Structural plasticity of the left caudate in bimodal bilinguals

Bilinguals need an effective neural mechanism to select and control their languages for successful communication. Recent evidence indicates that the left caudate nucleus (LCN) is a critical part of this mechanism. Here we show that bimodal bilinguals, who use spoken and sign languages, have greater grey matter volume (GMV) in the head of the LCN as compared to monolinguals. We also found higher functional activation of this region in bimodal bilinguals when they switched between sign language and spoken language compared to when they did not switch languages. Furthermore, GMV was positively correlated with the magnitude of the switching effect in the head of the LCN. These findings indicate that for bimodal bilinguals, the LCN is shaped by bilingualism both anatomically and functionally.     

Right inferior frontal gyrus: An integrative hub in tonal bilinguals

Right hemispheric dominance in tonal bilingualism is still controversial. In this study, we investigated hemispheric dominance in 30 simultaneous Bai‐Mandarin tonal bilinguals and 28 Mandarin monolinguals using multimodal neuroimaging. Resting‐state functional connectivity (RSFC) analysis was first performed to reveal the changes of functional connections within the language‐related network. Voxel‐based morphology (VBM) and tract‐based spatial statistics (TBSS) analyses were then used to identify bilinguals' alterations in gray matter volume (GMV) and fractional anisotropy (FA) of white matter, respectively. RSFC analyses revealed significantly increased functional connections of the right pars‐orbital part of the inferior frontal gyrus (IFG) with right caudate, right pars‐opercular part of IFG, and left inferior temporal gyrus in Bai‐Mandarin bilinguals compared to monolinguals. VBM and TBSS analyses further identified significantly greater GMV in right pars‐triangular IFG and increased FA in right superior longitudinal fasciculus (SLF) in bilinguals than in monolinguals. Taken together, these results demonstrate the integrative role of the right IFG in tonal language processing of bilinguals. Our findings suggest that the intrinsic language network in simultaneous tonal bilinguals differs from that of monolinguals in terms of both function and structure.     

Electrophysiological measures of language processing in bilinguals

The aim of the present study was to investigate how multiple languages are represented in the human brain. Event-related brain potentials (ERPs) were recorded from right-handed polyglots and monolinguals during a task involving silent reading. The participants in the experiment were nine Italian monolinguals and nine Italian/Slovenian bilinguals of a Slovenian minority in Trieste; the bilinguals, highly fluent in both languages, had spoken both languages since birth. The stimuli were terminal words that would correctly complete a short, meaningful, previously shown sentence, or else were semantically or syntactically incorrect. The task consisted in deciding whether the sentences were well formed or not, giving the response by pressing a button. Both groups read the same set of 200 Italian sentences to compare the linguistic processing, while the bilinguals also received a set of 200 Slovenian sentences, comparable in complexity and length, to compare the processing of the two languages within the group. For the bilinguals, the ERP results revealed a strong, left-sided activation, reflected by the N1 component, of the occipitotemporal regions dedicated to orthographic processing, with a latency of about 150 msec for Slovenian words, but bilateral activation of the same areas for Italian words, which was also displayed by topographical mapping. In monolinguals, semantic error produced a long-lasting negative response (N2 and N4) that was greater over the right hemisphere, whereas syntactic error activated mostly the left hemisphere. Conversely, in the bilinguals, semantic incongruence resulted in greater response over the left hemisphere than over the right. In this group, the P615 syntactical error responses were of equal amplitude on both hemispheres for Italian words and greater on the right side for Slovenian words. The present findings support the view that there are interand intrahemispheric brain activation asymmetries when monolingual and bilingual speakers comprehend written language. The fact that the bilingual speakers in the present study were highly fluent and had acquired both languages in early infancy suggests that the brain activation patterns do not depend on the age of acquisition or the fluency level, as in the case of late, not-so-proficient L2 language learners, but on the functional organization of the bilinguals' brain due to polyglotism and based on brain plasticity.     

Bilingual and monolingual brains compared: a functional magnetic resonance imaging investigation of syntactic processing and a possible "neural signature" of bilingualism

Abstract Does the brain of a bilingual process language differently from that of a monolingual? We compared how bilinguals and monolinguals recruit classic language brain areas in response to a language task and asked whether there is a "neural signature" of bilingualism. Highly proficient and early-exposed adult Spanish-English bilinguals and English monolinguals participated. During functional magnetic resonance imaging (fMRI), participants completed a syntactic "sentence judgment task" [Caplan, D., Alpert, N., & Waters, G. Effects of syntactic structure and propositional number on patterns of regional cerebral blood flow. Journal of Cognitive Neuroscience, 10, 541-552, 1998]. The sentences exploited differences between Spanish and English linguistic properties, allowing us to explore similarities and differences in behavioral and neural responses between bilinguals and monolinguals, and between a bilingual's two languages. If bilinguals' neural processing differs across their two languages, then differential behavioral and neural patterns should be observed in Spanish and English. Results show that behaviorally, in English, bilinguals and monolinguals had the same speed and accuracy, yet, as predicted from the Spanish-English structural differences, bilinguals had a different pattern of performance in Spanish. fMRI analyses revealed that both monolinguals (in one language) and bilinguals (in each language) showed predicted increases in activation in classic language areas (e.g., left inferior frontal cortex, LIFC), with any neural differences between the bilingual's two languages being principled and predictable based on the morphosyntactic differences between Spanish and English. However, an important difference was that bilinguals had a significantly greater increase in the blood oxygenation level-dependent signal in the LIFC (BA 45) when processing English than the English monolinguals. The results provide insight into the decades-old question about the degree of separation of bilinguals' dual-language representation. The differential activation for bilinguals and monolinguals opens the question as to whether there may possibly be a "neural signature" of bilingualism. Differential activation may further provide a fascinating window into the language processing potential not recruited in monolingual brains and reveal the biological extent of the neural architecture underlying all human language.     

Differences in word recognition between early bilinguals and monolinguals: behavioral and ERP evidence

We investigated the behavioral and brain responses (ERPs) of bilingual word recognition to three fundamental psycholinguistic factors, frequency, morphology, and lexicality, in early bilinguals vs. monolinguals. Earlier behavioral studies have reported larger frequency effects in bilinguals' nondominant vs. dominant language and in some studies also when compared to corresponding monolinguals. In ERPs, language processing differences between bilinguals vs. monolinguals have typically been found in the N400 component. In the present study, highly proficient Finnish-Swedish bilinguals who had acquired both languages during childhood were compared to Finnish monolinguals during a visual lexical decision task and simultaneous ERP recordings. Behaviorally, we found that the response latencies were overall longer in bilinguals than monolinguals, and that the effects for all three factors, frequency, morphology, and lexicality were also larger in bilinguals even though they had acquired both languages early and were highly proficient in them. In line with this, the N400 effects induced by frequency, morphology, and lexicality were larger for bilinguals than monolinguals. Furthermore, the ERP results also suggest that while most inflected Finnish words are decomposed into stem and suffix, only monolinguals have encountered high frequency inflected word forms often enough to develop full-form representations for them. Larger behavioral and neural effects in bilinguals in these factors likely reflect lower amount of exposure to words compared to monolinguals, as the language input of bilinguals is divided between two languages.     

Structural correlates for lexical efficiency and number of languages in non-native speakers of English

We used structural magnetic resonance imaging (MRI) and voxel based morphometry (VBM) to investigate whether the efficiency of word processing in the non-native language (lexical efficiency) and the number of non-native languages spoken (2+ versus 1) were related to local differences in the brain structure of bilingual and multilingual speakers. We dissociate two different correlates for non-native language processing. Firstly, multilinguals who spoke 2 or more non-native languages had higher grey matter density in the right posterior supramarginal gyrus compared to bilinguals who only spoke one non-native language. This is interpreted in relation to previous studies that have shown that grey matter density in this region is related to the number of words learnt in bilinguals relative to monolinguals and in monolingual adolescents with high versus low vocabulary. Our second result was that, in bilinguals, grey matter density in the left pars opercularis was positively related to lexical efficiency in second language use, as measured by the speed and accuracy of lexical decisions and the number of words produced in a timed verbal fluency task. Grey matter in the same region was also negatively related to the age at which the second language was acquired. This is interpreted in terms of previous findings that associated the left pars opercularis with phonetic expertise in the native language.     

Language lateralisation in late proficient bilinguals: a lexical decision fMRI study

Approximately half the world's population can now speak more than one language. Understanding the neural basis of language organisation in bilinguals, and whether the cortical networks involved during language processing differ from that of monolinguals, is therefore an important area of research. A main issue concerns whether L2 (second language) is processed using the same neural mechanisms that mediate L1 (first language) processing. Moderating factors include the age of L2 acquisition and the level of proficiency. Here we used a lexical decision task with five conditions during functional magnetic resonance imaging (fMRI) to investigate language processing in eight late proficient bilinguals when using Macedonian (L1) and English (L2). Bilinguals had greater bilateral activation during both L1 and L2 processing, and therefore weaker language lateralisation, compared to matched control English monolinguals. A greater amount of overall activation was also seen in bilinguals, especially during L2 conditions. Late proficient bilinguals living in their L2 environment employ a more extensive neural network than monolinguals when processing their second language.     

Language, modality and the brain

Studies of the signed languages of deaf people have shown that fully expressive languages can arise, outside of the mainstream of spoken languages, that exhibit the complexities of linguistic organization found in all spoken languages. Thus, the human capacity for language is not linked to some privileged cognitive-auditory connection. However, the formal properties of languages (spoken or signed) appear to be highly conditioned by the modalities involved in their perception and production. Multi-layering of linguistic elements and the use of space in the service of syntax appear to be modality-determined aspects of signed languages. Analyses of patterns of breakdown of signed languages provide new perspectives on the nature of cerebral organization for language. The studies reviewed in this article show that the left cerebral hemisphere in man is specialized for signed as well as spoken languages, and thus may have an innate predisposition for language, independent of language modality.     

Functional neuroanatomy of arithmetic in monolingual and bilingual adults and children

Prior studies on the brain bases of arithmetic have not focused on (or even described) their participants'' language backgrounds. Yet, unlike monolinguals, early bilinguals have the capacity to solve arithmetic problems in both of their two languages. This raises the question whether this ability, or any other experience that comes with being bilingual, affects brain activity for arithmetic in bilinguals relative to monolinguals. Here, we used functional magnetic resonance imaging to compare brain activity in 44 English monolinguals and 44 Spanish‐English early bilinguals, during the solving of arithmetic problems in English. We used a factorial design to test for a main effect of bilingual Language Experience. Based on the known modulating roles of arithmetic operation and age, we used two arithmetic tasks (addition and subtraction) and studied two age groups (adults and children). When collapsing across operations and age, we found broad bilateral activation for arithmetic in both the monolingual group and the bilingual group. However, an analysis of variance revealed that there was no effect of Language Experience, nor an interaction of Language Experience with Operation or Age Group. Bayesian analyses within regions of interest chosen for their role in arithmetic further supported the finding of no effect of Language Experience on brain activity underlying arithmetic. We conclude that early bilingualism does not influence the functional neuroanatomy of simple arithmetic.     

Language laterality in English/Welsh bilinguals: Language-acquisitional and language-specific factors in the development of lateralisation

In order to test the hypothesis that monolinguals differ from bilinguals in their pattern of language lateralisation and to examine the relative merits of language-acquisitional versus language-specific factors, two experiments involving divided screen presentation of two languages were conducted using Welsh/English speaking participants. In the first experiment 80 monolingual teenagers were compared to 80 bilingual teenagers on a tachistoscopic "visual half-field" test of Welsh and English nouns and verbs. ANOVA revealed a greater left hemisphere advantage for Welsh-English bilinguals as compared to English monolinguals. Thus, in contrast to previous studies, in our bilinguals there was evidence of greater left hemisphere involvement in the processing of language. In the second experiment, four separate groups of 40 teenagers, varying in the age and manner of acquisition of their languages, were compared on the same test of Welsh and English words. These groups can be viewed as graded from the early to late bilinguals. ANOVA revealed a greater left hemisphere advantage when processing Welsh as compared to English words for all four groups. However no significant difference was observed between the four groups in respect of laterality for Welsh and English, indicating an equally greater left hemisphere bias for all four groups when processing Welsh words. We discuss these results in terms of a language-specific effect and suggest the specific orthography of the Welsh language (for individually presented nouns and verbs) promotes a left hemisphere advantage over and above language-acquisitional factors.     

Language laterality in English/Welsh bilinguals: language-acquisitional and language-specific factors in the development of lateralisation

In order to test the hypothesis that monolinguals differ from bilinguals in their pattern of language lateralisation and to examine the relative merits of language-acquisitional versus language-specific factors, two experiments involving divided screen presentation of two languages were conducted using Welsh/English speaking participants. In the first experiment 80 monolingual teenagers were compared to 80 bilingual teenagers on a tachistoscopic "visual half-field" test of Welsh and English nouns and verbs. ANOVA revealed a greater left hemisphere advantage for Welsh-English bilinguals as compared to English monolinguals. Thus, in contrast to previous studies, in our bilinguals there was evidence of greater left hemisphere involvement in the processing of language. In the second experiment, four separate groups of 40 teenagers, varying in the age and manner of acquisition of their languages, were compared on the same test of Welsh and English words. These groups can be viewed as graded from the early to late bilinguals. ANOVA revealed a greater left hemisphere advantage when processing Welsh as compared to English words for all four groups. However no significant difference was observed between the four groups in respect of laterality for Welsh and English, indicating an equally greater left hemisphere bias for all four groups when processing Welsh words. We discuss these results in terms of a language-specific effect and suggest the specific orthography of the Welsh language (for individually presented nouns and verbs) promotes a left hemisphere advantage over and above language-acquisitional factors.     

Converging evidence for left hemisphere language lateralization in bilinguals

A previous study [1] demonstrated that when subject and experimental variables are controlled, similar levels of left hemisphere language lateralization are obtained in bilinguals and monolinguals. The present study used the same group of bilinguals (adult, late acquirers of their second language) in an auditory lateralization task. A similar degree of left hemisphere asymmetry was again obtained for the bilinguals' two languages and for the monolinguals. Furthermore, the individual performances of the bilinguals—within the present task and across visual and auditory tasks—paralleled those of monolinguals. Thus, converging evidence is provided for equal levels of left hemisphere language dominance in bilinguals and monolinguals.     

Good Language-Switchers are Good Task-Switchers: Evidence from Spanish-English and Mandarin-English Bilinguals

Bilingual advantages in executive control tasks are well documented, but it is not yet clear what degree or type of bilingualism leads to these advantages. To investigate this issue, we compared the performance of two bilingual groups and monolingual speakers in task-switching and language-switching paradigms. Spanish-English bilinguals, who reported switching between languages frequently in daily life, exhibited smaller task-switching costs than monolinguals after controlling for between-group differences in speed and parent education level. By contrast, Mandarin-English bilinguals, who reported switching languages less frequently than Spanish-English bilinguals, did not exhibit a task-switching advantage relative to monolinguals. Comparing the two bilingual groups in language-switching, Spanish-English bilinguals exhibited smaller costs than Mandarin-English bilinguals, even after matching for fluency in the non-dominant language. These results demonstrate an explicit link between language-switching and bilingual advantages in task-switching, while also illustrating some limitations on bilingual advantages. (JINS, 2011, 17, 682-691).     

Individual differences in control of language interference in late bilinguals are mainly related to general executive abilities

Background  

Recent research based on comparisons between bilinguals and monolinguals postulates that bilingualism enhances cognitive control functions, because the parallel activation of languages necessitates control of interference. In a novel approach we investigated two groups of bilinguals, distinguished by their susceptibility to cross-language interference, asking whether bilinguals with strong language control abilities ("non-switchers") have an advantage in executive functions (inhibition of irrelevant information, problem solving, planning efficiency, generative fluency and self-monitoring) compared to those bilinguals showing weaker language control abilities ("switchers").     

Laterality and language experience

A meta-analysis was conducted on studies that examined hemispheric functional asymmetry for language in brain-intact monolingual and bilingual adults. Data from 23 laterality studies that directly compared bilingual and monolingual speakers on the same language were analysed (n = 1234). Variables examined were language experience (monolingual, bilingual), experimental paradigm (dichotic listening, visual hemifield presentation, and dual task) and, among bilinguals, the influence of second language proficiency (proficient vs nonproficient) and onset of bilingualism (early, or before age 6; and late, or after age 6). Overall, monolinguals and late bilinguals showed reliable left hemisphere dominance, while early bilinguals showed reliable bilateral hemispheric involvement. Within bilinguals, there was no reliable effect of language proficiency when age of L2 acquisition was controlled. The findings indicate that early learning of one vs. two languages predicts divergent patterns of cerebral language lateralisation in adulthood.     

Second language interferes with word production in fluent bilinguals: brain potential and functional imaging evidence

Bilingual individuals need effective mechanisms to prevent interference between their languages. Using event-related brain potentials (ERPs) and functional magnetic resonance imaging (fMRI), we present evidence for interference of phonological information from the nontarget language in German-Spanish bilinguals. A tacit picture-naming task was used in which bilinguals and monolinguals had to make speeded responses based on the first letter of the picture's name in the target language. In one condition, subjects were required to respond when the name began with a vowel and to withhold a response if it started with a consonant. Stimuli had been selected such that in half of the trials, the names in both languages necessitated the same response, whereas in the other half, responses were different for the two languages. For the bilinguals, the language in which the stimuli had to be named was changed after each block. Bilinguals showed phonological interference compared with monolingual performance, which was evident in their performance, ERPs, and fMRI patterns. Nonlanguagespecific brain areas such as the left middle prefrontal cortex were found to be crucial for the control of interference.     

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.     

Laterality and language experience

A meta-analysis was conducted on studies that examined hemispheric functional asymmetry for language in brain-intact monolingual and bilingual adults. Data from 23 laterality studies that directly compared bilingual and monolingual speakers on the same language were analysed (n?=?1234). Variables examined were language experience (monolingual, bilingual), experimental paradigm (dichotic listening, visual hemifield presentation, and dual task) and, among bilinguals, the influence of second language proficiency (proficient vs nonproficient) and onset of bilingualism (early, or before age 6; and late, or after age 6). Overall, monolinguals and late bilinguals showed reliable left hemisphere dominance, while early bilinguals showed reliable bilateral hemispheric involvement. Within bilinguals, there was no reliable effect of language proficiency when age of L2 acquisition was controlled. The findings indicate that early learning of one vs. two languages predicts divergent patterns of cerebral language lateralisation in adulthood.     

Hemisphere lateralization is influenced by bilingual status and composition of words

It has been generally accepted that the left hemisphere is more functionally specialized for language than the right hemisphere for right-handed monolinguals. But more and more studies have also demonstrated right hemisphere advantage for some language tasks with certain participants. A recent comprehensive survey has shown that hemisphere lateralization of language depends on the bilingual status of the participants, with bilateral hemispheric involvement for both languages of early bilinguals, who acquired both languages by age of 6, left hemisphere dominance for language of monolinguals, and also left hemisphere dominance for both languages of late bilinguals, who acquired the second language after age of 6. We propose a preliminary model which takes into account both composition of stimulus words and bilingual status of participants to resolve the apparent controversies regarding hemisphere lateralization of various reading experiments in the literature with focus on Chinese characters, and to predict lateralization patterns for future experiments in Chinese word reading. The bilingual status includes early bilingual, late bilingual and monolingual. However, we have tested this model only with late Chinese-English bilingual participants by using a Stroop paradigm in this paper, though the aim of our model is to disentangle the controversies in the lateralization effect of Chinese character reading. We show here with stimuli written in Chinese single characters that the Stroop effect was stronger when the stimuli were presented to the right than to the left visual field, implying that the language information and color identification/naming may interact more strongly in the left hemisphere. Therefore, our experimental results indicate left hemisphere dominance for Chinese character processing, providing evidence for one part of our model.     

Age‐associated patterns in gray matter volume,cerebral perfusion and BOLD oscillations in children and adolescents

Healthy brain development involves changes in brain structure and function that are believed to support cognitive maturation. However, understanding how structural changes such as grey matter thinning relate to functional changes is challenging. To gain insight into structure‐function relationships in development, the present study took a data driven approach to define age‐related patterns of variation in gray matter volume (GMV), cerebral blood flow (CBF) and blood‐oxygen level dependent (BOLD) signal variation (fractional amplitude of low‐frequency fluctuations; fALFF) in 59 healthy children aged 7–18 years, and examined relationships between modalities. Principal components analysis (PCA) was applied to each modality in parallel, and participant scores for the top components were assessed for age associations. We found that decompositions of CBF, GMV and fALFF all included components for which scores were significantly associated with age. The dominant patterns in GMV and CBF showed significant (GMV) or trend level (CBF) associations with age and a strong spatial overlap, driven by increased signal intensity in default mode network (DMN) regions. GMV, CBF and fALFF additionally showed components accounting for 3–5% of variability with significant age associations. However, these patterns were relatively spatially independent, with small‐to‐moderate overlap between modalities. Independence of age effects was further demonstrated by correlating individual subject maps between modalities: CBF was significantly less correlated with GMV and fALFF in older children relative to younger. These spatially independent effects of age suggest that the parallel decline observed in global GMV and CBF may not reflect spatially synchronized processes. Hum Brain Mapp 38:2398–2407, 2017. © 2017 Wiley Periodicals, Inc.