New research with speakers of English and American Sign Language (ASL) reveals the processes that go on in our brain when switching between languages.

Street signs with Latin and Cyrillic letters in Kirkenes, Norway.
Image credits Wikimedia.

It seems that our brain has to ‘boot up’ a language before we can start speaking it. Previous research has identified spikes in brain activity in areas associated with cognitive control (i.e., the prefrontal and anterior cingulate cortices) when this switch is performed. However, whether this activity was required to ‘activate’ a new language, turn a previous one off, or both, remained unknown. Now, a team of researchers has uncovered the mechanisms that underpin switching between different languages, a finding that provides new insights into the nature of bilingualism.

Speaking in tongues

“A remarkable feature of multilingual individuals is their ability to quickly and accurately switch back and forth between their different languages,” explains Esti Blanco-Elorrieta, a New York University (NYU)Ph.D. candidate and the lead author of the study. “Our findings help pinpoint what occurs in the brain in this process — specifically, what neural activity is exclusively associated with disengaging from one language and then engaging with a new one.”

The results showed that cognitive effort is required primarily when disengaging from one language — activating a new one, by comparison, comes virtually “cost-free from a neurobiological standpoint,” says senior author Liina Pylkkanen

The biggest hurdle in this research effort was to separate the two process because they largely happen at the same time. For example, a Spanish-English bilingual participant would turn Spanish “off” and English “on” at the same time. To work around this issue, the team recruited participants fluent in English and American Sign Language (ASL) and asked them to name the pictures on the screen.

Unlike other language combinations, English and ASL can be spoken together at the same time — and they often are. This dynamic gave the team the tool they needed to separate the language engagement and disengagement processes in the brain. They could ask the participants to go from speaking in both languages to producing only one to observe the process of turning a language ‘off’. Alternatively, participants could be asked to switch from speaking only one language to speaking both — giving the team a glimpse of the process of turning a language ‘on’.

In order to actually see what was going on in the participants’ brains, the team used magnetoencephalography (MEG), a technique that maps neural activity by recording magnetic fields generated by the electrical currents produced by our brain.

When the bilingual English-and-ASL participants switched between languages, deactivating a language led to increased activity in cognitive control areas. Turning a language ‘on’ was virtually indistinguishable from not switching, judging by brain activation levels, the team writes. In other words, little to no cognitive effort is required to activate a second language, be it spoken or signed language.

In fact, the team reports that when participants were asked to produce two words simultaneously (one sign and one spoken word), their brain showed roughly the same levels of activity as when they only produced one word. Most surprisingly, producing both at the same time saw lesser activation than having to suppress the dominant language (in this case English).

“In all, these results suggest that the burden of language-switching lies in disengagement from the previous language as opposed to engaging a new language,” says Blanco-Elorrieta.

The paper has been published in the journal Proceedings of the National Academy of Sciences.