Anatomical variability in the cortical representation of first and second language

The Impact of Diglossia on Executive Functions and on Reading in Arabic

BACKGROUND

In contrast to most other languages, where the spoken and written words are similar, children that have mastered Spoken Arabic (SA) learn to read a new written form of Arabic usually called Literary Arabic (LA). This phenomenon is called "diglossia".

METHODS

Based on a series of studies comparing monolingual Arabic speaking and bilingual children, it has been suggested that Arabic speaking individuals develop metacognitive abilities that are considered bilinguals de facto. Some of the cognitive functions that would seem to benefit from fluency in more than one language are metalinguistic and metacognitive awareness.

RESULTS

This review article summarizes the results of studies on the relationship between bilingualism, diglossia and executive functions (EFs) which involve metacognitive awareness, selective attention, control of inhibition and cognitive flexibility as well as working memory (phonemic manipulation and metalingual performances).

CONCLUSIONS

The findings are in line with research results that have shown that bilingualism has a positive effect on the functioning of an individual's attentional system across the lifespan. The neural basis of diglossia in Arabic, as well as the conclusions and implications drawn from the impact of diglossia on EF and on reading in Arabic, are discussed.

Distinct functional connectivity patterns during naturalistic learning by adolescent first versus second language speakers

Spoken lessons (lectures) are commonly used in schools as a medium for conveying educational content. In adolescence, experience-expectant maturation of language and cognitive systems supports learning; however, little is known about whether or how learners' language experiences interact with this integration process during learning. We examined functional connectivity using fMRI in 38 Spanish-English bilingual (L1-Spanish) and English monolingual (L1-English) adolescents during a naturalistic science video lesson in English. Seed analyses including the left inferior frontal gyrus (pars opercularis) and posterior middle temporal gyrus showed that L1-Spanish adolescents, when learning in their second language (L2), displayed widespread bilateral functional connectivity throughout the cortex while L1-English adolescents displayed mostly left-lateralized connectivity with core language regions over the course of the science lesson. Furthermore, we identified functional seed connectivity associated with better learning outcomes for adolescents with diverse language backgrounds. Importantly, functional connectivity patterns in L1-Spanish adolescents while learning in English also correlate with their Spanish cloze reading. Findings suggest that functional networks associated with higher-order language processing and cognitive control are differentially engaged for L1 vs. L2 speakers while learning new information through spoken language.

Original language versus dubbed movies: Effects on our brain and emotions

Converging evidence suggests that emotions are often dulled in one's foreign language. Here, we paired fMRI with a naturalistic viewing paradigm (i.e., original vs. dubbed versions of sad, fun and neutral movie clips) to investigate the neural correlates of emotion perception as a function of native (L1) and foreign (L2) language context. Watching emotional clips in L1 (vs. L2) reflected in activations of anterior temporal cortices involved in semantic cognition, arguably indicating a closer association of emotion concepts with the native language. The processing of fun clips in L1 (vs. L2) reflected in enhanced response of the right amygdala, suggesting a deeper emotional experience of positively valenced stimuli in the L1. Of interest, the amygdala response to fun clips positively correlated with participants' proficiency in the L2, indicating that a higher L2 competence may reduce emotional processing differences across a bilingual's two languages. Our findings are compatible with the view that language provides a context for the construction of emotions.

The Role of Letter-Speech Sound Integration in Native and Second Language Reading: A Study in Native Japanese Readers Learning English

The automatic activation of letter-speech sound (L-SS) associations is a vital step in typical reading acquisition. However, the contribution of L-SS integration during nonalphabetic native and alphabetic second language (L2) reading remains unclear. This study explored whether L-SS integration plays a similar role in a nonalphabetic language as in alphabetic languages and its contribution to L2 reading among native Japanese-speaking adults with varying English proficiency. A priming paradigm in Japanese and English was performed by presenting visual letters or symbols, followed by auditory sounds. We compared behavioral and event-related responses elicited by congruent letter-sound pairs, incongruent pairs, and baseline condition (symbol-sound pairs). The behavioral experiment revealed shorter RTs in the congruent condition for Japanese and English tasks, suggesting a facilitation effect of congruency. The ERP experiment results showed an increased early N1 response to Japanese congruent pairs compared to corresponding incongruent stimuli at the left frontotemporal electrodes. Interestingly, advanced English learners exhibited greater activities in bilateral but predominantly right-lateralized frontotemporal regions for the congruent condition within the N1 time window. Moreover, the enhancement of P2 response to congruent pairs was observed in intermediate English learners. These findings indicate that, despite deviations from native language processing, advanced speakers may successfully integrate letters and sounds during English reading, whereas intermediate learners may encounter difficulty in achieving L-SS integration when reading L2. Furthermore, our results suggest that L2 proficiency may affect the level of automaticity in L-SS integration, with the right P2 congruency effect playing a compensatory role for intermediate learners.

Functional characterization of the language network of polyglots and hyperpolyglots with precision fMRI

How do polyglots-individuals who speak five or more languages-process their languages, and what can this population tell us about the language system? Using fMRI, we identified the language network in each of 34 polyglots (including 16 hyperpolyglots with knowledge of 10+ languages) and examined its response to the native language, non-native languages of varying proficiency, and unfamiliar languages. All language conditions engaged all areas of the language network relative to a control condition. Languages that participants rated as higher proficiency elicited stronger responses, except for the native language, which elicited a similar or lower response than a non-native language of similar proficiency. Furthermore, unfamiliar languages that were typologically related to the participants' high-to-moderate-proficiency languages elicited a stronger response than unfamiliar unrelated languages. The results suggest that the language network's response magnitude scales with the degree of engagement of linguistic computations (e.g. related to lexical access and syntactic-structure building). We also replicated a prior finding of weaker responses to native language in polyglots than non-polyglot bilinguals. These results contribute to our understanding of how multiple languages coexist within a single brain and provide new evidence that the language network responds more strongly to stimuli that more fully engage linguistic computations.

Functional characterization of the language network of polyglots and hyperpolyglots with precision fMRI

How do polyglots-individuals who speak five or more languages-process their languages, and what can this population tell us about the language system? Using fMRI, we identified the language network in each of 34 polyglots (including 16 hyperpolyglots with knowledge of 10+ languages) and examined its response to the native language, non-native languages of varying proficiency, and unfamiliar languages. All language conditions engaged all areas of the language network relative to a control condition. Languages that participants rated as higher-proficiency elicited stronger responses, except for the native language, which elicited a similar or lower response than a non-native language of similar proficiency. Furthermore, unfamiliar languages that were typologically related to the participants' high-to-moderate-proficiency languages elicited a stronger response than unfamiliar unrelated languages. The results suggest that the language network's response magnitude scales with the degree of engagement of linguistic computations (e.g., related to lexical access and syntactic-structure building). We also replicated a prior finding of weaker responses to native language in polyglots than non-polyglot bilinguals. These results contribute to our understanding of how multiple languages co-exist within a single brain and provide new evidence that the language network responds more strongly to stimuli that more fully engage linguistic computations.

The right superior temporal gyrus plays a role in semantic-rule learning: Evidence supporting a reinforcement learning model

In real-life communication, individuals use language that carries evident rewarding and punishing elements, such as praise and criticism. A common trend is to seek more praise while avoiding criticism. Furthermore, semantics is crucial for conveying information, but such semantic access to native and foreign languages is subtly distinct. To investigate how rule learning occurs in different languages and to highlight the importance of semantics in this process, we investigated both verbal and non-verbal rule learning in first (L1) and second (L2) languages using a reinforcement learning framework, including a semantic rule and a color rule. Our computational modeling on behavioral and brain imaging data revealed that individuals may be more motivated to learn and adhere to rules in an L1 compared to L2, with greater striatum activation during the outcome phase in the L1. Additionally, results on the learning rates and inverse temperature in the two rule learning tasks showed that individuals tend to be conservative and are reluctant to change their judgments regarding rule learning of semantic information. Moreover, the greater the prediction errors, the greater activation of the right superior temporal gyrus in the semantic-rule learning condition, demonstrating that such learning has differential neural correlates than symbolic rule learning. Overall, the findings provide insight into the neural mechanisms underlying rule learning in different languages, and indicate that rule learning involving verbal semantics is not a general symbolic learning that resembles a conditioned stimulus-response, but rather has its own specific characteristics.

A systematic review of neuroimaging approaches to mapping language in individuals

Although researchers often rely on group-level fMRI results to draw conclusions about the neurobiology of language, doing so without accounting for the complexities of individual brains may reduce the validity of our findings. Furthermore, understanding brain organization in individuals is critically important for both basic science and clinical translation. To assess the state of single-subject language localization in the functional neuroimaging literature, we carried out a systematic review of studies published through April 2020. Out of 977 papers identified through our search, 121 met our inclusion criteria for reporting single-subject fMRI results (fMRI studies of language in adults that report task-based single-subject statistics). Of these, 20 papers reported using a single-subject test-retest analysis to assess reliability. Thus, we found that a relatively modest number of papers reporting single-subject results quantified single-subject reliability. These varied substantially in acquisition parameters, task design, and reliability measures, creating significant challenges for making comparisons across studies. Future endeavors to optimize the localization of language networks in individuals will benefit from the standardization and broader reporting of reliability metrics for different tasks and acquisition parameters.

Cortical Location of Language Function May Differ between Languages While White Matter Pathways Are Similar in Brain Lesion Patients

The neural representation of language can be identified cortically using navigated repetitive transcranial magnetic stimulation and subcortically using the fiber tracking of diffusion tensor imaging. We investigated how cortical locations of language and language-eloquent white matter pathways differ in 40 brain lesion patients speaking various languages. Error rates related to stimulations at single sites in the frontal and parietal lobe differed significantly between Balto-Slavic and Indo-European languages. Error rates related to stimulations at single sites in the temporal lobe differed significantly between bilingual individuals. No differences were found in the white matter language pathway volumes between Balto-Slavic and Indo-European languages nor between bilingual patients. These original and exploratory data indicate that the underlying subcortical structure might be similar across languages, with initially observed differences in the cortical location of language depending on the semantic processing, but these could not be confirmed using detailed statistical analyses pointing at a similar cortical and subcortical network.

Neural signatures of second language proficiency in narrative processing

Making sense of speech in a second language relies on multiple abilities. Differences in brain activity related to proficiency in language tasks have often been attributed to processing demands. However, during naturalistic narrative comprehension, listeners at different proficiency levels may form different representations of the same speech. We hypothesized that the intersubject synchronization of these representations could be used to measure second-language proficiency. Using a searchlight-shared response model, we found highly proficient participants showed synchronization in regions similar to those of native speakers, including in the default mode network and the lateral prefrontal cortex. In contrast, participants with low proficiency showed more synchronization in auditory cortex and word-level semantic processing areas in the temporal lobe. Moderate proficiency showed the greatest neural diversity, suggesting lower consistency in the source of this partial proficiency. Based on these synchronization differences, we were able to classify the proficiency level or predict behavioral performance on an independent English test in held-out participants, suggesting the identified neural systems represented proficiency-sensitive information that was generalizable to other individuals. These findings suggest higher second-language proficiency leads to more native-like neural processing of naturalistic language, including in systems beyond the cognitive control network or the core language network.

Tracing development of song memory with fMRI in zebra finches after a second tutoring experience

Sensory experiences in early development shape higher cognitive functions such as language acquisition in humans and song learning in birds. Zebra finches (Taeniopygia guttata) sequentially exposed to two different song 'tutors' during the sensitive period in development are able to learn from their second tutor and eventually imitate aspects of his song, but the neural substrate involved in learning a second song is unknown. We used fMRI to examine neural activity associated with learning two songs sequentially. We found that acquisition of a second song changes lateralization of the auditory midbrain. Interestingly, activity in the caudolateral Nidopallium (NCL), a region adjacent to the secondary auditory cortex, was related to the fidelity of second-song imitation. These findings demonstrate that experience with a second tutor can permanently alter neural activity in brain regions involved in auditory perception and song learning.

White matter brain structure predicts language performance and learning success

Individual differences in the ability to process language have long been discussed. Much of the neural basis of these, however, is yet unknown. Here we investigated the relationship between long-range white matter connectivity of the brain, as revealed by diffusion tractography, and the ability to process syntactically complex sentences in the participants' native language as well as the improvement thereof by multiday training. We identified specific network motifs by singular value decomposition that indeed related white matter structural connectivity to individual language processing performance. First, for two such motifs, one in the left and one in the right hemisphere, their individual prevalence significantly predicted the individual language performance, suggesting an anatomical predisposition for the individual ability to process syntactically complex sentences. Both motifs comprise a number of cortical regions, but seem to be dominated by areas known for the involvement in working memory rather than the classical language network itself. Second, we identified another left hemispheric network motif, whose change of prevalence over the training period significantly correlated with the individual change in performance, thus reflecting training induced white matter plasticity. This motif comprises diverse cortical areas including regions known for their involvement in language processing, working memory and motor functions. The present findings suggest that individual differences in language processing and learning can be explained, in part, by individual differences in the brain's white matter structure. Brain structure may be a crucial factor to be considered when discussing variations in human cognitive performance, more generally.

Preoperative function-specific connectome analysis predicts surgery-related aphasia after glioma resection

Glioma resection within language-eloquent regions poses a high risk of surgery-related aphasia (SRA). Preoperative functional mapping by navigated transcranial magnetic stimulation (nTMS) combined with diffusion tensor imaging (DTI) is increasingly used to localize cortical and subcortical language-eloquent areas. This study enrolled 60 nonaphasic patients with left hemispheric perisylvian gliomas to investigate the prediction of SRA based on function-specific connectome network properties under different fractional anisotropy (FA) thresholds. Moreover, we applied a machine learning model for training and cross-validation to predict SRA based on preoperative connectome parameters. Preoperative connectome analysis helps predict SRA development with an accuracy of 73.3% and sensitivity of 78.3%. The current study provides a new perspective of combining nTMS and function-specific connectome analysis applied in a machine learning model to investigate language in neurooncological patients and promises to advance our understanding of the intricate networks.

Left and Right Arcuate Fasciculi Are Uniquely Related to Word Reading Skills in Chinese-English Bilingual Children

Whether reading in different writing systems recruits language-unique or language-universal neural processes is a long-standing debate. Many studies have shown the left arcuate fasciculus (AF) to be involved in phonological and reading processes. In contrast, little is known about the role of the right AF in reading, but some have suggested that it may play a role in visual spatial aspects of reading or the prosodic components of language. The right AF may be more important for reading in Chinese due to its logographic and tonal properties, but this hypothesis has yet to be tested. We recruited a group of Chinese-English bilingual children (8.2 to 12.0 years old) to explore the common and unique relation of reading skill in English and Chinese to fractional anisotropy (FA) in the bilateral AF. We found that both English and Chinese reading skills were positively correlated with FA in the rostral part of the left AF-direct segment. Additionally, English reading skill was positively correlated with FA in the caudal part of the left AF-direct segment, which was also positively correlated with phonological awareness. In contrast, Chinese reading skill was positively correlated with FA in certain segments of the right AF, which was positively correlated with visual spatial ability, but not tone discrimination ability. Our results suggest that there are language universal substrates of reading across languages, but that certain left AF nodes support phonological mechanisms important for reading in English, whereas certain right AF nodes support visual spatial mechanisms important for reading in Chinese.

An Event-Related Potentials Study on the Syntactic Transfer Effect of Late Language Learners

This study explored the syntactic transfer effect of the non-local subject-verb agreement structure with plural head noun after two intensive phases of input training with event-related potentials (ERP). The non-local subject-verb agreement stimuli with the plural head nouns, which never appeared in training phases, were used for the stimuli. A total of 26 late L1-Chinese L2-English learners, who began to learn English after a critical period and participated in our previous experiments, were asked back to take part in this syntactic transfer experiment. Results indicated that a significant ERP component P600 occurred in the key region (the verb) of the sentences with syntactic violations in the experimental group, but none occurred in the control group. This demonstrated that there was a significant transfer effect of the input training. The possible theoretical explanation was provided and also the malleability of the late L2 learners was discussed.

Subject–Verb Number Agreement in Bilingual Processing: (Lack of) Age of Acquisition and Proficiency Effects

Children acquire language more easily than adults, though it is controversial whether this faculty declines as a result of a critical period or something else. To address this question, we investigate the role of age of acquisition and proficiency on morphosyntactic processing in adult monolinguals and bilinguals. Spanish monolinguals and intermediate and advanced early and late bilinguals of Spanish read sentences with adjacent subject–verb number agreements and violations and chose one of four pictures. Eye-tracking data revealed that all groups were sensitive to the violations and attended more to more salient plural and preterit verbs than less obvious singular and present verbs, regardless of AoA and proficiency level. We conclude that the processing of adjacent SV agreement depends on perceptual salience and language use, rather than AoA or proficiency. These findings support usage-based theories of language acquisition.

Vocal Learning and Behaviors in Birds and Human Bilinguals: Parallels, Divergences and Directions for Research

Comparisons between the communication systems of humans and animals are instrumental in contextualizing speech and language into an evolutionary and biological framework and for illuminating mechanisms of human communication. As a complement to previous work that compares developmental vocal learning and use among humans and songbirds, in this article we highlight phenomena associated with vocal learning subsequent to the development of primary vocalizations (i.e., the primary language (L1) in humans and the primary song (S1) in songbirds). By framing avian “second-song” (S2) learning and use within the human second-language (L2) context, we lay the groundwork for a scientifically-rich dialogue between disciplines. We begin by summarizing basic birdsong research, focusing on how songs are learned and on constraints on learning. We then consider commonalities in vocal learning across humans and birds, in particular the timing and neural mechanisms of learning, variability of input, and variability of outcomes. For S2 and L2 learning outcomes, we address the respective roles of age, entrenchment, and social interactions. We proceed to orient current and future birdsong inquiry around foundational features of human bilingualism: L1 effects on the L2, L1 attrition, and L1<–>L2 switching. Throughout, we highlight characteristics that are shared across species as well as the need for caution in interpreting birdsong research. Thus, from multiple instructive perspectives, our interdisciplinary dialogue sheds light on biological and experiential principles of L2 acquisition that are informed by birdsong research, and leverages well-studied characteristics of bilingualism in order to clarify, contextualize, and further explore S2 learning and use in songbirds.

Accent discrimination abilities during the first days of life: An fNIRS study

Humans are biologically endowed with the faculty of language. However, the way neonates can crack this complex communicative code is yet not totally understood. While phonetic discrimination has been widely investigated in neonates, less is known about the role of supra-segments patterns in the recognition of native language. Therefore, the aim of this study was to evaluate accent discrimination abilities in newborns in a sentential prosody paradigm. We used near-infared spectroscopy to investigate accent discrimination in 21 full-term born infants within the first days of life. Sentential prosody was used to investigate: (a) native accent, (b) foreign accent, and (c) flattened accent. Neonates revealed a significantly smaller hemodynamic response to native accent compared to flattened accent and foreign accent, respectively. Cluster-based permutation analysis revealed two clusters with a significant difference between the two conditions native accent and foreign accent. The first cluster covered the middle and superior frontal, middle and superior temporal, central, and parietal areas within the left hemisphere. The second cluster, located in the right hemisphere, covered inferior, middle, and superior frontal, central, middle and superior temporal areas. We therefore conclude that neonates can differentiate prosodic features like accents within the same language a few days after birth.

Cerebral lateralisation of first and second languages in bilinguals assessed using functional transcranial Doppler ultrasound

Background: Lateralised language processing is a well-established finding in monolinguals. In bilinguals, studies using fMRI have typically found substantial regional overlap between the two languages, though results may be influenced by factors such as proficiency, age of acquisition and exposure to the second language. Few studies have focused specifically on individual differences in brain lateralisation, and those that have suggested reduced lateralisation may characterise representation of the second language (L2) in some bilingual individuals.

Methods: In Study 1, we used functional transcranial Doppler sonography (FTCD) to measure cerebral lateralisation in both languages in high proficiency bilinguals who varied in age of acquisition (AoA) of L2. They had German (N = 14) or French (N = 10) as their first language (L1) and English as their second language. FTCD was used to measure task-dependent blood flow velocity changes in the left and right middle cerebral arteries during phonological word generation cued by single letters. Language history measures and handedness were assessed through self-report. Study 2 followed a similar format with 25 Japanese (L1) /English (L2) bilinguals, with proficiency in their second language ranging from basic to advanced, using phonological and semantic word generation tasks with overt speech production.

Results: In Study 1, participants were significantly left lateralised for both L1 and L2, with a high correlation (r = .70) in the size of laterality indices for L1 and L2. In Study 2, again there was good agreement between LIs for the two languages (r = .77 for both word generation tasks). There was no evidence in either study of an effect of age of acquisition, though the sample sizes were too small to detect any but large effects. 

Conclusion: In proficient bilinguals, there is strong concordance for cerebral lateralisation of first and second language as assessed by a verbal fluency task.

What Can Glioma Patients Teach Us about Language (Re)Organization in the Bilingual Brain: Evidence from fMRI and MEG

Recent evidence suggests that the presence of brain tumors (e.g., low-grade gliomas) triggers language reorganization. Neuroplasticity mechanisms called into play can transfer linguistic functions from damaged to healthy areas unaffected by the tumor. This phenomenon has been reported in monolingual patients, but much less is known about the neuroplasticity of language in the bilingual brain. A central question is whether processing a first or second language involves the same or different cortical territories and whether damage results in diverse recovery patterns depending on the language involved. This question becomes critical for preserving language areas in bilingual brain-tumor patients to prevent involuntary pathological symptoms following resection. While most studies have focused on intraoperative mapping, here, we go further, reporting clinical cases for five bilingual patients tested before and after tumor resection, using a novel multimethod approach merging neuroimaging information from fMRI and MEG to map the longitudinal reshaping of the language system. Here, we present four main findings. First, all patients preserved linguistic function in both languages after surgery, suggesting that the surgical intervention with intraoperative language mapping was successful in preserving cortical and subcortical structures necessary for brain plasticity at the functional level. Second, we found reorganization of the language network after tumor resection in both languages, mainly reflected by a shift of activity to right hemisphere nodes and the recruitment of ipsilesional left nodes. Third, we found that this reorganization varied according to the language involved, indicating that L1 and L2 follow different reshaping patterns after surgery. Fourth, oscillatory longitudinal effects were correlated with BOLD laterality changes in superior parietal and middle frontal areas. These findings may reflect that neuroplasticity impacts on the compensatory involvement of executive control regions, supporting the allocation of cognitive resources as a consequence of increased attentional demands. Furthermore, these results hint at the complementary role of this neuroimaging approach in language mapping, with fMRI offering excellent spatial localization and MEG providing optimal spectrotemporal resolution.

The cortical distribution of first and second language in the right hemisphere of bilinguals - an exploratory study by repetitive navigated transcranial magnetic stimulation

First language (L1) and second language (L2) processing in bilinguals is not yet fully understood, especially not when considering the non-dominant hemisphere. Ten healthy, right-handed volunteers underwent language mapping of the right hemisphere by repetitive navigated transcranial magnetic stimulation and an object-naming task in their L1 and L2. All elicited naming errors together, no responses, and all errors without hesitation were analyzed separately for cortical distributions of error rates (ERs: number of errors divided by the number of applied stimulations). No significant differences (p > 0.05) were found in ERs between the L1 and L2 for all errors (L1 20.6 ± 14.8%, L2 15.4 ± 11.2%), no responses (L1 13.5 ± 10.9%, L2 9.2 ± 10.8%), and all errors without hesitation (L1 14.4 ± 11.2%, L2 10.8 ± 10.0%). The areas that showed high ERs for the L1 included the dorsal precentral and middle precentral gyrus, whereas the triangular inferior frontal gyrus showed high ERs for the L2. When focusing on error distributions per single stimulation points, differences in ERs between the L1 and L2 were initially observed for stimulation within the angular and middle middle frontal gyrus, but did not withstand correction for the false discovery rate (FDR-corrected p > 0.05). In conclusion, this exploratory study shows the feasibility of rTMS to the right hemisphere for language mapping and reveals cortical areas involved in L1 and L2 processing, but has to be followed up by larger studies enrolling more homogeneous cohorts.

Chinese-English bilinguals show linguistic-perceptual links in the brain associating short spoken phrases with corresponding real-world natural action sounds by semantic category

Higher cognitive functions such as linguistic comprehension must ultimately relate to perceptual systems in the brain, though how and why this forms remains unclear. Different brain networks that mediate perception when hearing real-world natural sounds has recently been proposed to respect a taxonomic model of acoustic-semantic categories. Using functional magnetic resonance imaging (fMRI) with Chinese/English bilingual listeners, the present study explored whether reception of short spoken phrases, in both Chinese (Mandarin) and English, describing corresponding sound-producing events would engage overlapping brain regions at a semantic category level. The results revealed a double-dissociation of cortical regions that were preferential for representing knowledge of human versus environmental action events, whether conveyed through natural sounds or the corresponding spoken phrases depicted by either language. These findings of cortical hubs exhibiting linguistic-perceptual knowledge links at a semantic category level should help to advance neurocomputational models of the neurodevelopment of language systems.

Using magnetoencephalography to examine word recognition, lateralization, and future language skills in 14-month-old infants

Word learning is a significant milestone in language acquisition. The second year of life marks a period of dramatic advances in infants' expressive and receptive word-processing abilities. Studies show that in adulthood, language processing is left-hemisphere dominant. However, adults learning a second language activate right-hemisphere brain functions. In infancy, acquisition of a first language involves recruitment of bilateral brain networks, and strong left-hemisphere dominance emerges by the third year. In the current study we focus on 14-month-old infants in the earliest stages of word learning using infant magnetoencephalography (MEG) brain imagining to characterize neural activity in response to familiar and unfamiliar words. Specifically, we examine the relationship between right-hemisphere brain responses and prospective measures of vocabulary growth. As expected, MEG source modeling revealed a broadly distributed network in frontal, temporal and parietal cortex that distinguished word classes between 150-900 ms after word onset. Importantly, brain activity in the right frontal cortex in response to familiar words was highly correlated with vocabulary growth at 18, 21, 24, and 27 months. Specifically, higher activation to familiar words in the 150-300 ms interval was associated with faster vocabulary growth, reflecting processing efficiency, whereas higher activation to familiar words in the 600-900 ms interval was associated with slower vocabulary growth, reflecting cognitive effort. These findings inform research and theory on the involvement of right frontal cortex in specific cognitive processes and individual differences related to attention that may play an important role in the development of left-lateralized word processing.

Converging Evidence for Differential Specialization and Plasticity of Language Systems

Functional specialization and plasticity are fundamental organizing principles of the brain. Since the mid-1800s, certain cognitive functions have been known to be lateralized, but the provenance and flexibility of hemispheric specialization remain open questions. Language is a uniquely human phenomenon that requires a delicate balance between neural specialization and plasticity, and language learning offers the perfect window to study these principles in the human brain. In the current study, we conducted two separate functional MRI experiments with language learners (male and female), one cross-sectional and one longitudinal, involving distinct populations and languages, and examined hemispheric lateralization and learning-dependent plasticity of the following three language systems: reading, speech comprehension, and verbal production. A multipronged analytic approach revealed a highly consistent pattern of results across the two experiments, showing (1) that in both native and non-native languages, while language production was left lateralized, lateralization for language comprehension was highly variable across individuals; and (2) that with increasing non-native language proficiency, reading and speech comprehension displayed substantial changes in hemispheric dominance, with languages tending to lateralize to opposite hemispheres, while production showed negligible change and remained left lateralized. These convergent results shed light on the long-standing debate of neural organization of language by establishing robust principles of lateralization and plasticity of the main language systems. Findings further suggest involvement of the sensorimotor systems in language lateralization and its plasticity.SIGNIFICANCE STATEMENT The human brain exhibits a remarkable ability to support a vast variety of languages that may be acquired at different points in the life span. Language is a complex construct involving linguistic as well as visual, auditory, and motor processes. Using functional MRI, we examined hemispheric specialization and learning-dependent plasticity of three language systems-reading, speech comprehension, and verbal production-in cross-sectional and longitudinal experiments in language learners. A multipronged analytic approach revealed converging evidence for striking differences in hemispheric specialization and plasticity among the language systems. The results have major theoretical and practical implications for our understanding of fundamental principles of neural organization of language, language testing and recovery in patients, and language learning in healthy populations.

Word learning in two languages: Neural overlap and representational differences

We investigated the neural basis of newly learned words in Spanish as a mother tongue (L1) and English as a second language (L2). Participants acquired new names for real but unfamiliar concepts in both languages over the course of two days. On day 3, they completed a semantic categorization task during fMRI scanning. The results revealed largely overlapping brain regions for newly learned words in Spanish and English. However, Spanish showed a heightened BOLD response within prefrontal cortex (PFC), due to increased competition of existing lexical representations. In contrast, English displayed higher activity than Spanish within primary auditory cortex, which suggests increased phonological processing due to more irregular phonological-orthographic mappings. Overall, these results suggest that novel words are learned similarly in Spanish L1 and English L2, and that they are represented in largely overlapping brain regions. However, they differ in terms of cognitive control and phonological processes.

Converging Evidence for Differential Specialization and Plasticity of Language Systems

Functional specialization and plasticity are fundamental organizing principles of the brain. Since the mid-1800s, certain cognitive functions have been known to be lateralized, but the provenance and flexibility of hemispheric specialization remain open questions. Language is a uniquely human phenomenon that requires a delicate balance between neural specialization and plasticity, and language learning offers the perfect window to study these principles in the human brain. In the current study, we conducted two separate functional MRI experiments with language learners (male and female), one cross-sectional and one longitudinal, involving distinct populations and languages, and examined hemispheric lateralization and learning-dependent plasticity of the following three language systems: reading, speech comprehension, and verbal production. A multipronged analytic approach revealed a highly consistent pattern of results across the two experiments, showing (1) that in both native and non-native languages, while language production was left lateralized, lateralization for language comprehension was highly variable across individuals; and (2) that with increasing non-native language proficiency, reading and speech comprehension displayed substantial changes in hemispheric dominance, with languages tending to lateralize to opposite hemispheres, while production showed negligible change and remained left lateralized. These convergent results shed light on the long-standing debate of neural organization of language by establishing robust principles of lateralization and plasticity of the main language systems. Findings further suggest involvement of the sensorimotor systems in language lateralization and its plasticity.

SIGNIFICANCE STATEMENT The human brain exhibits a remarkable ability to support a vast variety of languages that may be acquired at different points in the life span. Language is a complex construct involving linguistic as well as visual, auditory, and motor processes. Using functional MRI, we examined hemispheric specialization and learning-dependent plasticity of three language systems—reading, speech comprehension, and verbal production—in cross-sectional and longitudinal experiments in language learners. A multipronged analytic approach revealed converging evidence for striking differences in hemispheric specialization and plasticity among the language systems. The results have major theoretical and practical implications for our understanding of fundamental principles of neural organization of language, language testing and recovery in patients, and language learning in healthy populations.

Selective aphasia and focal hypoperfusion in a bilingual patient with HaNDL syndrome

The syndrome of transient headache and neurological deficits with cerebrospinal fluid lymphocytosis (HaNDL) is a rare disease (1) characterized by a benign, self-limited headache syndrome accompanied by neurological deficits (isolated aphasia can be seen in nearly 22% of these patients (2)). Differential diagnosis between acute ischemic stroke and HaNDL syndrome has to be made in order to decide whether to perform a lumbar puncture or start reperfusion treatment early. CT perfusion have proved to be useful for differential diagnosis (3). We present a case of a HaNDL patient referred to the Emergency Department as a stroke in the context of acute onset of selective aphasia (Spanish) in a bilingual patient (French-Spanish). Urgent CT perfusion during the episode revealed increased mean transit time (MTT) with normal Cerebral Blood Flow (CBF) in posterior language areas. The case provides information on a HaNDL attack and its pathophysiology with hemodynamic changes in the acute period during the episode and the benign condition of the illness.

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Headache and Neurological Deficits with Cerebrospinal Fluid Lymphocytosis (HaNDL) syndrome is a benign and self-limiting clinical condition

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Differential diagnosis is a challenging scenario in the acute setting.

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Migraine, stroke, meningoencephalitis or seizures should be considered.

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Blood flow changes during a HaNDL episode supports common pathophysiological denominator between migraine with aura and HaNDLsyndrome.

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The case supports the hypothesis that locus for a language learned in later stages is located in an area different from that for the native language.

Differential Neurobehavioral Effects of Cross-Modal Selective Priming on Phonetic and Emotional Prosodic Information in Late Second Language Learners

Purpose Spoken language is inherently multimodal and multidimensional in natural settings, but very little is known about how second language (L2) learners undertake multilayered speech signals with both phonetic and affective cues. This study investigated how late L2 learners undertake parallel processing of linguistic and affective information in the speech signal at behavioral and neurophysiological levels. Method Behavioral and event-related potential measures were taken in a selective cross-modal priming paradigm to examine how late L2 learners (N = 24, M _age = 25.54 years) assessed the congruency of phonetic (target vowel: /a/ or /i/) and emotional (target affect: happy or angry) information between the visual primes of facial pictures and the auditory targets of spoken syllables. Results Behavioral accuracy data showed a significant congruency effect in affective (but not phonetic) priming. Unlike a previous report on monolingual first language (L1) users, the L2 users showed no facilitation in reaction time for congruency detection in either selective priming task. The neurophysiological results revealed a robust N400 response that was stronger in the phonetic condition but without clear lateralization and that the N400 effect was weaker in late L2 listeners than in monolingual L1 listeners. Following the N400, late L2 learners showed a weaker late positive response than the monolingual L1 users, particularly in the left central to posterior electrode regions. Conclusions The results demonstrate distinct patterns of behavioral and neural processing of phonetic and affective information in L2 speech with reduced neural representations in both the N400 and the later processing stage, and they provide an impetus for further research on similarities and differences in L1 and L2 multisensory speech perception in bilingualism.

Clinical Utility of Preoperative Bilingual Language fMRI Mapping in Patients with Brain Tumors

BACKGROUND AND PURPOSE

Previous literature has demonstrated disparity in the postoperative recovery of first and second language function of bilingual neurosurgical patients. However, it is unclear to whether preoperative brain mapping of both languages is needed. In this study, we aimed to evaluate the clinical utility of language task functional MRI (fMRI) implemented in both languages in bilingual patients.

METHODS

We retrospectively examined fMRI data of 13 bilingual brain tumor patients (age: 23 to 59 years) who performed antonym generation task-based fMRIs in English and non-English language. The usefulness of bilingual language mapping was evaluated using a structured survey administered to 5 neurosurgeons. Additionally, quantitative comparison between the brain activation maps of both languages was performed.

RESULTS

Survey responses revealed differences in raters' surgical approach, including asleep versus awake surgery and extent of resection, after viewing the language fMRI maps. Additional non-English fMRI led to changes in surgical decision-making and bettered localization of language areas. Quantitative analysis revealed an increase in laterality index (LI) in non-English fMRI compared to English fMRI. The Dice coefficient demonstrated fair overlap (.458 ± .160) between the activation maps.

CONCLUSION

Bilingual fMRI mapping of bilingual patients allows to better appreciate functionally active language areas that may be neglected in single language mapping. Utility of bilingual mapping was supported by changes in both surgical approach and LI measurements, suggesting its benefit on preoperative language mapping.

Functional plasticity associated with language learning in adults

Learning a new language in adulthood is increasingly common and among the most difficult tasks attempted by adults. Adult language learners thus offer an excellent window into the nature of learning-dependent plasticity. The present functional magnetic resonance imaging (fMRI) study was aimed at characterising functional neuroplasticity in adults at different stages of learning a second language (L2). To this end, a total of 34 adults, either intermediate or advanced L2 learners, underwent MRI scanning while performing a semantic judgement task with print and speech stimuli. Three separate analytical approaches were used to comprehensively map neural differences: print-speech convergence, L1-L2 similarity, and functional connectivity with language control regions. Results revealed that (i) print-speech convergence was not affected by L2 proficiency level, (ii) L1-L2 similarity was significantly higher in intermediate than in advanced L2 learners, and (iii) functional coupling of language and language control areas was higher in the advanced relative to the intermediate group during reading comprehension. The results point to significant functional differences between intermediate and advanced language learners, indicating that, even well into adulthood, increasing L2 proficiency modulates the functional similarity between L1 and L2 and the connectivity between language comprehension and language control regions, particularly in reading comprehension.

Neurological Aspects of Foreign Accent Syndrome in Stroke Patients

Foreign Accent Syndrome (FAS) is an intriguing motor speech disorder which has captured the interest of the scientific community and media for decades. At the moment, there is no comprehensive model which can account for the pathophysiology of this disorder. This paper presents a review of 112 FAS cases published between 1907 and October 2016: these were analyzed with respect to demographic characteristics, lesion location, associated neurocognitive symptoms, and comorbid speech and language disorders. The analysis revealed that organic-neurogenic FAS is more frequent in women than in men. In organic-neurogenic FAS over half of the patients acquired the foreign accent after a stroke. Their lesions are typically located in the left supratentorial regions of the brain, and generally involve the primary motor cortex and premotor cortex (BA 4 and 6), and/or the basal ganglia. Although neurocognitive data are not consistently reported, vascular FAS patients regularly suffer frontal executive dysfunctions. On the basis of a careful comparison of the cognitive and theoretical accounts of FAS, AoS and ataxic dysarthria, it is concluded that FAS should be regarded a dual component motor speech disorder in which both planning and motor execution of speech may be affected.

Rethinking the critical period for language: New insights into an old question from American Sign Language

The hypothesis that children surpass adults in long-term second-language proficiency is accepted as evidence for a critical period for language. However, the scope and nature of a critical period for language has been the subject of considerable debate. The controversy centers on whether the age-related decline in ultimate second-language proficiency is evidence for a critical period or something else. Here we argue that age-onset effects for first vs. second language outcome are largely different. We show this by examining psycholinguistic studies of ultimate attainment in L2 vs. L1 learners, longitudinal studies of adolescent L1 acquisition, and neurolinguistic studies of late L2 and L1 learners. This research indicates that L1 acquisition arises from post-natal brain development interacting with environmental linguistic experience. By contrast, L2 learning after early childhood is scaffolded by prior childhood L1 acquisition, both linguistically and neurally, making it a less clear test of the critical period for language.

Morpho-syntactic complexity modulates brain activation in Persian-English bilinguals: An fMRI study

The Persian language can be considered to have a relatively more complex and combinatorial morpho-syntax than languages like Chinese and English. For example, the Persian verbal system is largely constituted of light verb constructions, in which light verbs are combined with specific items coming from other grammatical classes to generate entirely new verbal entities. This study was designed to examine the mediating effect of language-inherent properties related to morpho-syntax on activation of the left inferior frontal gyrus (LIFG), a brain area involved in morpho-syntactic processing. To this end, 20 late Persian-English bilinguals were required to covertly generate verbs and nouns from object and action pictures, within a cued grammatical context. Consistent with predictions, the results of an ROI analysis revealed an interaction between task and language in BA 44 of the LIFG and its right homologue, with greater activation of this region during the production of Persian compared to English verbs. In contrast, there was greater activation of the BA 44 during the production of English compared to Persian nouns, consistent with the more effortful processing of their less proficient second language (English). The findings suggest that language-specific properties such as morpho-syntactic complexity can modulate the recruitment of Broca's area, over and above the more well-documented effects of language proficiency.

Functional Neuroanatomy of Second Language Sentence Comprehension: An fMRI Study of Late Learners of American Sign Language

The neurobiology of sentence comprehension is well-studied but the properties and characteristics of sentence processing networks remain unclear and highly debated. Sign languages (i.e., visual-manual languages), like spoken languages, have complex grammatical structures and thus can provide valuable insights into the specificity and function of brain regions supporting sentence comprehension. The present study aims to characterize how these well-studied spoken language networks can adapt in adults to be responsive to sign language sentences, which contain combinatorial semantic and syntactic visual-spatial linguistic information. Twenty native English-speaking undergraduates who had completed introductory American Sign Language (ASL) courses viewed videos of the following conditions during fMRI acquisition: signed sentences, signed word lists, English sentences and English word lists. Overall our results indicate that native language (L1) sentence processing resources are responsive to ASL sentence structures in late L2 learners, but that certain L1 sentence processing regions respond differently to L2 ASL sentences, likely due to the nature of their contribution to language comprehension. For example, L1 sentence regions in Broca's area were significantly more responsive to L2 than L1 sentences, supporting the hypothesis that Broca's area contributes to sentence comprehension as a cognitive resource when increased processing is required. Anterior temporal L1 sentence regions were sensitive to L2 ASL sentence structure, but demonstrated no significant differences in activation to L1 than L2, suggesting its contribution to sentence processing is modality-independent. Posterior superior temporal L1 sentence regions also responded to ASL sentence structure but were more activated by English than ASL sentences. An exploratory analysis of the neural correlates of L2 ASL proficiency indicates that ASL proficiency is positively correlated with increased activations in response to ASL sentences in L1 sentence processing regions. Overall these results suggest that well-established fronto-temporal spoken language networks involved in sentence processing exhibit functional plasticity with late L2 ASL exposure, and thus are adaptable to syntactic structures widely different than those in an individual's native language. Our findings also provide valuable insights into the unique contributions of the inferior frontal and superior temporal regions that are frequently implicated in sentence comprehension but whose exact roles remain highly debated.

Structural neural predictors of Farsi-English bilingualism

The neurobiology of bilingualism is hotly debated. The present study examines whether normalized cortical measurements can be used to reliably classify monolinguals versus bilinguals in a structural MRI dataset of Farsi-English bilinguals and English monolinguals. A decision tree classifier classified bilinguals with an average correct classification rate of 85%, and monolinguals with a rate of 71.4%. The most relevant regions for classification were the right supramarginal gyrus, left inferior temporal gyrus and left inferior frontal gyrus. Larger studies with carefully matched monolingual and bilingual samples are needed to confirm that features of these regions can reliably categorize monolingual and bilingual brains. Nonetheless, the present findings suggest that a single structural MRI scan, analyzed with measures readily available using default procedures in a free open-access software (Freesurfer), can be used to reliably predict an individual's language experience using a decision tree classifier, and that Farsi-English bilingualism implicates regions identified in previous group-level studies of bilingualism in other languages.

Identifying cortical first and second language sites via navigated transcranial magnetic stimulation of the left hemisphere in bilinguals

The cortical areas that code for the first (L1) and second language (L2) in bilinguals have still not been sufficiently explored. Thus, this study investigated the left-hemispheric distribution of the L1 and L2 using repetitive navigated transcranial magnetic stimulation (rTMS), in combination with an object-naming task, in 10 healthy, right-handed volunteers. In particular, higher error rates (ERs) were observed in the L1, and there was a statistically significant difference between the ERs of L1 and L2 for no-response errors (L1 mean 11.9±9.0%, L2 mean 6.5±5.2%; p=0.03). Furthermore, language-specific and shared cortical distribution patterns for the L1 and L2 were observed within the frontal, parietal, and temporal lobes with a trend towards higher occurrence of language-specific spots within posterior regions. Overall, the L1 presented a more stable pattern of language distribution compared to the L2.

The Neural Basis of Speech Perception through Lipreading and Manual Cues: Evidence from Deaf Native Users of Cued Speech

We present here the first neuroimaging data for perception of Cued Speech (CS) by deaf adults who are native users of CS. CS is a visual mode of communicating a spoken language through a set of manual cues which accompany lipreading and disambiguate it. With CS, sublexical units of the oral language are conveyed clearly and completely through the visual modality without requiring hearing. The comparison of neural processing of CS in deaf individuals with processing of audiovisual (AV) speech in normally hearing individuals represents a unique opportunity to explore the similarities and differences in neural processing of an oral language delivered in a visuo-manual vs. an AV modality. The study included deaf adult participants who were early CS users and native hearing users of French who process speech audiovisually. Words were presented in an event-related fMRI design. Three conditions were presented to each group of participants. The deaf participants saw CS words (manual + lipread), words presented as manual cues alone, and words presented to be lipread without manual cues. The hearing group saw AV spoken words, audio-alone and lipread-alone. Three findings are highlighted. First, the middle and superior temporal gyrus (excluding Heschl's gyrus) and left inferior frontal gyrus pars triangularis constituted a common, amodal neural basis for AV and CS perception. Second, integration was inferred in posterior parts of superior temporal sulcus for audio and lipread information in AV speech, but in the occipito-temporal junction, including MT/V5, for the manual cues and lipreading in CS. Third, the perception of manual cues showed a much greater overlap with the regions activated by CS (manual + lipreading) than lipreading alone did. This supports the notion that manual cues play a larger role than lipreading for CS processing. The present study contributes to a better understanding of the role of manual cues as support of visual speech perception in the framework of the multimodal nature of human communication.

fMRI Study of Sentence Generation by Early Bilinguals Differing in Proficiency Level

The aim of this study was to identify the functional anatomy of the cerebral speech regions involved in speaking in native and foreign language in the same subject using functional magnetic resonance imaging.

Experimental design consisted of two activation runs. Each of them included two kinds of tasks arranged in series of five blocks lasting for 30s. In the experimental condition of the first run subjects were required to speak in their native language and in the second run the task was to speak in the foreign language. In both runs, baseline condition was the same and subjects were supposed to lie silently inside the bore. We observed the influence of proficiency on brain activation. In subjects with equal proficiency in the first and the second language, differences were not observed. In the subjects with unequal proficiency in the first and the second language we observed two main effects.

First was difference in the strength and extension of activation, the second effect was activation of new regions for the second language, in which proficiency was lower.

Dichotic listening as an index of lateralization of speech perception in familial risk children with and without dyslexia

Atypical language lateralization has been marked as one of the factors that may contribute to the development of dyslexia. Indeed, atypical lateralization of linguistic functions such as speech processing in dyslexia has been demonstrated using neuroimaging studies, but also using the behavioral dichotic listening (DL) method. However, so far, DL results have been mixed. The current study assesses lateralization of speech processing by using DL in a sample of children at familial risk (FR) for dyslexia. In order to determine whether atypical lateralization of speech processing relates to reading ability, or is a correlate of being at familial risk, the current study compares the laterality index of FR children who did and did not become dyslexic, and a control group of readers without dyslexia. DL was tested in 3rd grade and in 5/6th grade. Results indicate that at both time points, all three groups have a right ear advantage, indicative of more pronounced left-hemispheric processing. However, the FR-dyslexic children are less good at reporting from the left ear than controls and FR-nondyslexic children. This impediment relates to reading fluency.

Age of language acquisition and cortical language organization in multilingual patients undergoing awake brain mapping

OBJECTIVE Most knowledge regarding the anatomical organization of multilingualism is based on aphasiology and functional imaging studies. However, the results have still to be validated by the gold standard approach, namely electrical stimulation mapping (ESM) during awake neurosurgical procedures. In this ESM study the authors describe language representation in a highly specific group of 13 multilingual individuals, focusing on how age of acquisition may influence the cortical organization of language. METHODS Thirteen patients who had a high degree of proficiency in multiple languages and were harboring lesions within the dominant, left hemisphere underwent ESM while being operated on under awake conditions. Demographic and language data were recorded in relation to age of language acquisition (for native languages and early- and late-acquired languages), neuropsychological pre- and postoperative language testing, the number and location of language sites, and overlapping distribution in terms of language acquisition time. Lesion growth patterns and histopathological characteristics, location, and size were also recorded. The distribution of language sites was analyzed with respect to age of acquisition and overlap. RESULTS The functional language-related sites were distributed in the frontal (55%), temporal (29%), and parietal lobes (16%). The total number of native language sites was 47. Early-acquired languages (including native languages) were represented in 97 sites (55 overlapped) and late-acquired languages in 70 sites (45 overlapped). The overlapping distribution was 20% for early-early, 71% for early-late, and 9% for late-late. The average lesion size (maximum diameter) was 3.3 cm. There were 5 fast-growing and 7 slow-growing lesions. CONCLUSIONS Cortical language distribution in multilingual patients is not homogeneous, and it is influenced by age of acquisition. Early-acquired languages have a greater cortical representation than languages acquired later. The prevalent native and early-acquired languages are largely represented within the perisylvian left hemisphere frontoparietotemporal areas, and the less prevalent late-acquired languages are mostly overlapped with them.