Convergent cortical representation of semantic processing in bilinguals

Language comprehension in the bilingual brain: fMRI and ERP support for psycholinguistic models

In this paper, we review issues in bilingual language comprehension in the light of functional magnetic resonance imaging (fMRI) and event-related brain potential (ERP) data. Next, we consider to what extent neuroimaging data are compatible with assumptions and characteristics of available psycholinguistic models of bilingual word processing, in particular the BIA+ model. We argue that this model provides a theoretical framework that is useful for interpreting both the spatial brain activation patterns observed with fMRI and the temporal brain wave patterns of ERP studies. Finally, we demonstrate that neuroimaging data stimulate the specification of hitherto only globally described components of functional psycholinguistic models.

How do bilinguals handle interhemispheric integration? Evidence from a cross-language study

The focus on interhemispheric interaction and integration has become a prominent aspect of laterality research. The aim of the present behavioral study was to determine whether hemisphere advantage differs between language groups. This was done by comparing how hemisphere advantage affects interhemispheric integration in monolingual and in bilingual individuals. Sixty university students (20 English monolinguals, 20 Hebrew bilinguals, and 20 balanced Arabic bilinguals) participated in two experiments, in which a lexical decision task was performed in the left and/or right visual field. Stimuli were presented unilaterally and bilaterally, whereby participants were cued to respond to the stimuli. In Experiment 1, all three groups showed an effect of lexicality, that is, participants responded to word stimuli faster than to non-word stimuli, with the Hebrew and Arabic groups showing a word advantage in spotting errors. In addition, all groups except the Hebrew group showed the expected right visual field advantage in accuracy, and the English group demonstrated this advantage in reaction time as well. In Experiment 2, responses to non-word stimuli were equally accurate in the left and right visual fields, but reaction time were faster for stimuli presented in the left visual field. The performance of balanced bilingual Arabic and unbalanced bilingual Hebrew reading groups was significantly better in the bilateral condition than in the unilateral condition. The results supported the notion that bilingual individuals show more effective interhemispheric communication and that they enjoy relative superiority in their interhemispheric processing in response to task demands.

Spatiotemporal dynamics of bilingual word processing

Studies with monolingual adults have identified successive stages occurring in different brain regions for processing single written words. We combined magnetoencephalography and magnetic resonance imaging to compare these stages between the first (L1) and second (L2) languages in bilingual adults. L1 words in a size judgment task evoked a typical left-lateralized sequence of activity first in ventral occipitotemporal cortex (VOT: previously associated with visual word-form encoding) and then ventral frontotemporal regions (associated with lexico-semantic processing). Compared to L1, words in L2 activated right VOT more strongly from approximately 135 ms; this activation was attenuated when words became highly familiar with repetition. At approximately 400 ms, L2 responses were generally later than L1, more bilateral, and included the same lateral occipitotemporal areas as were activated by pictures. We propose that acquiring a language involves the recruitment of right hemisphere and posterior visual areas that are not necessary once fluency is achieved.

Selective deficit of second language: a case study of a brain-damaged Arabic-Hebrew bilingual patient

BACKGROUND

An understanding of how two languages are represented in the human brain is best obtained from studies of bilingual patients who have sustained brain damage. The primary goal of the present study was to determine whether one or both languages of an Arabic-Hebrew bilingual individual are disrupted following brain damage. I present a case study of a bilingual patient, proficient in Arabic and Hebrew, who had sustained brain damage as a result of an intracranial hemorrhage related to herpes encephalitis.

METHODS

The patient's performance on several linguistic tasks carried out in the first language (Arabic) and in the second language (Hebrew) was assessed, and his performance in the two languages was compared.

RESULTS

The patient displayed somewhat different symptomatologies in the two languages. The results revealed dissociation between the two languages in terms of both the types and the magnitude of errors, pointing to aphasic symptoms in both languages, with Hebrew being the more impaired. Further analysis disclosed that this dissociation was apparently caused not by damage to his semantic system, but rather by damage at the lexical level.

CONCLUSION

The results suggest that the principles governing the organization of lexical representations in the brain are not similar for the two languages.

Performance in L1 and L2 observed in Arabic-Hebrew bilingual aphasic following brain tumor: A case constitutes double dissociation

This study aimed to verify the existence of a double first language (L1)/second language (L2) dissociation. In recent work, I described a case study of a Arabic-Hebrew aphasic patient (MH) with disturbances in the two languages, with Hebrew (L2) being more impaired. In this case, an Arabic-Hebrew bilingual patient (MM) with a similar cultural background who suffered brain damage following a left hemisphere tumor (oligodendroglioma) and craniotomy is reported. The same materials were used, which overcame methodological constraints in our previous work. The results revealed a complementary pattern of severe impairment of L1 (Arabic), while MM had mild language disorder in L2 (Hebrew) with intact semantic knowledge in both languages. These two cases demonstrate a double L1/L2 dissociation in unique languages, and support the notion that bilingual persons could have distinct cortical language areas.

Word order processing in the bilingual brain

One of the issues debated in the field of bilingualism is the question of a "critical period" for second language acquisition. Recent studies suggest an influence of age of onset of acquisition (AOA) particularly on syntactic processing; however, the processing of word order in a sentence context has not yet been examined specifically. We used functional MRI to examine word order processing in two groups of highly proficient German-French bilinguals who had either acquired French or German after the age of 10, and a third group which had acquired both languages before the age of three. Subjects listened to French and German sentences in which the order of subject and verb was systematically varied. In both groups of late bilinguals, processing of L2 compared to L1 resulted in higher levels of activation mainly of the left inferior frontal cortex while early bilinguals showed no activation difference in any of these areas. A selective increase in activation for late bilinguals only suggests that AOA contributes to modulating overall syntactic processing in L2. In addition, native speakers of French showed significantly higher activation for verb-subject-order than native German speakers. These data suggest that AOA effects may in particular affect those grammatical structures which are marked in the first language.

Bilingual aphasia due to spontaneous acute subdural haematoma from a ruptured intracranial infectious aneurysm

We report a case of spontaneous subdural haematoma due to ruptured intracranial infectious aneurysm, presenting with bilingual aphasia and illustrating differential language recovery. A 62-year-old right-handed bilingual gentleman, with a diagnosis of infective endocarditis, developed headache and became expressively aphasic in the English language. Three days later he was receptively and expressively aphasic in both English and Arabic. Cranial MRI scans showed a left-sided acute subdural haematoma with mass effect and midline shift. Contrast CT brain scans showed an enhancing speck adjacent to the clot and cerebral angiogram confirmed a distal middle cerebral artery aneurysm. He underwent image-guided craniotomy, evacuation of the subdural haematoma and excision of the aneurysm. Histopathological examination was consistent with an infectious intracranial aneurysm. Postoperatively his aphasia did not improve immediately. He had widened pulse pressure due to severe aortic regurgitation, confirmed on echocardiography. He underwent aortic valve replacement and mitral valve repair, following which his aphasia recovered gradually. Initially the recovery of his language was limited to Arabic. About a week later he recovered his English language as well. At 3-year follow-up he is doing well and has no neurological deficits. His aphasia has recovered completely. The present case is unique because of (a) presence of pure subdural haematoma, and (b) the differential susceptibility and recovery of native (L1) and acquired language (L2) in presence of a common pathology. The neurology of language in a bilingual is analysed and possible mechanisms discussed.

Neural aspects of second language representation and language control

A basic issue in the neurosciences of language is whether an L2 can be processed through the same neural mechanism underlying L1 acquisition and processing. In the present paper I review data from functional neuroimaging studies focusing on grammatical and lexico-semantic processing in bilinguals. The available evidence indicates that the L2 seems to be acquired through the same neural structures responsible for L1 acquisition. This fact is also observed for grammar acquisition in late L2 learners contrary to what one may expect from critical period accounts. However, neural differences for an L2 may be observed, in terms of more extended activity of the neural system mediating L1 processing. These differences may disappear once a more 'native-like' proficiency is established, reflecting a change in language processing mechanisms: from controlled processing for a weak L2 system (i.e., a less proficient L2) to more automatic processing. The neuroimaging data reviewed in this paper also support the notion that language control is a crucial aspect specific to the bilingual language system. The activity of brain areas related to cognitive control during the processing of a 'weak' L2 may reflect competition and conflict between languages which may be resolved with the intervention of these areas.

Identification of distinct and overlapping cortical areas for bilingual naming and reading using cortical stimulation. Case report

A bilingual pediatric patient who underwent tumor resection was mapped extraoperatively using cortical stimulation to preserve English and Hebrew languages. The authors mapped both languages by using 4 tasks: 1) English visual naming, 2) Hebrew visual naming, 3) read English/respond Hebrew, and 4) Hebrew reading. Essential cortical sites for primary and secondary languages were compared, photographically recorded, and plotted onto a schematic brain of the patient. Three types of sites were found in this patient: 1) multiuse sites (multiple tasks, both languages) in frontal, temporal, and parietal areas; 2) single-task sites (1 task, both languages) in postcentral and parietal areas; and 3) single-use sites (1 task, 1 language) in frontal, temporal, and parietal areas. These results lend support to the concept that bilingual patients can have distinct cortical representations of each language and of different language tasks, in addition to overlapping or shared sites that support both languages and multiple tasks.

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.

Brain potentials reveal unconscious translation during foreign-language comprehension

Whether the native language of bilingual individuals is active during second-language comprehension is the subject of lively debate. Studies of bilingualism have often used a mix of first- and second-language words, thereby creating an artificial "dual-language" context. Here, using event-related brain potentials, we demonstrate implicit access to the first language when bilinguals read words exclusively in their second language. Chinese-English bilinguals were required to decide whether English words presented in pairs were related in meaning or not; they were unaware of the fact that half of the words concealed a character repetition when translated into Chinese. Whereas the hidden factor failed to affect behavioral performance, it significantly modulated brain potentials in the expected direction, establishing that English words were automatically and unconsciously translated into Chinese. Critically, the same modulation was found in Chinese monolinguals reading the same words in Chinese, i.e., when Chinese character repetition was evident. Finally, we replicated this pattern of results in the auditory modality by using a listening comprehension task. These findings demonstrate that native-language activation is an unconscious correlate of second-language comprehension.

Age of acquisition modulates neural activity for both regular and irregular syntactic functions

Studies have found that neural activity is greater for irregular grammatical items than regular items. Findings with monolingual Spanish speakers have revealed a similar effect when making gender decisions for visually presented nouns. The current study extended previous studies by looking at the role of regularity in modulating differences in groups that differ in the age of acquisition of a language. Early and late learners of Spanish matched on measures of language proficiency were asked to make gender decisions to regular (-o for masculine and -a for feminine) and irregular items (which can end in e, l, n, r, s, t and z). Results revealed increased activity in left BA 44 for irregular compared to regular items in separate comparisons for both early and late learners. In addition, within-group comparisons revealed that neural activity for irregulars extended into left BA 47 for late learners and into left BA 6 for early learners. Direct comparisons between groups revealed increased activity in left BA 44/45 for irregular items indicating the need for more extensive syntactic processing in late learners. The results revealed that processing of irregular grammatical gender leads to increased activity in left BA 44 and adjacent areas in the left IFG regardless of when a language is learned. Furthermore, these findings suggest differential recruitment of brain areas associated with grammatical processing in late learners. The results are discussed with regard to a model which considers L2 learning as emerging from the competitive interplay between two languages.

Cortical activation during word processing in late bilinguals: Similarities and differences as revealed by functional magnetic resonance imaging

Functional magnetic resonance imaging was used to compare cortical organization of the first (L1, Russian) and second (L2, English) languages. Six fluent Russian-English bilinguals who acquired their second language postpuberty were tested with words and nonwords presented either auditorily or visually. Results showed that both languages activated similar cortical networks, including the inferior frontal, middle frontal, superior temporal, middle temporal, angular, and supramarginal gyri. Within the inferior frontal gyrus (IFG), L2 activated a larger cortical volume than L1 during lexical and phonological processing. For both languages, the left IFG was more active than the right IFG during lexical processing. Within the left IFG, the distance between centers of activation associated with lexical processing of translation equivalents across languages was larger than the distance between centers of activation associated with lexical processing of different words in the same language. Results of phonological processing analyses revealed different centers of activation associated with the first versus the second language in the IFG, but not in the superior temporal gyrus (STG). These findings are discussed within the context of the current literature on cortical organization in bilinguals and suggest variation in bilingual cortical activation associated with lexical, phonological, and orthographic processing.

Neural bases of asymmetric language switching in second-language learners: An ER-fMRI study

Using the ER-fMRI technique, the present study was designed to investigate the neural substrates of language switching among second-language learners. Twelve Chinese college students who were learning English were scanned when they performed language switching tasks (naming pictures in their first [L1, Chinese] and second [L2, English] languages according to response cues). Compared to non-switching conditions, language switching elicited greater activation in the right superior prefrontal cortex (BA9/10/32), left middle and superior frontal cortex (BA8/9/46), and right middle cingulum and caudate (BA11). When the direction of switching was considered, forward switching (from L1 to L2), but not backward switching (from L2 to L1), activated several brain regions related to executive functions (i.e., bilateral frontal cortices and left ACC) relative to non-switching conditions. These results suggest that neural correlates of language switching differ depending on the direction of the switch and that there does not seem to be a specific brain area acting as a "language switch".

Electrophysiological correlates of memory processing in early Finnish–Swedish bilinguals

Event-related desynchronization (ERD) and event-related synchronization (ERS) of the 1-30 EEG frequencies were studied in eight early Finnish-Swedish bilinguals during an auditory bilingual Sternberg memory task using Finnish-Swedish cognates as stimuli. Only subtle differences between languages were expected, since cognates have been assumed to have shared conceptual representations in the bilingual memory. Encoding elicited theta and alpha frequency ERS and beta frequency ERD responses in both languages. Retrieval elicited theta ERS and alpha and beta ERD responses. Some statistically significant differences between encoding and retrieval in Finnish versus Swedish emerged: greater theta and alpha ERS responses were observed during encoding in Swedish than during encoding in Finnish. During between-language retrieval, later-appearing theta ERS and alpha ERD responses were elicited as compared to within-language retrieval. These delayed oscillatory responses might reflect the involvement of central executive attentional functions in relation to language switching.

Effects of syntactic complexity in L1 and L2; An fMRI study of Korean–English bilinguals

The neural mechanisms underlying the syntactic processing of sentence comprehension in Korean (L1) and English (L2) by late bilinguals were investigated using functional MRI. The Korean native speakers were asked to read sentences with different levels of syntactic complexity in L1 and L2 and respond to comprehension questions concerning the sentences. The syntactic complexity was varied using a center-embedded sentence "The director that the maid introduced ignored the farmer" or a conjoined sentence "The maid introduced the director and ignored the farmer". It was found that the major areas involved in sentence processing such as the left inferior frontal gyrus (IFG), bilateral inferior parietal gyrus, and occipital lobe including cuneus, and lingual gyrus were commonly activated during the processing of both L1 and L2. However, the pattern of activation was different for L1 and L2 in the left IFG. The amount of activation was greater for embedded sentences than for conjoined sentences in L1 while no difference was found in L2. These results suggest that the cortical areas involved with syntactic processing in L1 and L2 are shared, but that the underlying neural mechanisms are different. The findings of the present study are discussed in comparison with Hasegawa et al.'s (Hasegawa, M., Carpenter, P.A., Just, M.A., 2002. An fMRI study of bilingual sentence comprehension and workload. NeuroImage 15, 647-660.) and Yokoyama et al.'s (Yokoyama, S., Okamoto, H., Miyamoto, T., Yoshimoto, K., Kim, J., Iwata, K., Jeong, H., Uchida, S., Ikuta, N., Sassa, Y., Nakamura, W., Horie, K., Sato, S., Kawashima, R., 2006. Cortical activation in the processing of passive sentences in L1 and L2: An fMRI study. NeuroImage 30, 570-579.) studies which also found common areas of activation but different patterns of activation during the processing of L1 and L2.

Neural basis of first and second language processing of sentence-level linguistic prosody

A fundamental question in multilingualism is whether the neural substrates are shared or segregated for the two or more languages spoken by polyglots. This study employs functional MRI to investigate the neural substrates underlying the perception of two sentence-level prosodic phenomena that occur in both Mandarin Chinese (L1) and English (L2): sentence focus (sentence-initial vs. -final position of contrastive stress) and sentence type (declarative vs. interrogative modality). Late-onset, medium proficiency Chinese-English bilinguals were asked to selectively attend to either sentence focus or sentence type in paired three-word sentences in both L1 and L2 and make speeded-response discrimination judgments. L1 and L2 elicited highly overlapping activations in frontal, temporal, and parietal lobes. Furthermore, region of interest analyses revealed that for both languages the sentence focus task elicited a leftward asymmetry in the supramarginal gyrus; both tasks elicited a rightward asymmetry in the mid-portion of the middle frontal gyrus. A direct comparison between L1 and L2 did not show any difference in brain activation in the sentence type task. In the sentence focus task, however, greater activation for L2 than L1 occurred in the bilateral anterior insula and superior frontal sulcus. The sentence focus task also elicited a leftward asymmetry in the posterior middle temporal gyrus for L1 only. Differential activation patterns are attributed primarily to disparities between L1 and L2 in the phonetic manifestation of sentence focus. Such phonetic divergences lead to increased computational demands for processing L2. These findings support the view that L1 and L2 are mediated by a unitary neural system despite late age of acquisition, although additional neural resources may be required in task-specific circumstances for unequal bilinguals.

Event-related EEG theta and alpha band oscillatory responses during language translation

Recent investigations on oscillatory EEG dynamics by means of event-related synchronisation and desynchronisation (ERS/ERD) suggest that first language semantic information processing is primarily reflected in the theta (4-7 Hz) and alpha (7-13 Hz) frequency bands. In this pilot study we explore whether similar ERS/ERD patterns emerge during language translation and which frequency bands sensitively respond to the difficulty of translation and the translation success. Thirteen female students of translation and interpreting were visually presented high and low frequency English words that had to be translated into German. Time-frequency representations of ERS/ERD between 2 and 50 Hz displayed a theta ERS response about 200-600 ms after word presentation, a beta ERD from about 400 ms, and alpha ERS and ERD patterns about 200-400 ms after word presentation. Statistical analyses of the ERS/ERD data in the theta (4-7 Hz), two alpha frequency bands (7-10 Hz and 10-13 Hz), and a beta band (20-30 Hz) predominantly revealed: (a) higher parietal theta ERS and frontal upper alpha ERD during the translation of low as compared to high frequency words, and (b) generally stronger ERD in the lower alpha band and larger left-hemispheric upper alpha ERD for successfully translated in contrast to not translated low frequency words. These findings provide first evidence of the sensitivity of the theta and alpha ERS/ERD measure to lexical-semantic processes involved in language translation.

Aphasic status epilepticus with periodic lateralized epileptiform discharges in a bilingual patient as a presenting sign of "AIDS-toxoplasmosis complex"

We describe an HIV-infected, bilingual patient presenting with Wernicke's aphasia due to partial status epilepticus with periodic lateralized epileptiform discharges, as the first sign of AIDS-toxoplasmosis complex. The localization of the native and secondary language centers in the brain and the possible role of recurrent seizures in the fluctuating course of Wernicke's aphasia in this patient are discussed. The clinical course of this patient supports the belief that a second language area for a second language learned in the later stages of life is located in an area different from that for the native language but still in close proximity to it.

Convergence, degeneracy and control

Understanding the neural representation and control of language in normal bilingual speakers provides insights into the factors that constrain the acquisition of another language, insights into the nature of language expertise and an understanding of the brain as an adaptive system. We illustrate both functional and structural brain changes associated with acquiring other languages and discuss the value of neuroimaging data in identifying individual differences and different phenotypes. Understanding normal variety is vital too if we are to understand the consequences of brain-damage in bilingual and polyglot speakers.

Intraoperative Language Localizationin Multilingual Patients With Gliomas

OBJECTIVE

Intraoperative localization of speech is problematic in patients that are fluent with different languages. Previous studies have generated various results depending on the series of patients studied, the type of language and the sensitivity of the tasks applied. It is not clear if languages are mediated by multiple and separate cortical areas, or shared by common areas. Globally considered, previous studies recommended performing a multiple intra-operative mapping for all the languages the patient is fluent for. Aim of this work was to study the feasibility of performing an intra-operative multiple language mapping in a group of multilingual patients with a glioma undergoing awake craniotomy for tumor removal, to describe the intraoperative cortical and subcortical findings in the area of craniotomy, with the final goal to maximally preserve their functional language.

METHODS

Seven late highly proficient multilingual patients with a left frontal glioma were submitted pre-operatively to a battery of tests to evaluate oral language production, comprehension, and repetition. Each language was tested serially starting from the first acquired language. Items which were correctly named during these tests were used to build personalized blocks to be used intraoperatively. Language mapping was undertaken during awake craniotomies, by the use of a Ojemann cortical stimulator during counting and oral naming tasks. Subcortical stimulation by using the same current threshold was applied during tumor resection, in a back and forth fashion, and the same tests.

RESULTS

Cortical sites essential for oral naming were found in 87.5% of patients, those for the first acquired language in 1 to 4 sites, those for the other languages in 1 to 3 sites. Sites for each language were distinct and separate. Number and location of sites were not predictable, being randomly and widely distributed in the cortex around or less frequently over the tumor area. Subcortical stimulations found tracts for the first acquired language in 4 patients, and for the other languages in 3 patients. Three of these patients decreased their fluency immediately after surgery, affecting the first acquired language, which fully recovered in two patients and partially in one. The procedure was agile and well tolerated by the patients.

CONCLUSION

These findings show that multiple cortical and subcortical language mapping during awake craniotomy for tumor removal is a feasible procedure. They support the concept that intraoperative mapping should be performed for all the languages the patient is fluent for to preserve functional integrity.

Cultural and linguistic influence on brain organization for language and possible consequences for dyslexia: a review

Current neuroimaging and neurophysiologic techniques have substantially increased our possibilities to study processes related to various language functions in the intact human brain. Learning to read and write influences the functional organization of the brain. What is universal and what is specific in the languages of the world are important issues. Most studies on healthy bilinguals indicate that essentially the same neural mechanisms are used for first and second languages, albeit with some linguistic and cultural influences related to speech and writing systems, particularly between alphabetical and nonalphabetical languages. Proficiency, age of acquisition, and amount of exposure can affect the cerebral representations of the languages. Accumulating data support the important role of working memory for acquiring high proficiency in the reading of native and second languages. It is proposed that longitudinal studies on second language acquisition are essential and that the specific problems related to second language learning in dyslexic children should have high priority.

The different frameworks underlying abstract and concrete knowledge: evidence from a bilingual patient with a semantic refractory access dysphasia

We report the case of a bilingual patient (IRQ) who acquired a semantic refractory access dysphasia following a middle cerebral artery stroke. In a series of spoken word-written word matching tasks, the degree of semantic similarity between target and distractor items was found to affect the accuracy of IRQ's identification of concrete but not abstract words. By contrast, the degree of semantic association between target and distractor items was found to affect response accuracy when identifying abstract but not concrete words. These results provide further corroboration for the notion that abstract concepts are supported by an associative representational network whereas concrete concepts are supported by a categorical representational framework. We also demonstrate an equivalent refractory deficit of comprehension in both English and Arabic. In addition, we provide the first documented evidence of a category-specific refractory deficit of knowledge for abstract words.

Bilingual brain organization: A functional magnetic resonance adaptation study

We used functional magnetic resonance adaptation (fMRA) to examine whether intra-voxel functional specificity may be present for first (L1)- and second (L2)-language processing. We examined within- and across-language adaptation for spoken words in English-French bilinguals who had acquired their L2 after the age of 4 years. Subjects listened to words presented binaurally through earphones. In two control conditions (one for each language), six identical words were presented to obtain maximal adaptation. The remaining six conditions each consisted of five words that were identical followed by a sixth word that differed. There were thus a total of eight experimental conditions: no-change (sixth word identical to first five); a change in meaning (different final word in L1); a change in language (final item translated into L2); a change in meaning and language (different final word in L2). The same four conditions were presented in L2. The study also included a silent baseline. At the neural level, within- and across-language word changes resulted in release from adaptation. This was true for separate analyses of L1 and L2. We saw no evidence for greater recovery from adaptation in across-language relative to within-language conditions. While many brain regions were common to L1 and L2, we did observe differences in adaptation for forward translation (L1 to L2) as compared to backward translation (L2 to L1). The results support the idea that, at the lexical level, the neural substrates for L1 and L2 in bilinguals are shared, but with some populations of neurons within these shared regions showing language-specific responses.

Native and non-native reading of sentences: An fMRI experiment

The processing of syntactic and semantic information in written sentences by native (L1) and non-native (L2) speakers was investigated in an fMRI experiment. This was done by means of a violation paradigm, in which participants read sentences containing either a syntactic, a semantic, or no violation. The results of this study were compared to those of a previous fMRI study, in which auditory sentence processing in L1 and L2 was investigated. The results indicate greater activation for L2 speakers as compared to L1 speakers when reading sentences in several language- and motor-related brain regions. The processing of syntactically incorrect sentences elicited no reliably greater activation in language areas in L2 speakers. In L1 speakers, on the other hand, syntactic processing, as compared to semantic processing, was associated with increased activation in left mid to posterior superior temporal gyrus. In response to the processing of semantically incorrect sentences, both L2 and L1 speakers demonstrated increased involvement of left inferior frontal gyrus. The results of this study were compared to a previously conducted fMRI study, which made use of identical sentence stimuli in the auditory modality. Results from the two studies are in general agreement with one another, although some differences in the response of brain areas very proximal to primary perceptual processing areas (i.e. primary auditory and visual cortex) were observed in conjunction with presentation in the different modalities. The combined results provide evidence that L1 and L2 speakers rely on the same cortical network to process language, although with a higher level of activation in some regions for L2 processing.

Hemispheric differences for identification of words and nonwords in urdu-English bilinguals

Hemispheric asymmetry was examined for Urdu-English bilinguals identifying printed Urdu words and nonwords, separated Urdu letter strings, digits, and English nonwords. In all cases, fewer errors occurred when stimuli were presented to the right visual field/left hemisphere (RVF/LH) than to the left visual field/right hemisphere (LVF/RH). Qualitative error patterns suggested that separated Urdu letter strings were processed more serially than Urdu letter strings joined to form words or pronounceable nonwords and more serially on RVF/LH than on LVF/RH trials. This qualitative laterality effect is similar to that found for Hebrew and Arabic but opposite that found for English and suggests that the qualitative manner of processing printed verbal material is influenced by language-specific factors such as scanning direction, orthographic-to-phonological mapping rules, and morphology.

Syntax production in bilinguals

We used fMRI to examine the functional correlates of syntactical processing in the first (L1) and second (L2) languages of non-proficient, late bilinguals. Subjects either covertly read words or produced sentences from them. Syntactical production during sentence production activated regions including left inferior frontal (LIFG) gyrus and the supplementary motor area in both languages. Analyses performed on the LIFG activation identified on a subject-by-subject basis revealed greater activation in L2 compared to L1 during sentence production and during word reading, consistent with previous work suggesting that greater cognitive effort may be subserved by less well-tuned neural representations that require greater neuronal activity. Remarkably, there was a greater separation in the LIFG activations in L1 versus L2 in less compared to more proficient bilinguals during syntax production, suggesting a functional reorganisation of regions involved in syntactical production as a function of syntactical proficiency.

Cortical activation in the processing of passive sentences in L1 and L2: an fMRI study

The question of whether the bilingual brain processes a first and second language (L1 and L2, respectively) differently is a central issue in many psycholinguistic and neurolinguistic studies. This study used functional magnetic resonance imaging (fMRI) to investigate whether late bilinguals process structurally complex sentences in L1 and L2 in different cortical networks. For this purpose, we directly compared brain activity during the processing of active and passive sentences in both L1 and L2. We asked 36 healthy subjects to judge whether or not a presented sentence was semantically plausible. Both L1 and L2 activated the left hemispheric language-related regions such as the left inferior frontal, superior/middle temporal, and parietal cortices. However, we found different activation patterns between L1 and L2 in the processing of passive sentences. Passive sentences elicited greater activation than their active counterparts in the left pars triangularis, the premotor area, and the superior parietal lobule in Japanese, but not in English. Furthermore, there was a significant interaction between sentence type (active versus passive) and language (Japanese versus English) in the left pars orbitalis. The results of this study indicate that late bilinguals use similar cortical regions to comprehend both L1 and L2. However, when late bilinguals are presented with structurally complex sentences, the involvement of these regions differs between L1 and L2. These results suggest that, in addition to age of L2 acquisition and L2 proficiency, differences in grammatical construction affect cortical representation during the comprehension of L1 and L2.

Phonological processing in Chinese-English bilingual biscriptals: an fMRI study

Different activation loci have been reported for language processing in unilingual Chinese and unilingual English participants, as well as in bilingual readers of English and French, two alphabetic languages. Nevertheless, the extant imaging work on Mandarin-English bilinguals favors common neural substrates for English and Chinese, languages with contrasting oral and written forms. We investigated the phonological processes in reading for English-Chinese biscriptals using a homophone matching task with parallel behavioral (n = 28) and fMRI (n = 6) experiments. Unlike previous reports, we observed distinct regions of activation for Mandarin in the left and right frontal lobes, the left temporal lobe, and the right occipital lobe, plus distinct regions of activation for English bilaterally in both the frontal and parietal lobes. The implications of these novel findings are discussed with reference to language representation in bilinguals.

Articulation in early and late bilinguals?? two languages: evidence from functional magnetic resonance imaging

The network of cortical and subcortical regions that contribute to articulation was examined in bilinguals using functional magnetic resonance imaging. Participants were all fluent in French and English: half were bilingual from birth and half were 'late bilinguals' who had learned French after the age of 12. Overt articulation resulted in the bilateral activation of the motor cortex, basal ganglia and cerebellum, and also the supplementary motor area, independent of the language spoken. Furthermore, the threshold and extent of the network involved in articulation was identical for the two bilingual groups with the exception of greater variation in the left putamen for the late bilinguals. These data challenge claims that age of acquisition results in fundamental differences in the neural substrates that subserve language in bilinguals.

Understanding bilingual memory: models and data

Bilingual memory research in the past decade and, particularly, in the past five years, has developed a range of sophisticated experimental, neuropsychological and computational techniques that have allowed researchers to begin to answer some of the major long-standing questions of the field. We explore bilingual memory along the lines of the conceptual division of language knowledge and organization, on the one hand, and the mechanisms that operate on that knowledge and organization, on the other. Various interactive-activation and connectionist models of bilingual memory that attempt to incorporate both organizational and operational considerations will serve to bridge these two divisions. Much progress has been made in recent years in bilingual memory research, which also serves to illuminate general (language-independent) memory processes.

Functional separation of languages in the bilingual brain: a comparison of electrical stimulation language mapping in 25 bilingual patients and 117 monolingual control patients

Object. The aim of this investigation was to address three questions in bilingualism research: 1) are multiple languages functionally separated within the bilingual brain; 2) are these languages similarly organized; and 3) does language organization in bilinguals mirror that in monolinguals?

Methods. During awake dominant-hemisphere craniotomy in each of 25 bilingual patients, the authors mapped both languages by using identical object-naming stimuli. Essential sites for primary (L1) and secondary (L2) languages were compared. Sites were photographically recorded and plotted onto an anatomically referenced grid system. Language organization in bilinguals was then compared with that in 117 monolinguals and 11 monolingual children.

Conclusions. The authors found distinct language-specific sites as well as shared sites that support both languages. The L1 and L2 representations were similar in total cortical extent but significantly different in anatomical distribution. The L2-specific sites were located exclusively in the posterior temporal and parietal regions, whereas the L1 and shared sites could be found throughout the mapped regions. Bilinguals possessed seven perisylvian language zones, in which L2 sites were significantly underrepresented when compared with the distribution of language sites in monolinguals. These L2-restricted zones overlapped the primary language areas found in monolingual children, indicating that these zones become dedicated to L1 processing. These findings support three conclusions. First, it is necessary to map both languages in bilinguals because L1 and L2 sites are functionally distinct. Second, differences exist in the organization of L1 and L2 sites, with L2-specific sites located exclusively in the posterior temporal and parietal lobes. Third, language organization comparisons in bilingual and monolingual brains demonstrate the presence of L2-restricted zones, which are dedicated to L1.

Phonetic perceptual identification by native- and second-language speakers differentially activates brain regions involved with acoustic phonetic processing and those involved with articulatory–auditory/orosensory internal models

This experiment investigates neural processes underlying perceptual identification of the same phonemes for native- and second-language speakers. A model is proposed implicating the use of articulatory-auditory and articulatory-orosensory mappings to facilitate perceptual identification under conditions in which the phonetic contrast is ambiguous, as in the case of second-language speakers. In contrast, native-language speakers are predicted to use auditory-based phonetic representations to a greater extent for perceptual identification than second-language speakers. The English /r-l/ phonetic contrast, although easy for native English speakers, is extremely difficult for native Japanese speakers who learned English as a second language after childhood. Twenty-two native English and twenty-two native Japanese speakers participated in this study. While undergoing event-related fMRI, subjects were aurally presented with syllables starting with a /r/, /l/, or a vowel and were required to rapidly identify the phoneme perceived by pushing one of three buttons with the left thumb. Consistent with the proposed model, the results show greater activity for second- over native-language speakers during perceptual identification of /r/ and /l/ relative to vowels in brain regions implicated with instantiating forward and inverse articulatory-auditory articulatory-orosensory models [Broca's area, anterior insula, anterior superior temporal sulcus/gyrus (STS/G), planum temporale (PT), superior temporal parietal area (Stp), SMG, and cerebellum]. The results further show that activity in brain regions implicated with instantiating these internal models is correlated with better /r/ and /l/ identification performance for second-language speakers. Greater activity found for native-language speakers especially in the anterior STG/S for /r/ and /l/ perceptual identification is consistent with the hypothesis that native-language speakers use auditory phonetic representations more extensively than second-language speakers.

Neural correlates of working memory for sign language

Eight, early bilingual, sign language interpreters participated in a PET study, which compared working memory for Swedish Sign Language (SSL) with working memory for audiovisual Swedish speech. The interaction between language modality and memory task was manipulated in a within-subjects design. Overall, the results show a previously undocumented, language modality-specific working memory neural architecture for SSL, which relies on a network of bilateral temporal, bilateral parietal and left premotor activation. In addition, differential activation in the right cerebellum was found for the two language modalities. Similarities across language modality are found in Broca's area for all tasks and in the anterior left inferior frontal lobe for semantic retrieval. The bilateral parietal activation pattern for sign language bears similarity to neural activity during, e.g., nonverbal visuospatial tasks, and it is argued that this may reflect generation of a virtual spatial array. Aspects of the data suggesting an age of acquisition effect are also considered. Furthermore, it is discussed why the pattern of parietal activation cannot be explained by factors relating to perception, production or recoding of signs, or to task difficulty. The results are generally compatible with Wilson's [Psychon. Bull. Rev. 8 (2001) 44] account of working memory.

Mapping of verbal working memory in nonfluent Chinese-English bilinguals with functional MRI

Existing cognitive and neural imaging studies have suggested a frontoparietal network of multiple, cooperative components for verbal working memory (WM). We used functional MRI to investigate whether this neural network is also involved in the processing of second language by nonfluent bilinguals. Twelve (five males, seven females) native Chinese speakers who had limited English proficiency were scanned while performing working memory tasks in Chinese and English. They were asked to make judgment continuously whether the word presented on the screen was semantically related to (i.e., the semantic tasks) another word presented two words earlier. On a different task (i.e., the phonological tasks), they were asked to make judgment whether the target word rhymed with the other word. A naming and judgment task in each language was adopted to control for the visual process, initial lexical process, and motor responses. Behavioral data showed that subjects performed better at tasks in their native language (Chinese, L1) than in English (L2). Imaging results showed that all working memory tasks in both L1 and L2 elicited a very similar pattern of left-hemisphere-dominated activation in the dorsolateral prefrontal cortex, pars opercularis region, pars triangularis region, precentral cortex, and parietal lobule. Consistent with the behavioral data, the volume of activation in the left opercularis region, left parietal lobule, and right precentral region was greater for L2 than for L1. These results suggest that working memory in L1 and L2 is mediated by a unitary neural system (i.e., frontoparietal region), which is capable of recruiting surrounding cortical resources to meet the increased computational demand caused by low L2 proficiency.

An fMRI study with semantic access in low proficiency second language learners

Brain activity was measured with fMRI in twelve 10- to 12-year-old Chinese children who began learning English when they were 8 years old in order to find out whether there is a common or a distinct neural semantic system for native language (L1) and second language (L2) in low proficiency bilingual subjects. Although they performed less well in L2 in the semantic decision task administered during fMRI measurement, these subjects showed similar robust activation, for both languages, in brain areas involved in semantic processing (e.g. the left inferior frontal cortex). Within-subject and group analyses revealed no significant difference in the activation patterns for L1 and L2 in these regions. These results suggest that at least at single-word level, there are shared neural substrates for semantic processing of L1 and L2 even when one is at a very low L2 proficiency level.

Bilingual corpus callosum variability

Magnetic resonance imaging was used to produce midsagittal images of the corpus callosum of 19 right-handed adult male and female subjects. The preliminary findings of this study indicate that significant adaptation in the anterior midbody of the corpus callosum has occurred to accommodate multiple language capacity in bilingual individuals compared to monolingual individuals. The main interpretation of this finding is that the precentral gyrus is involved in bilingual faculty adaptation assuming a role consistent with the somatotopical input to areas dedicated to the mouth, and input to association tracts connecting the premotor and supplementary motor cortices. This paper discusses possible implications to neuroscientists, second language educators, and their students.

Distributed neuronal networks for encoding category-specific semantic information: the mismatch negativity to action words

Mismatch negativity (MMN), an index of experience-dependent memory traces, was used to investigate the processing of action-related words in the human brain. Responses to auditorily presented movement-related English words were recorded in a non-attend odd-ball protocol using a high-density electroencephalographic (EEG) set-up. MMN was calculated using responses to the same words presented as standard and deviant stimuli in different sessions to avoid contamination from phonetic-acoustic differences. The topography of the mismatch negativity to action words revealed an unusual centro-posterior distribution of the responses, suggesting that activity was at least in part generated posterior to usually observed frontal MMNs. Moreover, responses to hand-related word stimulus (pick) had a more widespread lateral distribution, whereas leg-related stimulus (kick) elicited a more focal dorsal negativity. These differences, remarkably reminiscent of sensorimotor cortex topography, were further assessed using distributed source analysis of the EEG signal (L2 minimum-norm current estimates). The source analysis also confirmed differentially distributed activation for the two stimuli. We suggest that these results indicate activation of distributed neuronal assemblies that function as category-specific memory traces for words and may involve sensorimotor cortical structures for encoding action words.

Learning new sounds of speech: reallocation of neural substrates

Functional magnetic resonance imaging (fMRI) was used to investigate changes in brain activity related to phonetic learning. Ten monolingual English-speaking subjects were scanned while performing an identification task both before and after five sessions of training with a Hindi dental-retroflex nonnative contrast. Behaviorally, training resulted in an improvement in the ability to identify the nonnative contrast. Imaging results suggest that the successful learning of a nonnative phonetic contrast results in the recruitment of the same areas that are involved during the processing of native contrasts, including the left superior temporal gyrus, insula-frontal operculum, and inferior frontal gyrus. Additionally, results of correlational analyses between behavioral improvement and the blood-oxygenation-level-dependent (BOLD) signal obtained during the posttraining Hindi task suggest that the degree of success in learning is accompanied by more efficient neural processing in classical frontal speech regions, and by a reduction of deactivation relative to a noise baseline condition in left parietotemporal speech regions.

Language switching mechanisms in simultaneous interpreters: an ERP study

Recent event-related potential (ERP) and neuroimaging studies suggest that bilingual individuals are able to inhibit the processing of a non-target language while speaking or reading in another language. The neural mechanisms subserving code switching still remain matter of debate. The aim of the present study was to shed some light on the neurofunctional bases of such mechanisms. ERPs were recorded in native Italian simultaneous interpreters and monolingual controls during a semantic processing task in which the subjects had to evaluate the sensibleness of final words of incomplete sentences. All participants were strictly right-handed. Interpreters knew at least four languages (from four to eight) at a professional level, from among 11 European and Asian languages, and had an excellent command of English (L2). Four hundred short sentences were presented visually; half of them had an unexpected final word, producing a semantic incongruence. Sentences could be entirely in Italian or in English (unmixed); alternatively, the body of the sentence could be in English and the final word in Italian or vice versa (mixed). ERPs were time locked to the onset of the final word. Both reaction times (RTs) and electrophysiological data indicated a lesser degree of hemispheric lateralization for linguistic function during L2 rather than L1 processing in interpreters. The first effect of lexical switching and code switching was recorded in the time window between 140 and 200 ms at left anterior sites. At N400 level, ERPs were significantly larger to L2 than to L1 words only in the mixed and not in the unmixed condition. No effect of language was observed in the unmixed condition, thus suggesting that the difference in L1/L2 processing was not related to a difference in proficiency, but rather to a different functional organization of semantic integration systems due to the later age of acquisition of L2 compared to L1. Interpreters were faster at reading and comprehending sentences in English ending with an Italian word than vice versa (L2 --> L1 switch).

Neural mechanisms underlying semantic and orthographic processing in Chinese-English bilinguals

Brain activation underlying language processing in Chinese-English bilinguals was examined using fMRI in an orthographic search and a semantic classification task. In both tasks, brain areas activated by Chinese characters and English words were very similar to tasks examining Chinese reading using Chinese pinyin (an alphabetic Chinese script) and Chinese characters. However, the degree of later-alization was different, with English words (second language) causing much more right hemisphere activation than Chinese characters (native language). These differences support the hypothesis that second language usage causes more right hemisphere activation than native language usage.

Changes in brain activation patterns associated with learning of Korean words by Japanese: an fMRI study

We used functional magnetic resonance imaging (fMRI) to explore the change in brain activation associated with the learning of Korean words written in Han-gul characters (K-words) by young Japanese at two stages. Subjects were 12 right-handed native Japanese without previous knowledge of Korean words and characters. On the first day they were taught the pronunciation and meaning of 20 K-words. Then, after the first fMRI session (on day 2), they were given a set of 20 cards with the words and corresponding photographs. They also received a tape and were instructed to memorize the 20 K-words by studying them every day until the day of the second fMRI session (day 16). During the fMRI sessions, 20 Japanese words written in kana syllabograms (J-words) and the 20 previously presented K-words, as well as 20 new K-words (Kn-words) were presented visually for silent reading. The first J-word reading, relative to the first K-word reading, showed activation in the left angular gyrus. K-word reading relative to J-word reading during both sessions showed activation in occipital regions. Within these activated areas, session by condition interaction was found only in the left angular gyrus. The interaction between session and condition resulted from the fact that the differences in blood oxygenation-level-dependent signals between K-words and J-words and between Kn-words and J-words were significantly greater in the first session than in the second session. From the results, we concluded that patterns of brain activation changed as the memory of the 20 K-words became fixed through daily practice and that reading of both Korean words and Japanese syllabograms engaged the left angular gyrus.

fMRI Evidence for Cortical Modification during Learning of Mandarin Lexical Tone

Functional magnetic resonance imaging was employed before and after six native English speakers completed lexical tone training as part of a program to learn Mandarin as a second language. Language-related areas including Broca's area, Wernicke's area, auditory cortex, and supplementary motor regions were active in all subjects before and after training and did not vary in average location. Across all subjects, improvements in performance were associated with an increase in the spatial extent of activation in left superior temporal gyrus (Brodmann's area 22, putative Wernicke's area), the emergence of activity in adjacent Brodmann's area 42, and the emergence of activity in right inferior frontal gyrus (Brodmann's area 44), a homologue of putative Broca's area. These findings demonstrate a form of enrichment plasticity in which the early cortical effects of learning a tone-based second language involve both expansion of preexisting language-related areas and recruitment of additional cortical regions specialized for functions similar to the new language functions.

Functional MRI study of semantic and phonological language processing in bilingual subjects: preliminary findings

The objective of the study was to explore differences in regional fMRI activation topography and lateralization between semantic and phonological tasks performed in English and Spanish in bilingual individuals. Eight bilingual (primary Spanish and secondary English-speaking) individuals performed fMRI noun-verb association and rhyming tasks in both Spanish and English. Functional dataset analysis within Statistical Parametric Mapping (SPM99) with overlay on T1-weighted anatomic images was performed. Significantly higher laterality indices were noted in the semantic tasks as compared with the phonological tasks in the anterior regions of interest comprising the frontal and superior temporal lobes. A task subtraction analysis demonstrated right hemispheric (inferior frontal gyrus and supramarginal gyrus) foci of significantly increased activation in the combined language phonological tasks compared to the combined language semantic tasks; similarly prominent right hemispheric activation was seen in the English phonological-English semantic subtraction, but the analogous Spanish task subtraction revealed no task-related differences. This divergence in activation topography between semantic and phonological tasks performed in the nonnative language, but not in the primary language, suggests that neural networks utilized for phonological and semantic language processing in the nonnative language may not be as similar as those in the primary language.