Multilingualism is more common than you might think, as more than half of the world’s population speaks more than one language. 

Have you ever watched two bilingual people converse in two distinct languages, switching in and out during the conversation, or even during a sentence? Maybe this is how you communicate with your family at home. But have you ever inquired how the brain can accomplish this? 

Understanding the brain’s ability to switch back and forth between languages raises important neurobiological and linguistic questions that require us to invest our time and resources to answer. In linguistics, the phenomenon of being able to shift from one language to another during a conversation, or even within a sentence, is called “code-switching.” 

The bilingual advantage

It is a common belief that those who speak multiple languages possess a cognitive advantage, that is, a superior ability in how they register and process environmental stimuli. Picture this scenario: you are fluent in both English and French. However, you are speaking to an individual who only knows French. While speaking, you must be capable of repressing your knowledge of English so that you are only verbally expressing yourself in French. 

Researchers have proposed the “adaptive control hypothesis” to explain how individuals who speak multiple languages can inhibit information in one language to use another language in a conversation. This skill requires more effort from the brain and thus leads to strengthening the anterior temporal lobe and the ventromedial prefrontal cortex, regions of the brain that play a role in memory abilities. 

But is this hypothesis supported by neurobiology research?

Neurobiological mechanisms for code-switching

A 2021 study by Sarah F. Phillips and Liina Pylkkänen investigated whether there is an association between the brain’s temporal lobe and prefrontal regions during code-switching. 

While previous studies have shown that the left anterior temporal lobe is responsible for composing words, it was unclear how the temporal lobe — responsible for processing sensory information, regulating emotions, restoring and recalling memory, and understanding language — plays a role in code-switching. Furthermore, although the prefrontal regions of the brain have been associated with code-switching, neuroscientists lacked further information about the exact role they play in this process. 

In their study, Phillips and Pylkkänen used magnetoencephalography (MEG) measurements in 20 bilingual individuals fluent in English and Korean. MEG is a noninvasive neuroimaging technique used to measure brain activity. 

English and Korean are “typologically distant” languages, meaning they have different grammatical patterns. Phillips and Pylkkänen conducted tests for both spoken language and orthography — the conventional spelling system of a language. To assess the participants’ orthographical abilities in both languages, they conducted two tests, the COMP test — where they assessed participants’ speed at matching a picture to a two word-sentence — and the LIST test — where they assessed the speed of matching the picture to one word of a two word-list. 

While there were no discrepancies in participants’ response time and accuracy when switching between spoken languages, there was a decrease in reaction time in the COMP test and accuracy in the LIST test when switching orthography. 

Brain regions involved in code-switching

The MEG results of the study showed that the brain’s anterior cingulate cortex and left inferior frontal gyrus are active during language processing and interpretation. In addition, the anterior temporal lobe and the ventromedial prefrontal cortex are active when an individual switches between languages. The study revealed activity in all four of these regions when participants switched between different languages for speaking and orthography. This not only indicates that these regions are relevant for both speaking and orthography, but that there is coordination between them during both processes. 

Overall, this study helps us understand how multilingual people can switch back and forth between languages. The underlying mechanism identified to explain this ease lies within the left anterior temporal cortex and its ability to interpret language equally, even when an individual switches between languages. 

Language switching does not get processed in the brain until after the switch has occurred, revealing how natural this phenomenon of multilingualism truly is. These findings reveal that code-switching is seamless, and the patterns of activity found within the brain regions of individuals switching from one language to another are parallel to the patterns of brain activity found in individuals continuously speaking one language.