Neuroscience of multilingualism is the study of multilingualism within the field of neurology. These studies include the representation of different language systems in the brain, the effects of multilingualism on the brain's structural plasticity, aphasia in multilingual individuals, and bimodal bilinguals (people who can speak at least one sign language and at least one oral language). Neurological studies of multilingualism are carried out with functional neuroimaging, electrophysiology, and through observation of people who have suffered brain damage.
The brain contains areas that are specialized to deal with language, located in the perisylvian cortex of the left hemisphere. These areas are crucial for performing language tasks, but they are not the only areas that are used; disparate parts of both the right and left brain hemispheres are active during language production. In multilingual individuals, there is a great deal of similarity in the brain areas used for each of their languages. Insights into the neurology of multilingualism have been gained by the study of multilingual individuals with aphasia, or the loss of one or more languages as a result of brain damage. Bilingual aphasics can show several different patterns of recovery; they may recover one language but not another, they may recover both languages simultaneously, or they may involuntarily mix different languages during language production during the recovery period. These patterns are explained by the dynamic view of bilingual aphasia, which holds that the language system of representation and control is compromised as a result of brain damage.
Research has also been carried out into the neurology of bimodal bilinguals, or people who can speak at least one oral language and at least one sign language. Studies with bimodal bilinguals have also provided insight into the tip of the tongue phenomenon, working memory, and patterns of neural activity when recognizing facial expressions, signing, and speaking.
Overview
Centralization of language areas in the brain
Language acquisition in multilingual individuals is contingent on two factors: age of the language acquisition and proficiency. Specialization is centered in the perisylvian cortex of the left hemisphere. Various regions of both the right and left hemisphere activate during language production. Multilingual individuals consistently demonstrate similar activation patterns in the brain when using either one of the two or more languages they fluently know. Age of acquiring the second-or-higher language, and proficiency of use determine what specific brain regions and pathways activate when using (thinking or speaking) the language. In contrast to those who acquired multiple languages at different points in their life, those who acquire multiple languages when young, and at virtually the same time, show similar activations in parts of Broca's area and left inferior frontal lobe. If the second-or-higher language is acquired later in life, specifically after the critical period, the language becomes centralized in a different part of Broca's area than the native language and other languages learned when young.
Brain plasticity in multilingualism
A greater density of grey matter in the inferior parietal cortex is present in multilingual individuals. It has been found that multilingualism affects the structure, and essentially, the cytoarchitecture of the brain. Learning multiple languages re-structures the brain and some researchers argue that it increases the brain's capacity for plasticity. Language learning boosts brain plasticity and the brain's ability to code new information. Early language learning plays a significant role in the formation of memory circuits for learning new information. Most of these differences in brain structures in multilinguals may be genetic at the core. Consensus is still muddled; it may be a mixture of both—experiential (acquiring languages during life) and genetic (predisposition to brain plasticity).
Experience can change both the function and the structure of the brain. Event-related brain potentials (ERPs) reflect synchronized postsynaptic activity in cortical pyramidal neurons. ERPs can be used to track learning-related changes in brain function. Semantic anomalies elicit a negative wave which suggests the separation between semantic and syntactic processing
Heightened brain plasticity in infants impacts later language development. Recent studies show that even brief exposure to a language in infancy changes how the brain processes a second-language acquisition. Participants in the studies who had transient language exposure as an infant or were multilingual showed greater brain activation in non-verbal working memory patterns, compared to monolingual speakers. The measure of uncommitted neural circuitry in infants can be accounted for in the perception of nonnative language at early stages of language acquisition. Research has shown that infants who show proficiency in nonnative phonetic perception at 7 months have slower language development than those who show proficiency in native phonetic perception. This research supports the Native Language Magnet/Neural Commitment Theory originally proposed by Patricia K. Kuhl.
Aphasia in multilingualism
Insights into language storage in the brain have come from studying multilingual individuals afflicted with a form of aphasia. The symptoms and severity of aphasia in multilingual individuals depend on the number of languages the individual knows, what order they learned them, and thus have them stored in the brain, the age at which they learned them, how frequently each language is used, and how proficient the individual is in using those languages. Two primary theoretical approaches to studying and viewing multilingual aphasics exist—the localizationalist approach and the dynamic approach. The localizationalist approach views different languages as stored in different regions of the brain, explaining why multilingual aphasics may lose one language they know, but not the other(s). The dynamical theory (or shared representation) 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. The dynamic approach views the representation and control aspects of the language system as compromised as a result of brain damage to the brain's language regions. The dynamic approach offers a satisfactory explanation for the various recovery times of each of the languages the aphasic has had impaired or lost because of the brain damage. Recovery of languages varies across aphasic patients. Some may recover all lost or impaired languages simultaneously. For some, one language is recovered before the others. In others, an involuntary mix of languages occurs in the recovery process; they intermix words from the various languages they know when speaking. Research affirms with the two approaches combined into the amalgamated hypothesis, it states that while languages do share some parts of the brain, they can also be allotted to some separate areas that are neutral.
Aphasia in multilinguals (or bilinguals) is commonly assessed through a Bilingual Aphasia Test (or BAT). The BAT consists of 3 sections that patients are required to answer with continuously as the test administrators record their answers. Patients' performances are then documented and processed with computer programs that determine the percentages of correctness given the specific linguistic skill. With the BAT many clinical settings have a standardized system of determining the extent of aphasia in the multilingual patients.
PET scan studies on bimodal individuals
Neuroscientific research on bimodal individuals—those who speak one oral language and one sign language—has been carried out. PET scans from these studies show that there is a 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 they are speaking using verbal language or gesticulating using sign language. Studies with bimodal bilinguals have also provided insight into the tip of the tongue phenomenon and into patterns of neural activity when recognizing facial expressions.
Role of the executive control system in preventing cross talk
There are sophisticated mechanisms to prevent cross talk in brains where more than one language is stored. The executive control system might be implicated to prevent one language from interfering with another in multilinguals. The executive control system is responsible for processes that are sometimes referred to as executive functions, and among others includes supervisory attentional system, or cognitive control. Although most research on the executive control system pertains to nonverbal tasks, there is some evidence that the system might be involved in resolving and ordering the conflict generated by the competing languages stored in the multilingual's brain. During speech production there is a constant need to channel attention to the appropriate word associated with the concept, congruent with the language being used. The word must be placed in the appropriate phonological and morphological context. Multilinguals constantly utilize the general executive control system to resolve interference/conflicts among the known languages, enhancing the system's functional performance, even on nonverbal tasks. In studies, multilingual subjects of all ages showed overall enhanced executive control abilities. This may indicate that the multilingual experience leads to a transfer of skill from the verbal to the nonverbal. Recent meta-analyses do not show any support for this assumed cognitive advantage. There is no one specific domain of language modulation in the general executive control system, as far as studies reveal. 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.
Health effects of multilingualism and bilingualism Despite the growth of multilingualism in different parts of the world, there are controversies on the positive and negative impacts of bilingualism on the education of children. Studies have brought part of the answer to frequent questions such as: are bilingual children distressed? Does multilingualism make children smarter? Defenders of multilingualism assert that speaking another language contributes to an intelligent and healthy brain whereas opponents of multilingualism vehemently insist that speaking another language does not make children smarter and that on the contrary, it can disturb their learning journey. Researcher Ellen Bialystok examined the effect of multilingualism on Alzheimer's disease and found that it delays its onset by about 4 years. The researcher's study found that those who spoke two or more languages showed symptoms of Alzheimer's disease at a later time than speakers of a single language. The study found that the more languages the multilingual knows, the later the onset of Alzheimer's disease. Lexical deficit results from second language acquisition. A research in 2025 found that multilingualism may delay aging.
Functional neuroimaging and language organization in the human brain