Multilingual brain

The Multilingual Brain
This report discusses the neuroscientific and social aspect of the Multilingual
Brain. It discusses how language is stored in brain, how multilingual brain is
different from monolingual brain, how multilinguals use language, advantages and
disadvantages of being a multilingual etc. Since most of the research which is
done regarding multilingualism is done on bilingual individuals,
Multilingual/Bilingual have been used invariably throughout this report without
distinguishing between them and they both refer to same thing unless mentioned
otherwise
2013
Prakhar Asthana
Entry No:2011CS1027
3/29/2013

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1. Who is Bilingual?
According to current linguistic, psychological, and neurolinguistic approaches,
the term ‘‘bilingual’’ refers to all those people who use two or more languages
or dialects in their everyday lives (Grosjean 1994). In this report, dialects are
subsumed under the term ‘‘language.’’
2. Types of Bilinguals
Though bilingualism may be classified according to the pairing up of the
languages spoken, Weinreich (1963) discussed three types bilingualism in
terms of the ways in which it was thought that the concepts of a language
were encoded in the individual’s brain (Romaine, 1995). These are:
 Compound Bilinguals: Has one semantic system but two linguistic
codes. Usually refers to someone whose two languages are learnt at
same time, often in same context.
 Coordinate Bilinguals: Has two semantic systems and two linguistic
codes. Usually refers to someone whose two languages are learnt in two
languages are learnt in distinctively separate contexts.
 Subordinate bilingual: The weaker language is represented to the
stronger language.
Following figure illustrates mental lexicon of all types of bilinguals

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3. Hemispherical Lateralization of
Language
It refers to the distinction between
functions of the right and the left
hemispheres of the brain. Involvement of
one hemisphere of brain to a particular
activity makes it dominant[1]
. Language is
believed to be heavily lateralized function,
with left hemisphere dominating the right
one in handling language related tasks. It is
suggested that that language lateralization
depends on handedness, sex,
multilingualism, sign-language and also vary
among cultures.
It is been found out that it is left hemisphere that controls lexical and syntactic
language, writing and speech[2]
, phonetics and semantics. Split-brain studies
present evidence that, despite the right hemisphere having no “speech”, one is
still able to understand language through the auditory system. It does not
mean that right hemisphere serves no purpose. Patients which undergo
hemispherectomy to get their right hemisphere surgically removed show no
aphasia, but do show deficiencies in verbal selection and metaphor
understanding.

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4. How multilinguals switch between languages?
Researchers have used brain imaging techniques like functional magnetic
resonance imaging (fMRI) to investigate which brain regions are active when
bilingual people perform tasks in which they are forced to alternate between
their two languages. For instance, when bilingual people have to switch
between naming pictures in Spanish and naming them in English, they show
increased activation in the dorsolateral prefrontal cortex (DLPFC), a brain
region associated with cognitive skills like attention and inhibition[3]
Along with
the DLPFC, language switching has been found to involve such structures as the
anterior cingulate cortex (ACC), bilateral supermarginal gyri, and left inferior
frontal gyrus (left-IFG), regions that are also involved in cognitive control.[4]
The
left-IFG in particular, often considered the language production center of the
brain, appears to be involved in both linguistic and non-linguistic cognitive
control.
Other than this, Semantic priming techniques show that the left caudate is also
responsible for switching from one language to another. Patients with damage
or lesion in this part of brain undergo involuntary change in language while
speaking.[5]
5. How multilingual brain is different?
One of the most interesting questions in Neurolinguistics is the representation
of language in bilingual and the multilingual subjects. A fundamental issue is
whether the cerebral representation in the bi- and multilinguals differ from
that of monolinguals, and if so, in which specific way. This is an
interdisciplinary question which needs to identify and differentiate different
levels involved in the neural representation of languages, such as
neuroanatomical, neurofunctional, biochemical, psychological and linguistic
levels.
Do multilingual speakers use different areas of brain for different language? Or
same part of brain is used. A major hypothesis is that in individuals speaking

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two or more languages the different languages are represented and processed
in distinct brain regions. Studies conducted on bilingual aphasiac patients show
that in most of the cases only one of the mastered language is affected.[6]
This
gives an indirect proof to the above mentioned hypothesis.
I. Distinct/Shared areas associated with native and
second languages
The ability to acquire and use several languages selectively is a unique and
essential human capacity.
Eye tracking studies show that at early stages of language acquisition both
the languages are parallely activated and have shared cortical structures [7]
but fMRI scans show that for the late acquitted languages, language
sensitive regions in the frontal lobe of brain (Broca’s Area) are spatially
separated from that of language sensitive regions of native language. But
when second language is acquired early, native and second language
sensitive areas tend to overlap.
But in both late and early bilingual subjects, the temporal-lobe language-
sensitive regions (Wernicke's area) also show effectively little or no
separation of activity based on the age of language acquisition.[8]
However it does not mean that, first and second languages have all the
regions of brain in common. fMRI scans show that there are also language
specific zones in brain with L2-specific sites located exclusively in the
posterior temporal and parietal lobes. 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.[9]
II. Structural Plasticity of bilingual brain
It is found out that age of second language acquisition and proficiency in
that language affects the grey matter density of the brain[10]
learning a

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second language increases the density of grey matter in the left anterior
parietal cortex and it is modulated by the proficiency attained and the age
of acquisition

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III. More brain activation in bilingual brain
Putamen is a round structure
located at the base of the forebrain
According to the PET scan [11]
Left
putamen plays a significant role in
articulation of second language L2
(learned after the age of 5 years).
Cerebral Blood Flow (CBF) was
measured and only significant
change that was observed while
repeating words in first and second language (L1 and L2) was increased
CBF in the left putamen when words in L2 language were articulated.
Role of putamen in articulation is supported by the fact that Foreign
Accent Syndrome (FAS) in which patients develop what appears to be a
foreign accent can occur after left putaminal damage.
Word generation (phonemic verbal fluency) has also led to larger foci of
brain activation for the least fluent language(s) within multilinguals
(observed using fMRI). Regardless of language, however, activation is
principally found in the left prefrontal cortex (inferior frontal, middle
frontal, and precentral gyri). Additionally, activation can be observed in
the supplementary motor area and parietal lobe. [12]
6. Effect of Age of Acquisition
It is suggested that the first language might have more subcortical
representation than the second language and the subcortical organization of
languages in bilingual brain can change according to the age of acquisition of
second language.
It is also found that The age of second language acquisition determines the
variability in activation elicited by narration in three languages in Broca's and

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Wernicke's area.[13]
Studies done on trilinguals show that more neural
substrates are engaged in performing same language tasks for later acquired
languages[14]
. This activation is larger for L3 than L2 and L1, and less for L1 than
for L2. Familiarity with a language reduces the brain activation required for its
use
7. Effect of Proficiency in Language
Functional neuroimaging research has shown that very early bilinguals display
no difference in brain activation for L1 and L2 — which is assumed to be due to
high proficiency in both languages. Additionally, in highly proficient late
bilinguals, there is a common neural network that plays an important role in
language production tasks[15]
whereas, in less proficient late bilinguals,
spatially separated regions are activated in Broca's area for L1 and L2[8]
Finally,
it has been found that larger cerebral activation is measured when a language
is spoken less fluently than when languages are spoken more fluently [16]

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8. But which matters more- Proficiency or Age of
Acquisition?
Does individuals which have learned second language at a later stage of their
life but have mastered it upto the level of excellence tends to have same or
different cerebral representation as compared to individuals who learnt
second language early in their life? In other words is cerebral representation of
early bilinguals is same as late proficient bilinguals? Or more specifically if two
persons have same proficiency level in second language do they tend to have
same or different representation of languages in their brain even if their age of

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acquisition of second language is different? Does proficiency is more
preferable 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 than
age of acquisition in the cerebral representation of languages[17]
. Cerebral
representation is going to be same for two languages if one is equally
proficient in both of them. It doesn’t matter when they were acquired.
9. Bimodal Individuals
Bimodal individuals are those who are fluent in both sign language and oral
language. Neuroscientific research on Bimodal individuals has been carried
out. The effect of this experience on the brain compared to brain regions in
monolinguals or bilinguals has only recently become a research interest. It is
now used to provide insight on syntactic integration and language control of
bilinguals[18]
. PET scans from these studies show that there is separate region
in the brain for working memory related to sign language production and use.
These studies also find that Bimodal individuals use different areas of the right
hemisphere depending on whether if they are speaking using verbal language
or 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 right
hemisphere activity compared to normal controls during spontaneous
generation 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 both
cases[21]
fNIR scans comparing brain activity of bimodal bilinguals with those of oral
language and sign language monolinguals in picture naming tasks has been
done. These scans show that bimodal bilinguals show greater signal intensity

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in Wernicke’s area while using both languages in rapid alternation as
compared to the oral and sign language monolinguals [22]
.
10. Bilingual Aphasia
Bilingual aphasia is a specific form of aphasia which affects one or more
languages of a bilingual (or multilingual) individual. An abundance of insight
about language storage in the brain comes from studying bilingual/ mulilingual
individuals afflicted with a form of aphasia.
The symptoms and severity of aphasia in bilinguals/ mulitlinguals depend on
how many languages the individual knows, what order they have them stored
in the brain, how frequently they use each one, how proficient they are in
using those languages and patient's levels of education and literacy.[24]
I. Theories of assessing bilingual aphasia
There are two proposed theoretical views generally taken to approach
bilingual aphasia[37].
 Localizationist View
 Dynamic View
a) Localizationist View
It is the traditional view of assessing bilingual aphasia. This approach
views different languages as stored in different regions of the brain;
therefore, is the reason why bilingual/ multilingual aphasics may lose
one language they know, but not the other(s).[25]
b)Dynamic View
This approach proposes that the language system of representation and
control is compromised as a result of damage.[26]
The dynamical theory
approach suggests that the language system is supervised by a dynamic
equilibrium between the existing language capabilities and the constant
alteration and adaptation to the communicative requirements of the
environment.[31][32]
This theory is supported by the functional imaging
data of normal bilinguals and holds that fluency in a language is lost
because of an increase in the activation threshold. The Dynamic view

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offers an explanation for selective recovery of language and many
reported recovery patterns in bilingual aphasia [26]
II. Recovery from bilingual aphasia
The concept of different recovery patterns was first noted by Albert
Pitres in 1895. Since then, seven patterns have been outlined[26]
:
a) Differential recovery
It occurs when there is greater inhibition of one language than of
another. Recovery of L1 is more common than L2 in this recovery
mode [28]
.
b)Selective recovery
In this one language remains impaired and the other recovers; the
activation threshold for the impaired language is permanently
increased.
c) Parallel recovery
It occurs when both impaired languages improve to a similar extent
and concurrently.
d)Successive recovery
In this complete recovery of one language precedes the recovery of
the other.
e) Alternating recovery
In this the language that was first recovered will be lost again due to
the recovery of the language that was not first recovered.
f) Alternating antagonistic recovery
It occurs when the language that was not used for a time becomes
the currently used language i.e. on one day the patient is able to
speak in one language while the next day only in the other.

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g) Blended recovery
There is a pathological mixing of two languages i.e. the elements of
the two languages are involuntarily mixed during language
production.
Research that compares the prevalence of the different recovery patterns
generally shows that the most common pattern of recovery is parallel
recovery, followed by differential, blended, selective, and successive.[23]
In 1977, it was proposed that the recovery pattern of a bilingual aphasic
can be properly predicted if the effects of age, proficiency, context of
acquisition, and type of bilingualism are known in combined.[29]
It has
recently been reported that language status (how frequently the language
is used in comparison to other languages), lesion type or site, the context in
which the languages were used, the type of aphasia, and the manner in
which the language could not reliably predict recovery patterns.[30]
11. Advantages of bi/multi-lingualism
Studies show that the speed with which multilingual subjects perform
tasks, with-and-without mediation required to resolve language-use
conflict, is better in bilingual than monolingual subjects[40]
. Bilingual people
are also better than monolingual people at switching between two tasks;
for example, when bilinguals have to switch from categorizing objects by
color (red or green) to categorizing them by shape (circle or triangle), they
do so more rapidly than monolingual people, [33]
reflecting better cognitive
control when changing strategies on the fly.

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The cognitive and neurological benefits of bilingualism also extend into older
adulthood. Bilingualism appears to provide a means of fending off a natural
decline of cognitive function and maintaining what is called “cognitive
reserve.”[4]
Cognitive reserve refers to the efficient utilization of brain networks to
enhance brain function during aging. Bilingual experience may contribute to this
reserve by keeping the cognitive mechanisms sharp and helping to recruit
alternate brain networks to compensate for those that become damaged during
aging. Older bilingual people enjoy improved memory and executive
control relative to older monolingual people, which can lead to real-world health
benefits.
Bilingualism also helps during ageing. A recent study shows that being bilingual
can delay the onset of Alzheimer’s disease by about 4 years[34]
.

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In the subsequent study researches found out that bilingual test subjects’ brains
were more damaged as compared to monolingual test subjects’. But even then
they were able to resist Alzheimer’s disease for longer period. If the brain is an
engine, bilingualism may help to improve its mileage, allowing it to go farther on
the same amount of fuel.
12. Bilingualism – Always a boon?
Are there any disadvantages that are associated with being bilingual? Researches
show that bilinguals are slow at retrieving common words. They take longer time
and make more errors in naming tasks[39]
. This is so because their attention is
divided across multiple languages. It is found out that bilingual children have less
vocabulary in one language as compared to monolinguals [35]
.

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13. Questions still unanswered
Though a lot of study is being done in this area but still there are some
questions 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 more
advantage?
• Whether there is a limit to no. of languages upto which a person will always
be in gain?
• Whether there are any “better” languages that should be learnt?
Further studies are needed to elucidate the neuronal mechanisms of
bi/multilingual language processing. A promising perspective for future
bi/multilingual research is an integrative approach using brain imaging studies
with a high spatial resolution such as fMRI, combined with techniques with a
high temporal resolution, such as magnetoencephalography (MEG).

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36. http://www.brad.ac.uk/staff/pkkornakov/bilHermeneus2000.htm
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38. http://www.nytimes.com/2011/05/31/science/31conversation.html
39. http://www.researchgate.net/post/What_is_Multilingualism_How_is_it_useful_or_harmful_for_students
40. http://www.dana.org/news/cerebrum/detail.aspx?id=39638

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