1. Introduction
Multilingualism has become increasingly prevalent in our globalized world. Compared to monolinguals, multilingual individuals must manage multiple languages in their daily communications, a capability underpinned by complex cognitive and neural mechanisms [1-5]. This linguistic versatility necessitates a sophisticated level of cognitive control, allowing multilinguals to switch between languages seamlessly and inhibit interference from non-target languages [6-9].
In recent years, researchers have employed various neuroimaging techniques, such as functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI), to explore the effects of multilingualism on brain structure and function [10-12]. These studies have revealed how multilinguals manage multiple languages and prevent interference between them, offering crucial insights into the cognitive control mechanisms and their neural bases. The use of these advanced imaging technologies has significantly deepened our understanding of the brain's adaptability and the neural networks involved in multilingual processing.
The purpose of this review is to summarize and analyze the latest research findings on multilingual brain processing, examining the unique aspects of cognitive control and language switching in multilingual individuals. By consolidating current knowledge and highlighting emerging trends, this paper aims to provide a comprehensive overview of the cognitive and neural underpinnings of multilingualism.
2. Structural Changes in the Multilingual Brain
2.1. Gray Matter Changes
Multilingualism significantly affects gray matter in the brain. Studies have found that individuals who speak multiple languages tend to have increased gray matter density in regions associated with language processing, such as the left inferior parietal cortex. This enhancement in gray matter is believed to contribute to improved cognitive functions, including better memory, problem-solving skills, and multitasking abilities. The continuous switching between languages and the need to manage multiple linguistic systems likely stimulate and strengthen these brain areas. Consequently, multilingualism not only facilitates communication across different languages but also supports overall cognitive health and resilience against age-related cognitive decline.
Pliatsikas et al. [13] found that multilingual individuals exhibit increased gray matter surface in regions such as the bilateral putamen, globus pallidus, and the right thalamus, which are crucial for language planning and execution. These regions are vital for language control and execution, while the thalamus is essential for the transmission and integration of language information. These findings suggest that multilingualism not only enhances neural connections in these areas but also improves their functional efficiency. Burgaleta et al. [14] and Ressel et al. [15] also found volume changes in various cortical and subcortical regions, such as the striatum, thalamus, and caudate nucleus, in multilingual individuals. These regions are involved in language processing and executive functions, further supporting the positive impact of multilingualism on gray matter. Specifically, the volume increases in the striatum and caudate nucleus may be related to multilinguals' advantages in language selection and control.
2.2. White Matter Changes
Multilingualism also induces significant structural changes in white matter. Multilingual individuals tend to exhibit higher fiber cross-sectional area and lower fiber density in key white matter pathways, such as the superior longitudinal fasciculus and the arcuate fasciculus. These pathways are essential for the transmission and integration of language information. The observed changes suggest that multilingualism enhances the structural integrity of these pathways, thereby improving the brain's efficiency in switching between languages and managing language interference. This structural adaptation highlights the profound impact that learning and using multiple languages can have on the brain's connectivity and overall cognitive function.
Pliatsikas [16] found that multilingual individuals exhibit higher fiber cross-sectional area and lower fiber density in white matter pathways such as the superior longitudinal fasciculus and the arcuate fasciculus. These pathways are crucial for the transmission and integration of language information. These changes suggest that multilingualism enhances the structural integrity of these pathways, improving the brain's efficiency in switching between languages and managing language interference.
Grogan et al. [17] further supported this view by demonstrating that structural changes in these pathways are closely related to language processing abilities in multilinguals. Specifically, their study found that multilinguals exhibited higher neural connectivity efficiency during language-switching tasks, suggesting that multilingualism enhances the overall efficiency of language processing through these white matter pathways.
Kaiser et al. [18] also reported similar findings. By comparing the white matter structure of multilinguals and monolinguals, they found significant structural changes in the superior longitudinal fasciculus, the arcuate fasciculus, and other white matter pathways in multilingual individuals. These pathways are essential for the transmission and integration of language information, and their structural enhancement may result from the increased frequency and complexity of language use.
3. Neural Networks Involved in Multilingual Processing
3.1. Complexity of Neural Networks
Multilingual processing involves complex neural networks that extend beyond traditional language areas (such as Broca’s and Wernicke’s areas) to include regions related to executive function and cognitive control [19,20]. Bialystok et al. [21,22] demonstrated that multilingual individuals exhibit higher cognitive control during task execution, which is associated with increased activity in brain regions involved in language control and executive control. Specifically, multilinguals show significant activation in the prefrontal cortex and parietal cortex during task execution, areas responsible for task switching and conflict resolution. The prefrontal cortex plays a crucial role in selecting the appropriate language and inhibiting interference from other languages, while the parietal cortex is involved in the allocation and management of attention.
The significance of these findings lies in the revelation that multilingualism involves not just language processing areas but also broader cognitive control networks. This suggests that multilinguals frequently engage in language switching and managing language interference, thereby enhancing the functions of these cognitive control regions. However, many studies have focused on task execution in laboratory settings, which may not fully reflect the real-life language processing of multilinguals.
3.2. Efficiency and Flexibility of Neural Networks
Multilinguals demonstrate higher efficiency and flexibility in their neural networks when switching languages and managing language interference. Grogan et al. [17] found that multilingual individuals exhibit higher neural connectivity efficiency in language-switching tasks, particularly in areas responsible for language processing and executive control. This increased efficiency indicates that multilinguals can switch between languages more quickly and accurately, reducing language interference and enhancing overall language processing capabilities.
However, these studies primarily rely on techniques such as fMRI and DTI, which, despite providing detailed structural and functional information about the brain, have limitations. For example, fMRI has low temporal resolution, making it difficult to capture rapid neural activity changes, while DTI mainly measures the structure of white matter pathways and does not directly reflect neuronal activity. Future research should combine multiple imaging techniques, such as magnetic resonance spectroscopy (MRS) and electrophysiological recording, to gain a more comprehensive understanding of the neural networks of multilinguals.
3.3. Dynamic Characteristics of Neural Networks
Pliatsikas [16] further pointed out that multilinguals exhibit faster reaction times and fewer errors in language-switching tasks, which are associated with increased activity in the prefrontal and parietal cortices. These dynamic characteristics indicate that the brains of multilingual individuals can more effectively adjust and adapt when processing language tasks, thereby improving the efficiency and accuracy of language processing.
The significance of these findings is that they provide evidence for how multilingualism enhances the brain’s dynamic adjustment capabilities to improve language processing efficiency. This not only helps in understanding the impact of multilingualism on brain function but also provides a theoretical basis for multilingual education and training. However, most current studies are cross-sectional and lack long-term tracking of neural network changes in multilinguals. Future research should adopt longitudinal designs to track brain changes in multilingual individuals across different age groups to reveal the long-term effects of multilingualism on neural networks.
4. Cognitive Advantages in Multilinguals
4.1. Enhancement of Executive Control
Multilingual individuals exhibit significant cognitive advantages in executive control tasks. Barac et al. [23] found that multilingual children outperform monolingual children in both behavioral and electrophysiological measures of executive control tasks. These tasks include conflict resolution and task switching, indicating that multilingualism can enhance executive functions such as task switching, conflict resolution, and working memory. These findings reveal how multilingualism enhances executive control capabilities, improving performance in complex tasks.
Bialystok et al. [24] also support this view, showing that multilingual individuals demonstrate higher prefrontal cortex activity during executive tasks, closely related to their enhanced cognitive control abilities. This suggests that multilingualism can improve executive functions by increasing prefrontal cortex activity, which is crucial for multitasking and conflict resolution. However, most of these studies rely on static imaging techniques, lacking real-time observation of dynamic brain changes during task execution. Future research should combine multiple imaging techniques, such as functional near-infrared spectroscopy (fNIRS) and electroencephalography (EEG), to more comprehensively reveal the impact of multilingualism on executive control.
4.2. Delay of Cognitive Decline
Multilingualism can also delay cognitive and neural decline. Bialystok et al. [25] found that bilingual individuals exhibit better cognitive functions in old age, particularly in executive control and memory tasks. The significance of this finding is that multilingualism can promote adaptive changes in brain structure and function by increasing neural plasticity, thereby slowing the process of cognitive decline. These findings suggest that multilingualism can be seen as an effective intervention to prevent and delay cognitive decline.
However, many of these studies are limited to short-term follow-ups and lack long-term tracking of the cognitive decline process. Future research should adopt longitudinal designs to observe changes in cognitive functions and brain structure in older adults, providing more comprehensive evidence for the impact of multilingualism on delaying cognitive decline.
5. Limitations and Future Directions
Despite significant advancements in understanding the impact of multilingualism on brain structure and function, several limitations remain. Most current studies have focused on adult multilinguals, with less attention given to children and older adults. Additionally, methodological differences, such as variations in neuroimaging techniques and data analysis methods, may affect the comparability of results.
Future research should address these limitations by examining the effects of multilingualism across different age groups and using standardized methodologies. Longitudinal studies are also needed to track the dynamic changes in brain structure and function over time. Combining multiple imaging techniques, such as fNIRS and EEG, can provide a more comprehensive understanding of the neural networks involved in multilingual processing.
6. Conclusion
The reviewed literature highlights the profound impact of multilingualism on brain structure and function, demonstrating significant enhancements in gray and white matter, and increased efficiency and flexibility in neural networks. These findings underscore the cognitive advantages multilinguals possess, particularly in executive control and delay of cognitive decline. However, existing research is limited by its focus on adults and methodological inconsistencies. Future research should expand to diverse age groups and adopt standardized, longitudinal approaches to track brain changes over time. By integrating multiple neuroimaging techniques, future studies can provide a more holistic understanding of how multilingualism shapes the brain and informs multilingual education and training strategies.
References
[1]. Luk, G., De Sa, E., & Bialystok, E. (2011). Is there a relation between onset age of bilingualism and enhancement of cognitive control?. Bilingualism: Language and Cognition, 14(4), 588-595.
[2]. Mechelli, A., Crinion, J. T., Noppeney, U., O'Doherty, J., Ashburner, J., Frackowiak, R. S. J., & Price, C. J. (2004). Structural plasticity in the bilingual brain. Nature, 431(7010), 757-761.
[3]. Moreno, E., Marques, C., Santos, A., et al. (2015). Language control in bilinguals. Brain and Cognition, 94, 15-21.
[4]. Hernandez, A. E., Martinez, A., & Kohnert, K. (2000). In search of the language switch: An fMRI study of picture naming in Spanish-English bilinguals. Brain and Language, 73(3), 421-431.
[5]. Sebastián-Gallés, N., & Bosch, L. (2002). Building phonotactic knowledge in bilinguals. Language and Speech, 45(4), 289-316.
[6]. Perani, D., & Abutalebi, J. (2005). The neural basis of first and second language processing. Current Opinion in Neurobiology, 15(2), 202-206.
[7]. Li, P., Legault, J., & Litcofsky, K. A. (2014). Neuroplasticity as a function of second language learning: Anatomical changes in the human brain. Cortex, 58, 301-324.
[8]. Olsen, R. K., Pangelinan, M. M., Bogulski, C., et al. (2015). The effect of lifelong bilingualism on regional grey and white matter volume. Brain Research, 1612, 1-12.
[9]. Park, D. C., & Reuter-Lorenz, P. (2009). The adaptive brain: Aging and neurocognitive scaffolding. Annual Review of Psychology, 60, 173-196.
[10]. Berken, J. A., Gracco, V. L., Chen, J. K., & Klein, D. (2016). The timing of language learning shapes brain structure associated with articulation. Brain Structure and Function, 221(1), 359-370.
[11]. Reiterer, S., Pereda, E., & Bhattacharya, J. (2009). Measuring second language proficiency with EEG synchronization: How functional cortical networks and hemispheric involvement differ as a function of proficiency level in second language speakers. Second Language Research, 25(1), 77-106.
[12]. Ibrahim, R., Israeli, N., & Eviatar, Z. (2010). Hemispheric involvement in reading: The effects of language experience. Journal of Neurolinguistics, 23(2), 130-145.
[13]. Pliatsikas, C., Moschopoulou, E., & Saddy, J. D. (2017). The effects of bilingualism on the white matter structure of the brain. Proceedings of the National Academy of Sciences, 114(7), 1-5.
[14]. Burgaleta, M., Sanjuán, A., Ventura-Campos, N., Sebastián-Gallés, N., & Ávila, C. (2016). Bilingualism at the core of the brain. Structural differences between bilinguals and monolinguals in the basal ganglia. Brain Structure and Function, 221(5), 1-12.
[15]. Ressel, V., Pallier, C., Ventura-Campos, N., Díaz, B., Roessler, A., Ávila, C., & Sebastián-Gallés, N. (2012). An effect of bilingualism on the auditory cortex. Journal of Neuroscience, 32(47), 16597-16601.
[16]. Pliatsikas, C. (2020). Understanding structural plasticity in the bilingual brain: The contribution of diffusion MRI. Bilingualism: Language and Cognition, 23(2), 1-11.
[17]. Grogan, A., Parker Jones, O., Ali, N., Crinion, J., Orabona, S., Mechias, M. L., & Price, C. J. (2012). Structural correlates for lexical efficiency and number of languages in non-native speakers of English. Neuropsychologia, 50(7), 1347-1352.
[18]. Kaiser, A., Eickhoff, S. B., Sobotta, L., & Menke, R. A. (2015). White matter structure in simultaneous interpreters: A DTI study. Neuroimage, 107, 190-200.
[19]. Hämäläinen, H., Sairanen, V., Kekki, M., & Lehtonen, M. (2018). The neural basis of language switching in multilinguals. Brain and Language, 179, 28-36.
[20]. Abutalebi, J., Canini, M., Della Rosa, P. A., Green, D. W., & Weekes, B. S. (2013). The neuroprotective effects of bilingualism upon the inferior parietal lobule: A structural neuroimaging study in aging Chinese bilinguals. Journal of Neurolinguistics, 27(2), 139-150.
[21]. Bialystok, E., Craik, F. I., & Luk, G. (2012). Bilingualism: Consequences for mind and brain. Trends in Cognitive Sciences, 16(4), 240-250.
[22]. Bialystok, E., Craik, F. I., & Freedman, M. (2007). Bilingualism as a protection against the onset of symptoms of dementia. Neuropsychologia, 45(2), 459-464.
[23]. Barac, R., Moreno, S., & Bialystok, E. (2016). Behavioral and electrophysiological differences in executive control between monolingual and bilingual children. Child Development, 87(4), 1277-1290.
[24]. Bialystok, E., Craik, F. I. M., & Luk, G. (2008). Lexical access in bilinguals: Effects of vocabulary size and executive control. Journal of Neurolinguistics, 21(6), 522-538.
[25]. Bialystok, E., Craik, F. I. M., Klein, R., & Viswanathan, M. (2004). Bilingualism, aging, and cognitive control: Evidence from the Simon task. Psychology and Aging, 19(2), 290-303.
Cite this article
Hu,K. (2024). Impact of Multilingualism on Brain Structure and Function: A Review. Theoretical and Natural Science,62,72-77.
Data availability
The datasets used and/or analyzed during the current study will be available from the authors upon reasonable request.
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References
[1]. Luk, G., De Sa, E., & Bialystok, E. (2011). Is there a relation between onset age of bilingualism and enhancement of cognitive control?. Bilingualism: Language and Cognition, 14(4), 588-595.
[2]. Mechelli, A., Crinion, J. T., Noppeney, U., O'Doherty, J., Ashburner, J., Frackowiak, R. S. J., & Price, C. J. (2004). Structural plasticity in the bilingual brain. Nature, 431(7010), 757-761.
[3]. Moreno, E., Marques, C., Santos, A., et al. (2015). Language control in bilinguals. Brain and Cognition, 94, 15-21.
[4]. Hernandez, A. E., Martinez, A., & Kohnert, K. (2000). In search of the language switch: An fMRI study of picture naming in Spanish-English bilinguals. Brain and Language, 73(3), 421-431.
[5]. Sebastián-Gallés, N., & Bosch, L. (2002). Building phonotactic knowledge in bilinguals. Language and Speech, 45(4), 289-316.
[6]. Perani, D., & Abutalebi, J. (2005). The neural basis of first and second language processing. Current Opinion in Neurobiology, 15(2), 202-206.
[7]. Li, P., Legault, J., & Litcofsky, K. A. (2014). Neuroplasticity as a function of second language learning: Anatomical changes in the human brain. Cortex, 58, 301-324.
[8]. Olsen, R. K., Pangelinan, M. M., Bogulski, C., et al. (2015). The effect of lifelong bilingualism on regional grey and white matter volume. Brain Research, 1612, 1-12.
[9]. Park, D. C., & Reuter-Lorenz, P. (2009). The adaptive brain: Aging and neurocognitive scaffolding. Annual Review of Psychology, 60, 173-196.
[10]. Berken, J. A., Gracco, V. L., Chen, J. K., & Klein, D. (2016). The timing of language learning shapes brain structure associated with articulation. Brain Structure and Function, 221(1), 359-370.
[11]. Reiterer, S., Pereda, E., & Bhattacharya, J. (2009). Measuring second language proficiency with EEG synchronization: How functional cortical networks and hemispheric involvement differ as a function of proficiency level in second language speakers. Second Language Research, 25(1), 77-106.
[12]. Ibrahim, R., Israeli, N., & Eviatar, Z. (2010). Hemispheric involvement in reading: The effects of language experience. Journal of Neurolinguistics, 23(2), 130-145.
[13]. Pliatsikas, C., Moschopoulou, E., & Saddy, J. D. (2017). The effects of bilingualism on the white matter structure of the brain. Proceedings of the National Academy of Sciences, 114(7), 1-5.
[14]. Burgaleta, M., Sanjuán, A., Ventura-Campos, N., Sebastián-Gallés, N., & Ávila, C. (2016). Bilingualism at the core of the brain. Structural differences between bilinguals and monolinguals in the basal ganglia. Brain Structure and Function, 221(5), 1-12.
[15]. Ressel, V., Pallier, C., Ventura-Campos, N., Díaz, B., Roessler, A., Ávila, C., & Sebastián-Gallés, N. (2012). An effect of bilingualism on the auditory cortex. Journal of Neuroscience, 32(47), 16597-16601.
[16]. Pliatsikas, C. (2020). Understanding structural plasticity in the bilingual brain: The contribution of diffusion MRI. Bilingualism: Language and Cognition, 23(2), 1-11.
[17]. Grogan, A., Parker Jones, O., Ali, N., Crinion, J., Orabona, S., Mechias, M. L., & Price, C. J. (2012). Structural correlates for lexical efficiency and number of languages in non-native speakers of English. Neuropsychologia, 50(7), 1347-1352.
[18]. Kaiser, A., Eickhoff, S. B., Sobotta, L., & Menke, R. A. (2015). White matter structure in simultaneous interpreters: A DTI study. Neuroimage, 107, 190-200.
[19]. Hämäläinen, H., Sairanen, V., Kekki, M., & Lehtonen, M. (2018). The neural basis of language switching in multilinguals. Brain and Language, 179, 28-36.
[20]. Abutalebi, J., Canini, M., Della Rosa, P. A., Green, D. W., & Weekes, B. S. (2013). The neuroprotective effects of bilingualism upon the inferior parietal lobule: A structural neuroimaging study in aging Chinese bilinguals. Journal of Neurolinguistics, 27(2), 139-150.
[21]. Bialystok, E., Craik, F. I., & Luk, G. (2012). Bilingualism: Consequences for mind and brain. Trends in Cognitive Sciences, 16(4), 240-250.
[22]. Bialystok, E., Craik, F. I., & Freedman, M. (2007). Bilingualism as a protection against the onset of symptoms of dementia. Neuropsychologia, 45(2), 459-464.
[23]. Barac, R., Moreno, S., & Bialystok, E. (2016). Behavioral and electrophysiological differences in executive control between monolingual and bilingual children. Child Development, 87(4), 1277-1290.
[24]. Bialystok, E., Craik, F. I. M., & Luk, G. (2008). Lexical access in bilinguals: Effects of vocabulary size and executive control. Journal of Neurolinguistics, 21(6), 522-538.
[25]. Bialystok, E., Craik, F. I. M., Klein, R., & Viswanathan, M. (2004). Bilingualism, aging, and cognitive control: Evidence from the Simon task. Psychology and Aging, 19(2), 290-303.