may be conceptualized as an emergence of altered covariation between symptoms and brain measures. Multivariate methods can detect such modes of covariation or latent dimensions, but none specifically relating to psychopathology have yet been found using population-level structural brain data. Using voxel-wise (instead of parcellated) brain data may strengthen latent dimensions' brain-psychosocial relationships, but this creates computational challenges.

METHODS

We obtained voxel-wise grey matter density and psychosocial variables from the baseline (aged 9-10 years) Adolescent Brain and Cognitive Development cohort (n=11288), and employed a state-of-the-art segmentation method, sparse partial least squares, and a rigorous machine learning framework to prevent overfitting.

RESULTS

We found six latent dimensions, four pertaining specifically to mental health. The mental health dimensions related to overeating, anorexia/internalizing, oppositional symptoms (all p<0.002) and ADHD symptoms (p=0.03). ADHD related to increased and internalizing related to decreased grey matter density in dopaminergic and serotonergic midbrain areas, whereas oppositional symptoms related to increased grey matter in a noradrenergic nucleus. Internalizing related to increased and oppositional symptoms to reduced grey matter density in insula, cingulate and auditory cortices. Striatal regions featured strongly, with reduced caudate nucleus grey matter in ADHD, and reduced putamen grey matter in oppositional/conduct problems. Voxel-wise grey matter density generated stronger brain-psychosocial correlations than brain parcellations.

CONCLUSIONS

Voxel-wise brain data strengthen latent dimensions of brain-psychosocial covariation and sparse multivariate methods increase their psychopathological specificity. Internalizing and externalizing are associated with opposite grey matter changes in similar cortical and subcortical areas.

Does Diglossia Impact Brain Structure? Data from Swiss German Early Diglossic Speakers

(1) Background: Bilingualism has been reported to shape the brain by inducing cortical changes in cortical and subcortical language and executive networks. Similar yet different to bilingualism, diglossia is common in Switzerland, where the German-speaking population switches between an everyday spoken Swiss German (CH-GER) dialect and the standard German (stGER) used for reading and writing. However, no data are available for diglossia, defined as the use of different varieties or dialects of the same language, regarding brain structure. The aim of our study is to investigate if the presence of this type of diglossia has an impact on the brain structure, similar to the effects seen in bilingualism. (2) Methods: T1-weighted anatomical MRI scans of participants were used to compare the grey matter density and grey matter volume of 22 early diglossic CH-GER-speaking and 20 non-diglossic French-speaking right-handed university students, matched for age, linguistics and academic background. The images were processed with Statistical Parametric Mapping SPM12 and analyzed via voxel- and surface-based morphometry. (3) Results: A Bayesian ANCOVA on the whole brain revealed no differences between the groups. Also, for the five regions of interest (i.e., planum temporale, caudate nucleus, ACC, DLPFC and left interior parietal lobule), no differences in the cortical volume or thickness were found using the same statistical approach. (4) Conclusion: The results of this study may suggest that early diglossia does not shape the brain structure in the same manner as bilingualism.

Exploring the ventral white matter language network in bimodal and unimodal bilinguals

We used diffusion magnetic resonance imaging tractography to investigate the effect of language modality on the anatomy of the ventral white matter language network by comparing unimodal (Italian/English) and bimodal bilinguals (Italian/Italian Sign Language). We extracted the diffusion tractography measures of the Inferior Longitudinal fasciculus (ILF), Uncinate fasciculus (UF) and Inferior Fronto-Occipital fasciculus (IFOF) and we correlated them with the degree of bilingualism and the individual performance in fluency tasks. For both groups of bilinguals, the microstructural properties of the right ILF were correlated with individual level of proficiency in L2, confirming the involvement of this tract in bilingualism. In addition, we found that the degree of left lateralization of the ILF predicted the performance in semantic fluency in L1. The microstructural properties of the right UF correlated with performance in phonological fluency in L1, only for bimodal bilinguals. Overall, the pattern shows both similarities and differences between the two groups of bilinguals.

Gray matter volume differences between early bilinguals and monolinguals: A study of children and adults

Gray matter has been shown to be greater in early bilingual adults relative to monolingual adults in regions associated with language (Mechelli et al., 2004), and executive control (EC; Olulade et al., 2016). It is not known, however, if language experience-dependent differences in gray matter volume (GMV) exist in children. Further, any such differences are likely not to be the same as those observed in early bilingual adults, as children have had relatively shorter duration of dual-language exposure and/or less development of brain regions serving EC. We tested these predictions by comparing GMV in Spanish-English early bilingual and English monolingual children, and Spanish-English early bilingual and English monolingual adults (n = 122). Comparing only children revealed relatively more GMV in the bilinguals in bilateral frontal, right inferior frontal, and right superior parietal cortices (regions associated with EC). Bilinguals, however, had less GMV in left inferior parietal cortex (region associated with language). An ANOVA including these children with bilingual and monolingual adults revealed interactions of Language Background by Age Group. There were no regions of more GMV in bilinguals relative to monolinguals that were less pronounced in children than adults, despite the children's shorter dual-language experience. There were relative differences between bilingual and monolingual children that were more pronounced than those in adults in left precentral gyrus and right superior parietal lobule (close to, but not directly in areas associated with EC). Together, early bilingual children manifest relative differences in GMV, and, surprisingly, these do not diverge much from those observed in studies of bilingual adults.

Functional neuroanatomy of English word reading in early bilingual and monolingual adults

Skilled reading is important in daily life. While the understanding of the neurofunctional organization of this uniquely human skill has advanced significantly, it does not take into consideration the common bilingual experiences around the world. To examine the role of early bilingualism on the neural substrates supporting English word processing, we compared brain activity, as well as functional connectivity, in Spanish-English early bilingual adults (N = 25) and English monolingual adults (N = 33) during single-word processing. Activation analysis revealed no significant differences between the two groups. A seed-to-voxel analysis using eight a priori selected seed-regions (placed in regions known to be involved in reading) revealed relatively stronger functional connectivity in bilinguals between two sets of regions: left superior temporal gyrus seed positively with left lingual gyrus and left middle frontal gyrus seed negatively with left anterior cingulate cortex. Together these results suggest that an early Spanish-English bilingual experience does not modulate local brain activity for English word reading. It does, however, have some influence on the functional intercommunication between brain regions during reading, specifically in two regions associated with reading, which are functionally connected to those inside and outside of the reading network. We conclude that brain regions involved in processing English words are not that different in Spanish-English early bilingual adults relative to monolingual adult users of English.

French Phonological Component Analysis and aphasia recovery: A bilingual perspective on behavioral and structural data

Studies show bilingualism entails an advantage in cognitive control tasks. There is evidence of a bilingual advantage in the context of aphasia, resulting in better cognitive outcomes and recovery in bilingual persons with aphasia compared to monolingual peers. This bilingual advantage also results in structural changes in the right hemisphere gray matter. Very few studies have examined the so-called bilingual advantage by reference to specific anomia therapy efficacy. This study aims to compare the effect of French-Phonological Component Analysis (Fr-PCA) in monolinguals and bilingual persons with aphasia, both at the linguistic and cognitive control level, and to examine the structural impact of left hemisphere lesion location and right hemisphere structural data. Eight participants with chronic aphasia received Fr-PCA for a total of 15 h over 5 weeks. The results showed improved accuracy for treated words and generalization to untreated items and discourse in both groups, and improved Flanker task performance for some participants. Bilingual participants improved more than monolinguals for picture-naming tasks and narrative discourse. Damage to the left postcentral gyrus and the middle frontal gyrus was associated with less therapy-induced improvement. Additionally, left hemisphere damage to the inferior parietal gyrus and postcentral gyrus was associated with reduced cognitive control pre-therapy. Undamaged right hemisphere cortical thicknesses were significantly different between groups; the inferior frontal gyrus and the middle frontal gyrus were greater for the bilingual participants and correlated with cognitive control skills. These results suggest a bilingual advantage in anomia recovery following Fr-PCA, potentially resulting from enhanced cognitive control abilities that could be supported by right hemisphere neural reserve.

The Differences in Structure and Function of the Cerebellum Between Cantonese-Mandarin Bilinguals and Mandarin Monolinguals: a Multi-model MRI Study

The effects of the long-term bilingual experience on structure and function of the cerebellum remain unclear. To explore whether there are differences in cerebellar gray matter structure between Cantonese-Mandarin bilinguals and Mandarin monolinguals and whether these different cerebellar structures have different resting-state functional connectivity (RSFC) with the cerebrum between the two groups, 30 Cantonese-Mandarin bilingual and 30 Mandarin monolingual college students were scanned by the T1-weighted magnetic resonance imaging (MRI) and resting-state functional MRI. Voxel-based morphology (VBM) analysis and RSFC analysis were used to analyze the cerebellar gray matter volume (GMV) and cerebellar-cerebro functional connectivity, respectively. Correlation analysis was performed between GMV/RSFC and the rapid automatized naming (RAN) and cognitive control. Compared to Mandarin monolinguals, Cantonese-Mandarin bilinguals showed larger GMV in bilateral cerebellar inferior posterior lobe (including bilateral VIIIa, VIIIb,IX, and right X, Vermis VIIIb, and Vermis IX) and a significant increase in RSFC coupling of the right inferior cerebellar posterior lobe with orbital part of left inferior frontal gyrus (IFG). In addition, there was a positive correlation between average response time (RT) of Mandarin alphanumeric RAN and RSFC between the right inferior posterior lobe of cerebellum and left IFG of all participants. The long-term Cantonese-Mandarin bilingual experience can increase the GMV of the bilateral cerebellar inferior posterior lobe and the RSFC between the right inferior cerebellar posterior lobe with orbital part of left inferior frontal gyrus (IFG).

Dynamic Effects of Immersive Bilingualism on Cortical and Subcortical Grey Matter Volumes

Bilingualism has been shown to induce neuroplasticity in the brain, but conflicting evidence regarding its specific effects in grey matter continues to emerge, probably due to methodological differences between studies, as well as approaches that may miss the variability and dynamicity of bilingual experience. In our study, we devised a continuous score of bilingual experiences and we investigated their non-linear effects on regional GM volume in a sample of young healthy participants from an immersive and naturalistic bilingual environment. We focused our analyses on cortical and subcortical regions that had been previously proposed as part of the bilingual speech pipeline and language control network. Our results showed a non-linear relationship between bilingualism score and grey matter volume of the inferior frontal gyrus. We also found linear increases in volumes of putamen and cerebellum as a function of bilingualism score. These results go in line with predictions for immersive and naturalistic bilingual environments with increased intensity and diversity of language use and provide further evidence supporting the dynamicity of bilingualism’s effects on brain structure.

Influences of First and Second Language Phonology on Spanish Children Learning to Read in English

Children learning to read in two different orthographic systems are exposed to cross-linguistic interferences. We explored the effects of school (Monolingual, Bilingual) and grade (2nd, 4th, and 6th) on phonological activation during a visual word recognition task. Elementary school children from Spain completed a lexical decision task in English. The task included real words and pseudohomophones following Spanish or English phonological rules. Using the mouse-tracking paradigm, we analyzed errors, reaction times, and computer mouse movements. Children in the bilingual school performed better than children in the monolingual school. Children in higher grades performed better than children in lower grades. The interference effect of Spanish phonology was weak and became weaker in higher grades. Spanish children differentiate between first and second language grapheme-to-phoneme correspondences since early on in the educational process. In 6th grade, children from the bilingual school responded better to words and Spanish pseudohomophones, while children from the monolingual school were less distracted by the English pseudohomophones. Children in the bilingual school had stronger inhibition of Spanish (L1) phonology and stronger activation of English (L2) phonology. Instructional method plays an important role on the processing strategies Spanish children rely on when reading in English. School and grade influence the link between orthographic and phonological representations.

Bilinguals' speech perception in noise: Perceptual and neural associations

The current study characterized subcortical speech sound processing among monolinguals and bilinguals in quiet and challenging listening conditions and examined the relation between subcortical neural processing and perceptual performance. A total of 59 normal-hearing adults, ages 19–35 years, participated in the study: 29 native Hebrew-speaking monolinguals and 30 Arabic-Hebrew-speaking bilinguals. Auditory brainstem responses to speech sounds were collected in a quiet condition and with background noise. The perception of words and sentences in quiet and background noise conditions was also examined to assess perceptual performance and to evaluate the perceptual-physiological relationship. Perceptual performance was tested among bilinguals in both languages (first language (L1-Arabic) and second language (L2-Hebrew)). The outcomes were similar between monolingual and bilingual groups in quiet. Noise, as expected, resulted in deterioration in perceptual and neural responses, which was reflected in lower accuracy in perceptual tasks compared to quiet, and in more prolonged latencies and diminished neural responses. However, a mixed picture was observed among bilinguals in perceptual and physiological outcomes in noise. In the perceptual measures, bilinguals were significantly less accurate than their monolingual counterparts. However, in neural responses, bilinguals demonstrated earlier peak latencies compared to monolinguals. Our results also showed that perceptual performance in noise was related to subcortical resilience to the disruption caused by background noise. Specifically, in noise, increased brainstem resistance (i.e., fewer changes in the fundamental frequency (F0) representations or fewer shifts in the neural timing) was related to better speech perception among bilinguals. Better perception in L1 in noise was correlated with fewer changes in F0 representations, and more accurate perception in L2 was related to minor shifts in auditory neural timing. This study delves into the importance of using neural brainstem responses to speech sounds to differentiate individuals with different language histories and to explain inter-subject variability in bilinguals’ perceptual abilities in daily life situations.

General principles governing the amount of neuroanatomical overlap between languages in bilinguals

The literature has identified many important factors affecting the extent to which languages in bilinguals rely on the same neural populations in the specific brain region. The factors include the age of acquisition of the second language (L2), proficiency level of the first language (L1) and L2, and the amount of language exposure, among others. What is lacking is a set of global principles that explain how the many factors relate to the degree to which languages overlap neuroanatomically in bilinguals. We are offering a set of such principles that together account for the numerous sources of data that have been examined individually but not collectively: (1) the principle of acquisition similarity between L1 and L2, (2) the principle of linguistic similarity between L1 and L2, and (3) the principle of cognitive control and effort. Referencing the broad characteristics of language organization in bilinguals, as presented by the principles, can provide a roadmap for future clinical and basic science research.

Evidence for cognitive and brain reserve supporting executive control of memory in lifelong bilinguals

Recent bilingualism research attempts to understand whether continually controlling multiple languages provides domain-general benefits to other aspects of cognition. Yet little attention has been given to whether this extends to resistance to proactive interference (PI), which involves the filtering of irrelevant memory traces in order to focus attention on relevant to-be-remembered information. The present study sought to determine whether bilingualism provides benefits to resistance to PI performance and brain structure in regions supporting executive control of memory. Eighty-two younger and older adult participants, half English monolinguals and half highly proficient Spanish-English bilinguals, completed directed forgetting and release from PI tasks and underwent an MRI scan that measured cortical volume, thickness, and white matter integrity. While behavioral performance between bilinguals and monolinguals did not differ, bilinguals displayed thinner cortex in brain regions related to resistance to PI, providing evidence for cognitive reserve, and showed positive relationships between white matter integrity and resistance to PI performance, indicative of brain reserve. This study is the first to demonstrate cognitive reserve and brain reserve in different brain structure indices within the same healthy participants and suggests that bilingualism supports important structural relationships between regions necessary for executive control of memory.

Bilingualism: Pathway to Cognitive Reserve

Cognitive reserve is characterized by a dissociation between cognitive level and brain structure, thereby reducing the impact of deteriorating brain structure on cognitive function. Cognitive reserve is therefore a promising approach to maintaining cognitive function and protecting against symptoms of dementia. The present paper evaluates evidence supporting the claim that bilingualism contributes to cognitive reserve. Four types of evidence are presented: (i) brain and cognitive function in healthy aging, (ii) age of onset of symptoms of dementia, (iii) relation between clinical level and neuropathology for patients, and (iv) rate of cognitive decline in later stages of dementia. In all cases, bilinguals revealed patterns that were consistent with the interpretation of protection from cognitive reserve when compared with monolinguals.

The Differences in the Whole-Brain Functional Network between Cantonese-Mandarin Bilinguals and Mandarin Monolinguals

Cantonese-Mandarin bilinguals are logographic-logographic bilinguals that provide a unique population for bilingual studies. Whole brain functional connectivity analysis makes up for the deficiencies of previous bilingual studies on the seed-based approach and helps give a complete picture of the brain connectivity profiles of logographic-logographic bilinguals. The current study is to explore the effect of the long-term logographic-logographic bilingual experience on the functional connectivity of the whole-brain network. Thirty Cantonese-Mandarin bilingual and 30 Mandarin monolingual college students were recruited in the study. Resting state functional magnetic resonance imaging (rs-fMRI) was performed to investigate the whole-brain functional connectivity differences by network-based statistics (NBS), and the differences in network efficiency were investigated by graph theory between the two groups (false discovery rate corrected for multiple comparisons, q = 0.05). Compared with the Mandarin monolingual group, Cantonese-Mandarin bilinguals increased functional connectivity between the bilateral frontoparietal and temporal regions and decreased functional connectivity in the bilateral occipital cortex and between the right sensorimotor region and bilateral prefrontal cortex. No significant differences in network efficiency were found between the two groups. Compared with the Mandarin monolinguals, Cantonese-Mandarin bilinguals had no significant discrepancies in network efficiency. However, the Cantonese-Mandarin bilinguals developed a more strongly connected subnetwork related to language control, inhibition, phonological and semantic processing, and memory retrieval, whereas a weaker connected subnetwork related to visual and phonology processing, and speech production also developed.

Bilingualism and domain-general cognitive functions from a neural perspective: A systematic review

A large body of research has indicated that bilingualism - through continual practice in language control - may impact cognitive functions, as well as relevant aspects of brain function and structure. The present review aimed to bring together findings on the relationship between bilingualism and domain-general cognitive functions from a neural perspective. The final sample included 210 studies, covering findings regarding neural responses to bilingual language control and/or domain-general cognitive tasks, as well as findings regarding effects of bilingualism on non-task-related brain function and brain structure. The evidence indicates that a) bilingual language control likely entails neural mechanisms responsible for domain-general cognitive functions; b) bilingual experiences impact neural responses to domain-general cognitive functions; and c) bilingual experiences impact non-task-related brain function (both resting-state and metabolic function) as well as aspects of brain structure (both macrostructure and microstructure), each of which may in turn impact mental processes, including domain-general cognitive functions. Such functional and structural neuroplasticity associated with bilingualism may contribute to both cognitive and neural reserves, producing benefits across the lifespan.

The effect of bilingualism on brain development from early childhood to young adulthood

Bilingualism affects the structure of the brain in adults, as evidenced by experience-dependent grey and white matter changes in brain structures implicated in language learning, processing, and control. However, limited evidence exists on how bilingualism may influence brain development. We examined the developmental patterns of both grey and white matter structures in a cross-sectional study of a large sample (n = 711 for grey matter, n = 637 for white matter) of bilingual and monolingual participants, aged 3–21 years. Metrics of grey matter (thickness, volume, and surface area) and white matter (fractional anisotropy and mean diffusivity) were examined across 41 cortical and subcortical brain structures and 20 tracts, respectively. We used generalized additive modelling to analyze whether, how, and where the developmental trajectories of bilinguals and monolinguals might differ. Bilingual and monolingual participants manifested distinct developmental trajectories in both grey and white matter structures. As compared to monolinguals, bilinguals showed: (a) more grey matter (less developmental loss) starting during late childhood and adolescence, mainly in frontal and parietal regions (particularly in the inferior frontal gyrus pars opercularis, superior frontal cortex, inferior and superior parietal cortex, and precuneus); and (b) higher white matter integrity (greater developmental increase) starting during mid-late adolescence, specifically in striatal–inferior frontal fibers. The data suggest that there may be a developmental basis to the well-documented structural differences in the brain between bilingual and monolingual adults.

A Meta-Analysis of Gray Matter Differences Between Bilinguals and Monolinguals

Bilingualism is of great interest to the neuroscience of language, and understanding the anatomical changes associated with second language learning help inform theories of bilingual advantage across the lifespan. While the literature on structural differences between bilinguals and monolinguals is robust, relatively few studies of gray matter (GM) have directly compared bilinguals with monolinguals in a whole-brain analysis. Overall, this and heterogeneity of study samples and methodology have led to a lack of clear anatomical support for major theories. Here, we engage in an activation likelihood estimate (ALE) meta-analysis of voxel-based morphometry (VBM) studies of GM for cases that directly compare bilingual and monolingual subjects in a whole-brain analysis. The analysis (sixteen foci, from ten contrasts across eight studies) resulted in one cluster located primarily within the anterior lobe of the right cerebellum. However, when the one pediatric study was removed, the analysis revealed no consistent results across the studies included in this meta-analysis. This suggests that for VBM studies of bilingual and monolingual adults there is considerable heterogeneity of results that complicate the understanding of the bilingual brain. Future studies will need to include larger, more well-defined samples and interrogate more fine-grained anatomical features such as cortical thickness and surface area in order to more fully examine the anatomical changes associated with bilingualism across the lifespan.

Employing Natural Control for Confounding Factors in the Hunt for the Bilingual Advantage in Attention: Evidence from School Children in Gibraltar

Does being bilingual convey a benefit in 'cognitive control'? Research on this question has been plagued by confounding geo-political factors which themselves might affect cognitive ability (e.g., Socio-Economic Status, immigration and culture). In the current study, we addressed this problem by exploring individuals of varying degrees of bilingualism from one and the same population, hence naturally controlling for confounding variables. The English/Spanish speaking population of Gibraltar share the same education, amenities, and culture on a very small landmass but vary in the degree to which they master multiple languages. We assessed the performance of 207 Gibraltarian children (9-10 yrs) on a battery of auditory attention tests and captured their degree of bilingualism via self-reported and 'objective' methods. We found at least 'moderate' evidence that measures of bilingualism cannot predict attentional ability. These results add to growing scepticism concerning the truthfulness of the claim that bilingualism conveys cognitive advantages.

An fMRI study of English and Spanish word reading in bilingual adults

Reading relies on a left-lateralized brain system, including occipito-temporal (OTC), temporo-parietal, and inferior frontal (IFC) cortices. Neuroimaging studies have investigated whether activation in these cortices is modulated by a language's orthographic depth (consistency of grapheme-to-phoneme conversion). In Spanish-English bilinguals, some but not all studies have reported activation differences between the two languages during reading. Here, we studied Spanish-English early bilingual adults living in the United States (N = 25; 17 females, 8 males). We examined local activity, functional connectivity, and spatially distributed activity patterns during English and Spanish word reading. We found overlap in local activity for the two languages in the left IFC, but no differences in activation between them and few differences in functional connectivity (none of which were in pairs of regions known to be involved in reading); yet, there were spatially distributed patterns of brain activity that differentiate English and Spanish in regions of bilateral cerebellum/left OTC, the left superior occipital gyrus, the left IFC, and the left medial frontal gyrus. Overall, we found no evidence for differences in local activation or functional connectivity during English versus Spanish word processing in regions known to be involved in reading, yet we found brain-based evidence that Spanish-English bilinguals distinguish between the two languages.

Turning languages on and off: Switching into and out of code-blends reveals the nature of bilingual language control

When spoken language (unimodal) bilinguals switch between languages, they must simultaneously inhibit 1 language and activate the other language. Because American Sign Language (ASL)-English (bimodal) bilinguals can switch into and out of code-blends (simultaneous production of a sign and a word), we can tease apart the cost of inhibition (turning a language off) and activation (turning a language on). Results from a cued picture-naming task with 43 bimodal bilinguals revealed a significant cost to turn off a language (switching out of a code-blend), but no cost to turn on a language (switching into a code-blend). Switching from single to dual lexical retrieval (adding a language) was also not costly. These patterns held for both languages regardless of default language, that is, whether switching between speaking and code-blending (English default) or between signing and code-blending (ASL default). Overall, the results support models of bilingual language control that assume a primary role for inhibitory control and indicate that disengaging from producing a language is more difficult than engaging a new language. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Age of acquisition impacts the brain differently depending on neuroanatomical metric

Although researchers generally agree that a certain set of brain areas underlie bilingual language processing, there is discrepancy regarding what effect timing of language acquisition has on these regions. We aimed to investigate the neuroanatomical correlates of age of acquisition (AoA), which has been examined previously, but with inconsistent results, likely influenced by methodological differences across studies. We analyzed gray matter density, volume, and thickness using whole-brain linear models in 334 bilinguals and monolinguals. Neuroanatomical correlates of AoA differed depending on gray matter metric. Relative to early bilinguals, late bilinguals had thicker cortex in language processing and cognitive control regions, and greater density in multiple frontal areas and the right middle temporal and supramarginal gyri. Early bilinguals had greater volume than late bilinguals in the left middle temporal gyrus. Overall, volume was the least sensitive to AoA-related differences. Multiple regions not classically implicated in dual-language processing were also found, which highlights the important role of whole-brain analyses in neuroscience. This is the first study to investigate AoA and gray matter thickness, volume, and density all in the same sample. We conclude that cognitive models of bilingualism should consider the roles of development and neuroanatomical metric in driving our understanding of bilingual and monolingual language organization.

Bilingual effects on lexical selection: A neurodevelopmental perspective

When a listener hears a word, multiple lexical items may come to mind; for instance, /kæn/ may activate concepts with similar phonological onsets such as candy and candle. Acquisition of two lexicons may increase such linguistic competition. Using functional Near-Infrared Spectroscopy neuroimaging, we investigate whether bilingualism impacts word processing in the child's brain. Bilingual and monolingual children (N = 52; ages 7-10) completed a lexical selection task in English, where participants adjudicated phonological competitors (e.g., car/cat vs. car/pen). Children were less accurate and responded more slowly during competing than non-competing items. In doing so, children engaged top-down fronto-parietal regions associated with cognitive control. In comparison to bilinguals, monolinguals showed greater activity in left frontal regions, a difference possibly due to bilinguals' adaptation for dual-lexicons. These differences provide insight to theories aiming to explain the role of experience on children's emerging neural networks for lexical selection and language processing.

Consequences of multilingualism for neural architecture

Language has the power to shape cognition, behavior, and even the form and function of the brain. Technological and scientific developments have recently yielded an increasingly diverse set of tools with which to study the way language changes neural structures and processes. Here, we review research investigating the consequences of multilingualism as revealed by brain imaging. A key feature of multilingual cognition is that two or more languages can become activated at the same time, requiring mechanisms to control interference. Consequently, extensive experience managing multiple languages can influence cognitive processes as well as their neural correlates. We begin with a brief discussion of how bilinguals activate language, and of the brain regions implicated in resolving language conflict. We then review evidence for the pervasive impact of bilingual experience on the function and structure of neural networks that support linguistic and non-linguistic cognitive control, speech processing and production, and language learning. We conclude that even seemingly distinct effects of language on cognitive operations likely arise from interdependent functions, and that future work directly exploring the interactions between multiple levels of processing could offer a more comprehensive view of how language molds the mind.

Different Features of Bilingualism in Relation to Executive Functioning

The notion that the long-term practice of managing two languages is beneficial for the executive control system is an ongoing debate. Criticism have been raised that studies demonstrating a bilingual advantage often suffer from small sample sizes, and do not control for fluid intelligence as a possible confound. Taking those suggested factors into account, focusing on older bilingual age groups and investigating the potential effects of linguistic distances, this study aimed to improve the interpretations of the bilinguals' advantages. Measures of inhibition (Flanker, Stroop, Simon task) and switching (Number-letter, Color-Shape, Local-global task) were collected in participants in the ages 50-75 years (n = 193). Despite a large study sample, results did not support any beneficial effects related to improve processing costs in executive functioning. Sub-analyses of the two different language groups (Swedish-Finnish / Swedish-English) intended to investigate the effect of linguistic distances did not change this outcome. Future studies exploring the potential long-term term effects of bilingualism would benefit from identifying tests of cognitive control with greater ecological validity and include other measures of cognitive functioning. Language learning interventions may also be a promising tool for future research.

Bilingualism reveals fundamental variation in language processing

Although variation in the ways individuals process language has long been a topic of interest and discussion in the psycholinguistic literature, only recently have studies of bilingualism and its cognitive consequences begun to reveal the fundamental dynamics between language and cognition. We argue that the active use of two languages provides a lens through which the interactions between language use, language processing, and the contexts in which these take place can be fully understood. Far from bilingualism being considered a special case, it may provide the common basis upon which the principles of language learning and use can be modeled.

The independent and interacting effects of socioeconomic status and dual-language use on brain structure and cognition

Family socioeconomic status (SES) is strongly associated with children's cognitive development, and past studies have reported socioeconomic disparities in both neurocognitive skills and brain structure across childhood. In other studies, bilingualism has been associated with cognitive advantages and differences in brain structure across the lifespan. The aim of the current study is to concurrently examine the joint and independent associations between family SES and dual-language use with brain structure and cognitive skills during childhood. A subset of data from the Pediatric Imaging, Neurocognition and Genetics (PING) study was analyzed; propensity score matching established an equal sample (N = 562) of monolinguals and dual-language users with similar socio-demographic characteristics (Mage = 13.5, Range = 3-20 years). When collapsing across all ages, SES was linked to both brain structure and cognitive skills. When examining differences by age group, brain structure was significantly associated with both income and dual-language use during adolescence, but not earlier in childhood. Additionally, in adolescence, a significant interaction between dual-language use and SES was found, with no difference in cortical surface area (SA) between language groups of higher-SES backgrounds but significantly increased SA for dual-language users from lower-SES families compared to SES-matched monolinguals. These results suggest both independent and interacting associations between SES and dual-language use with brain development. To our knowledge, this is the first study to concurrently examine dual-language use and socioeconomic differences in brain structure during childhood and adolescence.

Neuroplasticity across the lifespan and aging effects in bilinguals and monolinguals

Evidence that bilingualism protects against age-related neurocognitive decline is mixed. One relatively consistent finding is that bilingual seniors have greater grey matter volume (GMV) in regions implicated in executive control (EC) and language processing. Here, we compare the neuroplastic effects of bilingual experience on the EC network of young and aging populations directly, and for the first time we evaluate the extent to which such effects may predict executive control performance across age. We used GMV as an index of neural reserve and response time (RT) performance on the Flanker task for measuring EC efficiency. In the presence of age-related widespread GM deterioration, bilinguals had greater GMV than monolinguals in key regions of interest across age. Moreover, whereas EC performance in monolingual seniors was strictly related to GMV, this was not observed for bilingual seniors or younger participants in either group. Interactions between expected effects-of-age and language group on the relationships between GMV and RT suggested that bilingualism affords differential benefits across the lifespan. In younger participants, greater GMV offered no behavioral benefit on EC performance, whilst it did for seniors. It thus appears that age-related cognitive decline following GMV loss in the EC network is delayed in bilinguals.

How bilingualism protects the brain from aging: Insights from bimodal bilinguals

Bilingual experience can delay cognitive decline during aging. A general hypothesis is that the executive control system of bilinguals faces an increased load due to controlling two languages, and this increased load results in a more "tuned brain" that eventually creates a neural reserve. Here we explored whether such a neuroprotective effect is independent of language modality, i.e., not limited to bilinguals who speak two languages but also occurs for bilinguals who use a spoken and a signed language. We addressed this issue by comparing bimodal bilinguals to monolinguals in order to detect age-induced structural brain changes and to determine whether we can detect the same beneficial effects on brain structure, in terms of preservation of gray matter volume (GMV), for bimodal bilinguals as has been reported for unimodal bilinguals. Our GMV analyses revealed a significant interaction effect of age × group in the bilateral anterior temporal lobes, left hippocampus/amygdala, and left insula where bimodal bilinguals showed slight GMV increases while monolinguals showed significant age-induced GMV decreases. We further found through cortical surface-based measurements that this effect was present for surface area and not for cortical thickness. Moreover, to further explore the hypothesis that overall bilingualism provides neuroprotection, we carried out a direct comparison of GMV, extracted from the brain regions reported above, between bimodal bilinguals, unimodal bilinguals, and monolinguals. Bilinguals, regardless of language modality, exhibited higher GMV compared to monolinguals. This finding highlights the general beneficial effects provided by experience handling two language systems, whether signed or spoken. Hum Brain Mapp 38:4109-4124, 2017. © 2017 Wiley Periodicals, Inc.

Immersive bilingualism reshapes the core of the brain

Bilingualism has been shown to affect the structure of the brain, including cortical regions related to language. Less is known about subcortical structures, such as the basal ganglia, which underlie speech monitoring and language selection, processes that are crucial for bilinguals, as well as other linguistic functions, such as grammatical and phonological acquisition and processing. Simultaneous bilinguals have demonstrated significant reshaping of the basal ganglia and the thalamus compared to monolinguals. However, it is not clear whether these effects are due to learning of the second language (L2) at a very young age or simply due to continuous usage of two languages. Here, we show that bilingualism-induced subcortical effects are directly related to the amount of continuous L2 usage, or L2 immersion. We found significant subcortical reshaping in non-simultaneous (or sequential) bilinguals with extensive immersion in a bilingual environment, closely mirroring the recent findings in simultaneous bilinguals. Importantly, some of these effects were positively correlated to the amount of L2 immersion. Conversely, sequential bilinguals with comparable proficiency and age of acquisition (AoA) but limited immersion did not show similar effects. Our results provide structural evidence to suggestions that L2 acquisition continuously occurs in an immersive environment, and is expressed as dynamic reshaping of the core of the brain. These findings propose that second language learning in the brain is a dynamic procedure which depends on active and continuous L2 usage.