Brain and Language: Bilingualism: The Neural Basis of Processing More than One Language
In the last 20 years, research on neurolinguistics and bilingualism has demonstrated that exposure to two or more languages on a regular basis shapes individuals’ brain function and brain structure in ways that are different from those of monolinguals. Bilingual exposure enhances individuals’ brain plasticity and flexibility at higher levels than monolingual exposure; it also confers other benefits on the individuals.
What do monolinguals and bilinguals do similarly? Both groups mainly process language in the left hemisphere of the brain. Thus, linguistic information enters the brain circuitry through the auditory cortex in the temporal lobe when they listen. Wernicke’s area (BA39 and BA40) in the temporal lobe and Broca’s area (BA44 and BA45) in the frontal lobe are considered the classic language areas of the brain. These areas are inter-connected via various pathways and are both activated for speech comprehension and production.
Illustration 1 Brain circuitry for oral sentence comprehension (Friederici, 2012), including the temporal lobe (superior temporal gyrus and middle temporal gyrus) and frontal lobe (inferior frontal gyrus consisting of Broca’s area (BA44 and BA45)). Wernicke’s area (BA39 and BA40), not specified in the image, is a small area in the temporal lobe.
Once sounds are processed in the left middle portion of the Superior Temporal Gyrus (See Illustration 1), words are recognized and lexical-semantic integration takes place. Then sentential information travels to the frontal lobe for syntactic processing (in BA 44 and Frontal Operculum) and for further semantic processing (in BA 45 and BA 47) via different pathways. Ultimately, linguistic information goes back to the temporal lobe for semantic and syntactic integration and optimal sentence comprehension. This highly dynamic and interactive cycle occurs in both monolinguals and bilinguals when they process language; the pre-motor cortex is also activated when they articulate speech.
But what do bilinguals do differently from monolinguals? I highlight major research findings below:
Humans possess only one brain circuitry for language (Friederici, 2012- Illustration 1), and bilinguals need to use it to process their two languages. Researchers agree that bilinguals with proficiency in their two languages always activate their two languages (the dominant and the less dominant language) when they are using only one. This joint or parallel language activation occurs when they listen, speak, read and write in any of their two languages (Bialystok, Craik, & Luk, 2012; Costa & Sebastián-Gallés, 2014; Kroll, Gullifer, & Rossi, 2013).
As a result of this joint activation, the two languages are constantly interacting with, influencing, interfering with, and/or supporting one another in the bilingual’s mind. This interaction is bidirectional, from the dominant to the less dominant language and vice versa (Jasinska & Petitto, 2013; Kroll & Bialystok, 2013). As bilinguals become more proficient in their two languages, they also become more skillful at switching from one language to the other and at monitoring their two linguistic systems. Thus, they can easily select the grammatical structures and the vocabulary they want to use at a particular time while inhibiting the forms they do not need.
Both the joint language activation and the bidirectional language interaction shape bilinguals’ brain function and brain structure in ways that are different from monolinguals’:
As far as brain function is concerned, bilinguals and second-language learners show greater activation of the classic language areas in the brain (Broca’s area and Wernicke’s area) compared to monolinguals when they process language (Jasinska & Petitto, 2013). Furthermore, they reveal greater activation of the Left Dorsolateral Prefrontal Cortex (DLPFC) (Illustration 2-Jasinska & Petitto, 2013) and the Anterior Cingulate Cortex (ACC) (Illustration 3-Abutalebi et al., 2011), which regulate language switching and general executive functions such as conflict, control, monitoring, selective attention, and inhibition (Bialystok, Craik, & Luk, 2012; Costa & Sebastián-Gallés, 2014; Kroll, Gullifer, & Rossi, 2013). In fact, bilinguals and second language learners activate these cortices for linguistic tasks as they are constantly switching from one language to the other and monitoring their language use. Thus, their executive functions are enhanced and transfer to non-linguistic tasks such as those that require selective attention or inhibition. Overall, bilinguals’ ability to switch languages and manage executive control tasks well provides them with superior mental flexibility (Kroll & Bialystok, 2013).
Illustrations 2 & 3 The Left Dorsolateral Prefrontal Cortex (DLPFC) (Jasinska & Petitto, 2013) & The Anterior Cingulate Cortex (ACC) (Abutalebi et al., 2011)
As far as brain structure is concerned, lifelong bilingualism increases gray matter and white matter volume in the classic language areas, in regions involved in executive control such as DLPFC and ACC, and in the left inferior parietal region responsible for selective attention (Abutalebi et al., 2011; Bialystok et al., 2012; Christoffels, Kroll, & Bajo, 2013; Kroll & Bialystok, 2013; Kruchinina et al., 2012). Increase in gray matter density in the parietal region is positively correlated with second-language proficiency (Luk, De Sa, & Bialystok, 2011). White matter tracks become thicker in bilinguals than monolinguals because of their constant struggle to inhibit the unintended language while speaking and to switch linguistic and non-linguistic tasks (Christoffels, Kroll, & Bajo, 2013; Kroll & Bialystok, 2013). This increase in gray and white matter density enables bilinguals to build cognitive reserve, which refers to the ability to resist the damaging effects of dementia in old age. According to Kroll & Bialystok (2013), cognitive reserve delays the onset of dementia in bilinguals.
How distinctly do bilinguals process words, meanings, and syntactic structures from monolinguals? Like monolingual children, bilinguals learn words and meanings in their two languages through declarative memory or explicit learning (Ullman, 2005; Pujol, 2016). Research, however, has consistently shown that bilinguals often have a smaller vocabulary size in each language compared to their native counterparts (Bialystok et al., 2010; Conboy & Mills, 2006). Yet bilinguals’ total vocabulary size and their knowledge of translation equivalents in their two languages are positively correlated to their academic advancement (Bialystok et al, 2010; Conboy & Mills, 2006; Lindholm- Leary & Borsato 2006; Poulin-Dubois, et al, 2012), probably due to the interdependence of the two languages in the bilingual mind (Cummins, 1991).
Learning a second grammar after having acquired a first grammar (after the age of four) places serious demands on the brain for both grammars (Jasinska & Petitto, 2013; Ullman, 2005). The second grammar is not acquired in an unconscious, implicit way through procedural memory as children acquire their first grammar (Ullman, 2005; Pujol, 2016). Instead, it must be acquired in an explicit way through declarative memory. After sufficient instruction, understanding, and practice, second grammar rules can become automatic (Ullman, 2005). However, juggling two grammars will always involve more brain activation for bilinguals, even when they reach proficiency in their two languages (Wartenburger et al., 2003; Jasinska & Petitto, 2013).
Factors that influence bilinguals’ brain mechanisms when they process oral language include age of becoming bilingual, language exposure and use, language proficiency, and typological similarities and differences between bilinguals’ two languages (Kotz, 2009). The most influential factor is, of course, language proficiency (Abutalebi, Della Rosa, Ding, et al., 2013; Bialystok & Feng 2009; Iluz-Cohen & Armon-Lotem, 2013; Stein et al., 2012). Bilinguals with low language proficiency engage more extended brain areas when processing their weaker languages than bilinguals with high proficiency in their languages. The latter group engages similar brain areas and displays a stable overlap when processing any of their languages (Costa & Sebastián-Gallés, 2014;Wartenburger et al., 2003). This research illustrates the mental difficulties that beginning learners encounter when acquiring new vocabulary and grammatical structures in a second language.
To conclude, I would like to highlight a few classroom activities that not only support bilinguals’ brain functioning, but also facilitate their language acquisition. Educators can provide opportunities for vocabulary repetition, manipulation, elaboration, and review, always presented in meaningful contexts. Students should engage in conscious and explicit learning, analyzing grammatical and syntactic structures in depth, identifying similarities and differences, and making connections to prior linguistic experiences. Educators may also encourage students to reflect upon their language interference and language support instances as part of the learning process. This will increase students’ awareness and will strengthen their meta-cognitive and meta-linguistic skills. Finally, I would promote bilingual students’ literacy in their two languages. Learning English should undoubtedly be a priority for our bilingual students in the college, but there are different ways of learning a second language (Genesee et al., 2006; García, Pujol-Ferran, & Reddy, 2013; Pujol-Ferran et al., 2016). Brain research demonstrates that once a second language invades the brain circuitry, bilingual individuals’ brain function and brain structure start to change. This change is irreversible. Because the two languages are processed in such a highly intertwined manner in the brain, it is probably more feasible and comfortable for the learners to reach proficiency in their two languages than in only one; they will be well equipped to monitor their language use and will eventually enjoy the many benefits of bilingualism (García, 2009; Kroll & Bialystok, 2013). Therefore, I believe that educators should explore ways to assist bilingual students in developing their full bilingual potential.
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Language and Cognition Department
Mercé Pujol-Ferran is a Professor in the Language and cognition Department at Hostos Community College, where she teaches ESL and Linguistics courses. She has also been an Adjunct Associate Professor in the Department of Cognitive Studies in Education and Developmental Psychology at Teachers College, Columbia University in New York, for a decade; she teaches a Psycholinguistics course. Professor Pujol has done research and published on the acquisition of English by immigrant Latino students, on XIX century Catalan female poetry, and most recently on plurilingual pedagogies across the college curriculum. Sha has also been doing research on the neurolinguistics of bilingualism and multilingualism.