Bilingual Brains: Function, Structure, and Neuroimaging

The mere existence of those who speak multiple languages raises many questions in terms of brain structure and function. Namely, how do people acquire new languages and, once acquired, where does the brain ‘place’ these languages? Furthermore, does language processing happen in the same place for all of a polyglot’s languages? Luckily, today’s neuroimaging tools provide us with a non-invasive way of answering these questions. Firstly, we must consider what we know of the bilingual brain without the use of neuroimaging. It has already been observed that bilingual people suffering from aphasia (an inability or difficulty in comprehending and formulating language due to a stroke or other brain-related trauma) did not always suffer its effects in the same way for each language. This suggests the possibility that bilingual brains ‘store’ languages in different parts of the brain at least some of the time. It is also already known that early on in language learning the second language is processed by a sort of translation from the first language and that as proficiency is gained the use of the second language becomes a more fluid and unconscious process. Functional neuroimaging processes like positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) now allow us to directly observe these processes in action thus understanding why and how they occur (Perani 2003).

There is no question that being bilingual effects the structure of the brain and can be beneficial to the health of the bilingual speaker. The below image displays the regions with higher activation and higher white-matter integrity in bilinguals.

Figure 1. Effects of Bilingualism on the Brain. Green depicts grey matter regions that show high activation during bilingual language switching, red-yellow depicts areas of higher white matter integrity in bilingual adults as compared to monolingual adults. (Bialystok 2012)

These structural differences have long been attributed to the repeated finding that bilinguals have better working memory and better ability to switch attention/tasks. It has also been shown that bilinguals activate the regions of their brain that speak either language no matter what language is being utilized. It is this joint activation that creates what is known as higher neuroplasticity in polyglots, also contributing to lower rates and later onset of dementia in bilinguals (Bialystok 2012).

These structural differences in the separation of languages in bilinguals have been physically observed. A 2004 study mapped the functional separation of languages by electrical stimulation. The research finds that language-specific sites exist in all speakers. However, in 60% of bilinguals, their language use was contained not in one language site, but two. Furthermore, it was found that language production resulted from the use of not only language-specific sites but also shared sites. This means that bilingual brains have physical areas dedicated to respective languages separately, but that there is also an overlap in the use of these areas (Lucas 2004).  This lends physical evidence to the belief in bilingual neuroplasticity in that bilinguals undoubtedly get more use, and more varied use, of certain parts of their brains. Furthermore, a 2006 study used fMRI imaging to exactly place where it is in the brain that bilinguals control language processing. The study concludes that the left caudate (see Figure 2) “plays a significant role in language control”. In essence, it is the left caudate that controls which of the previously mentioned language specific sites are activated and how they interact, allowing the bilingual to speak two distinct languages. (Crinion 2006)

Figure 2. Location and activation of the left caudate. Bilinguals were presented semantically related word pairs in two different languages and it was the left caudate that showed most activity, meaning it may be this region that controls language-switching.

Unfortunately, research has also been done to show that bilingualism may effect the speaker’s ability to separate languages. A 2005 experiment asked bilingual patients to press a button if the name of the object shown to them started with a vowel but not with a consonant, and vice versa. Specifically, in this experiment patients were speakers of German and Spanish. A control group of monolingual German or Spanish speakers was also tested. It was found that bilinguals made more mistakes in their answers and their responses were slowed by about 100 to 200 milliseconds. This was timed physically and by fMRI imaging (Rodriguez-Fornells 2005).  It can be inferred that this delay is a consequence of the language-specific sites and shared sites that are used simultaneously in bilinguals, as shown in the previous study. However, a 100 to 200 millisecond delay in response does not quite constitute a worrisome consequence of being bilingual, especially in light of all of its benefits. The results of all of these studies, while they answer many questions, warrant further exploration into the structure and function of bilingual brains. Moreover, questions about the function and structure of the brains of those who speak more than two languages has not been explored.

References

Bialystok, E., Craik, F. I., & Luk, G. (2012, April). Bilingualism: Consequences for Mind and Brain. Trends in Cognitive Science, 16(4), 240-248. Retrieved October 30, 2016.

Crinion, J., Turner, R., Grogan, A., Hanakawa, T., Noppeney, U., Devlin, J., . . . Price, C. (2006, June 9). Language Control in the Bilingual Brain. American Association for the Advancement of Science, 312, 1537-1540. Retrieved October 30, 2016.

Lucas, T. H., II, McKhann, G. M., II, & Ojemann, G. A. (2004, September). Functional Separation of Languages in the Bilingual Brain: A Comparison of Electrical Stimulation Language Mapping in 25 Bilingual Patients and 117 Monolingual Control Patients. Journal of Neurosurgery, 101, 449-457. Retrieved October 30, 2016.

Perani, D. (2003). Functional Neuroimaging and the Bilingual Brain. Friulian Journal of Science, 4, 115-131. Retrieved October 30, 2016.

Rodriquez-Fornells, A., Van der Lugt, A., Rotte, M., Britti, B., Heinze, H., & Münte, T. F. (2005). Second Language Interferes with Word Production in Fluent Bilinguals: Brain Potential and Functional Imaging Evidence. Journal of Cognitive Neuroscience, 17(3), 422-433. Retrieved October 30, 2016.