Breaking from a conversation in Spanish and turning it into a discussion in German is a two-step process that requires a degree of cognitive effort.
Until now, researchers have never been sure which part required more work: ending the first language or starting with the second. A new study reveals just what's going on upstairs when we make a switch between languages.
"A remarkable feature of multilingual individuals is their ability to quickly and accurately switch back and forth between their different languages," says study lead author Esti Blanco-Elorrieta from New York University.
This isn't limited to Spanish and German, or even verbal languages. People who flip from sign languages to spoken word also appear to seamlessly blend one stream of thought into another.
But just how seamless is this process?
The anterior cingulate cortex helps us pay attention, while the pre-frontal cortex is the 'thinking' part of the brain, what we generally associate with decision making and other executive functions.
So it probably comes as no surprise that when we decide to switch between two languages, we might involve parts of the brain that look at what's happening around us and evaluate outcomes before flipping the switch.
This jump in neural activity suggests the brain needs to work harder to move from one language to another. Far from a smooth transition, it's clear there's some hard peddling going on.
What hasn't been clear is precisely what drives this change. Are we peddling to shut one mental language book, or open another? The two actions are virtually simultaneous, which makes them hard to tease apart.
One way to pinpoint the ultimate cause of this neural activity would be to look at the brain as it starts one language without stopping the first.
Breaking into English without pausing your Spanish monologue would require a second mouth, so we can forget two spoken languages. Instead, the research team turned to individuals who could English and American Sign Language, or ASL.
"The fact that they can do both at the same time offers a unique opportunity to disentangle engagement and disengagement processes – that is, how they turn languages 'on' and 'off'," says Blanco-Elorrieta.
The experiment itself involved naming images shown on flash cards, while having the magnetic fields of their brains mapped in a procedure called magnetoencephalography.
Repeating the process with 21 native ASL-English speaking volunteers – all children of deaf parents – provided the team with enough data in detailed resolution to identify the exact moment key areas of the brain kicked it up a notch.
It turns out we need to work at putting the brakes on one language, but don't really need to do much to get our fingers and tongues wagging on the second.
"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.
Surprisingly, this meant that it didn't really take any more effort to name an image in ASL and English at the same time than it did to name it in just ASL. Naming it in English alone, however, was relatively easy compared to both.
Learning more about the neurology of bilingualism is an important field. Brains that can jump between different languages often have a slight cognitive edge on those that can't. Having a second language on call might even help you recover faster from a stroke.
If this study shows us anything, it's that our brains find it relatively easy slipping from one language to the next. Just as long as you can put the brakes on your babble first.
This research was published in PNAS.