Multilingual brain


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Multilingual brain

  1. 1. The Multilingual BrainThis report discusses the neuroscientific and social aspect of the MultilingualBrain. It discusses how language is stored in brain, how multilingual brain isdifferent from monolingual brain, how multilinguals use language, advantages anddisadvantages of being a multilingual etc. Since most of the research which isdone regarding multilingualism is done on bilingual individuals,Multilingual/Bilingual have been used invariably throughout this report withoutdistinguishing between them and they both refer to same thing unless mentionedotherwise2013Prakhar AsthanaEntry No:2011CS10273/29/2013
  2. 2. The Multilingual Brain2 | P a g e1. Who is Bilingual?According to current linguistic, psychological, and neurolinguistic approaches,the term ‘‘bilingual’’ refers to all those people who use two or more languagesor dialects in their everyday lives (Grosjean 1994). In this report, dialects aresubsumed under the term ‘‘language.’’2. Types of BilingualsThough bilingualism may be classified according to the pairing up of thelanguages spoken, Weinreich (1963) discussed three types bilingualism interms of the ways in which it was thought that the concepts of a languagewere encoded in the individual’s brain (Romaine, 1995). These are: Compound Bilinguals: Has one semantic system but two linguisticcodes. Usually refers to someone whose two languages are learnt atsame time, often in same context. Coordinate Bilinguals: Has two semantic systems and two linguisticcodes. Usually refers to someone whose two languages are learnt in twolanguages are learnt in distinctively separate contexts. Subordinate bilingual: The weaker language is represented to thestronger language.Following figure illustrates mental lexicon of all types of bilinguals
  3. 3. The Multilingual Brain3 | P a g e3. Hemispherical Lateralization ofLanguageIt refers to the distinction betweenfunctions of the right and the lefthemispheres of the brain. Involvement ofone hemisphere of brain to a particularactivity makes it dominant[1]. Language isbelieved to be heavily lateralized function,with left hemisphere dominating the rightone in handling language related tasks. It issuggested that that language lateralizationdepends on handedness, sex,multilingualism, sign-language and also varyamong cultures.It is been found out that it is left hemisphere that controls lexical and syntacticlanguage, writing and speech[2], phonetics and semantics. Split-brain studiespresent evidence that, despite the right hemisphere having no “speech”, one isstill able to understand language through the auditory system. It does notmean that right hemisphere serves no purpose. Patients which undergohemispherectomy to get their right hemisphere surgically removed show noaphasia, but do show deficiencies in verbal selection and metaphorunderstanding.
  4. 4. The Multilingual Brain4 | P a g e4. How multilinguals switch between languages?Researchers have used brain imaging techniques like functional magneticresonance imaging (fMRI) to investigate which brain regions are active whenbilingual people perform tasks in which they are forced to alternate betweentheir two languages. For instance, when bilingual people have to switchbetween naming pictures in Spanish and naming them in English, they showincreased activation in the dorsolateral prefrontal cortex (DLPFC), a brainregion associated with cognitive skills like attention and inhibition[3]Along withthe DLPFC, language switching has been found to involve such structures as theanterior cingulate cortex (ACC), bilateral supermarginal gyri, and left inferiorfrontal gyrus (left-IFG), regions that are also involved in cognitive control.[4]Theleft-IFG in particular, often considered the language production center of thebrain, appears to be involved in both linguistic and non-linguistic cognitivecontrol.Other than this, Semantic priming techniques show that the left caudate is alsoresponsible for switching from one language to another. Patients with damageor lesion in this part of brain undergo involuntary change in language whilespeaking.[5]5. How multilingual brain is different?One of the most interesting questions in Neurolinguistics is the representationof language in bilingual and the multilingual subjects. A fundamental issue iswhether the cerebral representation in the bi- and multilinguals differ fromthat of monolinguals, and if so, in which specific way. This is aninterdisciplinary question which needs to identify and differentiate differentlevels involved in the neural representation of languages, such asneuroanatomical, neurofunctional, biochemical, psychological and linguisticlevels.Do multilingual speakers use different areas of brain for different language? Orsame part of brain is used. A major hypothesis is that in individuals speaking
  5. 5. The Multilingual Brain5 | P a g etwo or more languages the different languages are represented and processedin distinct brain regions. Studies conducted on bilingual aphasiac patients showthat in most of the cases only one of the mastered language is affected.[6]Thisgives an indirect proof to the above mentioned hypothesis.I. Distinct/Shared areas associated with native andsecond languagesThe ability to acquire and use several languages selectively is a unique andessential human capacity.Eye tracking studies show that at early stages of language acquisition boththe languages are parallely activated and have shared cortical structures [7]but fMRI scans show that for the late acquitted languages, languagesensitive regions in the frontal lobe of brain (Broca’s Area) are spatiallyseparated from that of language sensitive regions of native language. Butwhen second language is acquired early, native and second languagesensitive areas tend to overlap.But in both late and early bilingual subjects, the temporal-lobe language-sensitive regions (Wernickes area) also show effectively little or noseparation of activity based on the age of language acquisition.[8]However it does not mean that, first and second languages have all theregions of brain in common. fMRI scans show that there are also languagespecific zones in brain with L2-specific sites located exclusively in theposterior temporal and parietal lobes. Bilinguals possessed sevenperisylvian language zones, in which L2 sites were significantlyunderrepresented when compared with the distribution of language sites inmonolinguals. These L2-restricted zones overlapped the primary languageareas found in monolingual children, indicating that these zones becomededicated to L1 processing.[9]II. Structural Plasticity of bilingual brainIt is found out that age of second language acquisition and proficiency inthat language affects the grey matter density of the brain[10]learning a
  6. 6. The Multilingual Brain6 | P a g esecond language increases the density of grey matter in the left anteriorparietal cortex and it is modulated by the proficiency attained and the ageof acquisition
  7. 7. The Multilingual Brain7 | P a g eIII. More brain activation in bilingual brainPutamen is a round structurelocated at the base of the forebrainAccording to the PET scan [11]Leftputamen plays a significant role inarticulation of second language L2(learned after the age of 5 years).Cerebral Blood Flow (CBF) wasmeasured and only significantchange that was observed whilerepeating words in first and second language (L1 and L2) was increasedCBF in the left putamen when words in L2 language were articulated.Role of putamen in articulation is supported by the fact that ForeignAccent Syndrome (FAS) in which patients develop what appears to be aforeign accent can occur after left putaminal damage.Word generation (phonemic verbal fluency) has also led to larger foci ofbrain activation for the least fluent language(s) within multilinguals(observed using fMRI). Regardless of language, however, activation isprincipally found in the left prefrontal cortex (inferior frontal, middlefrontal, and precentral gyri). Additionally, activation can be observed inthe supplementary motor area and parietal lobe. [12]6. Effect of Age of AcquisitionIt is suggested that the first language might have more subcorticalrepresentation than the second language and the subcortical organization oflanguages in bilingual brain can change according to the age of acquisition ofsecond language.It is also found that The age of second language acquisition determines thevariability in activation elicited by narration in three languages in Brocas and
  8. 8. The Multilingual Brain8 | P a g eWernickes area.[13]Studies done on trilinguals show that more neuralsubstrates are engaged in performing same language tasks for later acquiredlanguages[14]. This activation is larger for L3 than L2 and L1, and less for L1 thanfor L2. Familiarity with a language reduces the brain activation required for itsuse7. Effect of Proficiency in LanguageFunctional neuroimaging research has shown that very early bilinguals displayno difference in brain activation for L1 and L2 — which is assumed to be due tohigh proficiency in both languages. Additionally, in highly proficient latebilinguals, there is a common neural network that plays an important role inlanguage production tasks[15]whereas, in less proficient late bilinguals,spatially separated regions are activated in Brocas area for L1 and L2[8]Finally,it has been found that larger cerebral activation is measured when a languageis spoken less fluently than when languages are spoken more fluently [16]
  9. 9. The Multilingual Brain9 | P a g e8. But which matters more- Proficiency or Age ofAcquisition?Does individuals which have learned second language at a later stage of theirlife but have mastered it upto the level of excellence tends to have same ordifferent cerebral representation as compared to individuals who learntsecond language early in their life? In other words is cerebral representation ofearly bilinguals is same as late proficient bilinguals? Or more specifically if twopersons have same proficiency level in second language do they tend to havesame or different representation of languages in their brain even if their age of
  10. 10. The Multilingual Brain10 | P a g eacquisition of second language is different? Does proficiency is morepreferable criteria than age of acquisition as compared to age of acquisition?Researches show that proficiency outweighs age of acquisition. In bilinguals,achieved proficiency, and possibly language exposure, are more crucial thanage of acquisition in the cerebral representation of languages[17]. Cerebralrepresentation is going to be same for two languages if one is equallyproficient in both of them. It doesn’t matter when they were acquired.9. Bimodal IndividualsBimodal individuals are those who are fluent in both sign language and orallanguage. Neuroscientific research on Bimodal individuals has been carriedout. The effect of this experience on the brain compared to brain regions inmonolinguals or bilinguals has only recently become a research interest. It isnow used to provide insight on syntactic integration and language control ofbilinguals[18]. PET scans from these studies show that there is separate regionin the brain for working memory related to sign language production and use.These studies also find that Bimodal individuals use different areas of the righthemisphere depending on whether if they are speaking using verbal languageor gesticulating using sign-language[19].PET scans of a sign language bilingual (English and American Sign Language)male with left frontal lobe damage revealed that there is an increased righthemisphere activity compared to normal controls during spontaneousgeneration of narrative in both English and American Sign Language (ASL).[20]fMRI scans show that showing sign language to deaf and hearing-abled signers(one who know sign language) and showing written English to hearing non-signers activates the classical language areas of the left hemisphere in bothcases[21]fNIR scans comparing brain activity of bimodal bilinguals with those of orallanguage and sign language monolinguals in picture naming tasks has beendone. These scans show that bimodal bilinguals show greater signal intensity
  11. 11. The Multilingual Brain11 | P a g ein Wernicke’s area while using both languages in rapid alternation ascompared to the oral and sign language monolinguals [22].10. Bilingual AphasiaBilingual aphasia is a specific form of aphasia which affects one or morelanguages of a bilingual (or multilingual) individual. An abundance of insightabout language storage in the brain comes from studying bilingual/ mulilingualindividuals afflicted with a form of aphasia.The symptoms and severity of aphasia in bilinguals/ mulitlinguals depend onhow many languages the individual knows, what order they have them storedin the brain, how frequently they use each one, how proficient they are inusing those languages and patients levels of education and literacy.[24]I. Theories of assessing bilingual aphasiaThere are two proposed theoretical views generally taken to approachbilingual aphasia[37]. Localizationist View Dynamic Viewa) Localizationist ViewIt is the traditional view of assessing bilingual aphasia. This approachviews different languages as stored in different regions of the brain;therefore, is the reason why bilingual/ multilingual aphasics may loseone language they know, but not the other(s).[25]b)Dynamic ViewThis approach proposes that the language system of representation andcontrol is compromised as a result of damage.[26]The dynamical theoryapproach suggests that the language system is supervised by a dynamicequilibrium between the existing language capabilities and the constantalteration and adaptation to the communicative requirements of theenvironment.[31][32]This theory is supported by the functional imagingdata of normal bilinguals and holds that fluency in a language is lostbecause of an increase in the activation threshold. The Dynamic view
  12. 12. The Multilingual Brain12 | P a g eoffers an explanation for selective recovery of language and manyreported recovery patterns in bilingual aphasia [26]II. Recovery from bilingual aphasiaThe concept of different recovery patterns was first noted by AlbertPitres in 1895. Since then, seven patterns have been outlined[26]:a) Differential recoveryIt occurs when there is greater inhibition of one language than ofanother. Recovery of L1 is more common than L2 in this recoverymode [28].b)Selective recoveryIn this one language remains impaired and the other recovers; theactivation threshold for the impaired language is permanentlyincreased.c) Parallel recoveryIt occurs when both impaired languages improve to a similar extentand concurrently.d)Successive recoveryIn this complete recovery of one language precedes the recovery ofthe other.e) Alternating recoveryIn this the language that was first recovered will be lost again due tothe recovery of the language that was not first recovered.f) Alternating antagonistic recoveryIt occurs when the language that was not used for a time becomesthe currently used language i.e. on one day the patient is able tospeak in one language while the next day only in the other.
  13. 13. The Multilingual Brain13 | P a g eg) Blended recoveryThere is a pathological mixing of two languages i.e. the elements ofthe two languages are involuntarily mixed during languageproduction.Research that compares the prevalence of the different recovery patternsgenerally shows that the most common pattern of recovery is parallelrecovery, followed by differential, blended, selective, and successive.[23]In 1977, it was proposed that the recovery pattern of a bilingual aphasiccan be properly predicted if the effects of age, proficiency, context ofacquisition, and type of bilingualism are known in combined.[29]It hasrecently been reported that language status (how frequently the languageis used in comparison to other languages), lesion type or site, the context inwhich the languages were used, the type of aphasia, and the manner inwhich the language could not reliably predict recovery patterns.[30]11. Advantages of bi/multi-lingualismStudies show that the speed with which multilingual subjects performtasks, with-and-without mediation required to resolve language-useconflict, is better in bilingual than monolingual subjects[40]. Bilingual peopleare also better than monolingual people at switching between two tasks;for example, when bilinguals have to switch from categorizing objects bycolor (red or green) to categorizing them by shape (circle or triangle), theydo so more rapidly than monolingual people, [33]reflecting better cognitivecontrol when changing strategies on the fly.
  14. 14. The Multilingual Brain14 | P a g eThe cognitive and neurological benefits of bilingualism also extend into olderadulthood. Bilingualism appears to provide a means of fending off a naturaldecline of cognitive function and maintaining what is called “cognitivereserve.”[4]Cognitive reserve refers to the efficient utilization of brain networks toenhance brain function during aging. Bilingual experience may contribute to thisreserve by keeping the cognitive mechanisms sharp and helping to recruitalternate brain networks to compensate for those that become damaged duringaging. Older bilingual people enjoy improved memory and executivecontrol relative to older monolingual people, which can lead to real-world healthbenefits.Bilingualism also helps during ageing. A recent study shows that being bilingualcan delay the onset of Alzheimer’s disease by about 4 years[34].
  15. 15. The Multilingual Brain15 | P a g eIn the subsequent study researches found out that bilingual test subjects’ brainswere more damaged as compared to monolingual test subjects’. But even thenthey were able to resist Alzheimer’s disease for longer period. If the brain is anengine, bilingualism may help to improve its mileage, allowing it to go farther onthe same amount of fuel.12. Bilingualism – Always a boon?Are there any disadvantages that are associated with being bilingual? Researchesshow that bilinguals are slow at retrieving common words. They take longer timeand make more errors in naming tasks[39]. This is so because their attention isdivided across multiple languages. It is found out that bilingual children have lessvocabulary in one language as compared to monolinguals [35].
  16. 16. The Multilingual Brain16 | P a g e13. Questions still unansweredThough a lot of study is being done in this area but still there are somequestions whose answers are yet to be found like• What is the best age at which one should start learning second language?• Whether the two languages should be similar or different to get moreadvantage?• Whether there is a limit to no. of languages upto which a person will alwaysbe in gain?• Whether there are any “better” languages that should be learnt?Further studies are needed to elucidate the neuronal mechanisms ofbi/multilingual language processing. A promising perspective for futurebi/multilingual research is an integrative approach using brain imaging studieswith a high spatial resolution such as fMRI, combined with techniques with ahigh temporal resolution, such as magnetoencephalography (MEG).
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