Can you learn a new language while you sleep?

Although I can casually pepper my speech with common conversational phrases in other languages (bien sur!) I’ve never actually become fluent in any language but English. Yes, I’m interested. Yes, I’ve tried Duolingo. And yes, I have taken classes. But none of my feeble attempts have helped another language take hold in my brain. So, when I heard murmurs about the potential of learning another language in my sleep, I was immediately curious. It sounds far-fetched — but could it be possible?

First of all, many of us assume that the brain just sort of shuts off or plays reruns during sleep. That’s not exactly the case, although it does process memories (which could be compared to reruns) while we sleep. When we’re in deep sleep — also called Slow Wave Sleep (SWS) — the brain goes through the memory traces that were created during wakefulness and strengthens the important ones, while unimportant ones are weakened or deleted to make room for new learning the next day, explains Marc Züst, a professor of psychology at the University of Bern in Switzerland, who studies sleep and learning.

During SWS, the brain is more or less active in waves — called up-states and down-states — that last for about half a second each. Züst and some of his colleagues were intrigued by research that suggested that our brains are able to process and retain information during SWS. So, they wondered, if our brains can use this time to digest and hold information, is it possible that we could learn new things while we sleep, as well? “We hypothesized that up-states constitute windows of opportunity to learn new information during slow wave sleep,” says Züst.

Züst, along with his fellow researchers Katharina Henke and Simon Ruch, decided to find out. Their 2019 study examined whether people could learn new words in a foreign language during the up-states. Here’s how it worked: Individuals were given headphones to wear while they slept. Recordings were played in which words were spoken in a made-up language, followed by their translation in German — the participants’s native language during the up-state.

If that seems too abstract, imagine that someone says, “Tofer" means "key,” and "Guga" means "elephant.” These words aren’t real, but that doesn’t matter. What matters is that your brain forms an association between the sound of the new word and the meaning. And the participants did just that. Kind of.

When participants were awake, they could remember, for example, that a “guga” was bigger than a “tofer.” Amazing, right? Definitely, amazing, but the whole “we can learn a language in our sleep thing” has its caveats. “While this can potentially be used to boost vocabulary acquisition, learning a whole new language is much, much more complex than that,” Züst says.

What the study actually shows, Züst explains, is that the brain can create associations between words during sleep — that’s not the same as learning a whole language. Learning grammar, for example, requires the brain to analyze complex sentence structures, says Züst, which is necessary for learning a language and which you cannot, unfortunately, do in your sleep. Also, he explains, “we are physiologically limited as to how much we can present to the brain during SWS,” meaning there’s only so many words you can fit into a half second long up-state, and that’s the sleep wave you need to ride to make those linguistic associations.

Also, the state of consciousness you’re in when you receive information makes a difference in how you recall it. Züst explains that that’s another reason why you can’t functionally learn a language asleep. “The information presented during SWS enters the brain unconsciously, and you will not be able to consciously access it afterwards,” he says. “We had to use some tricks to get to the information after waking. We used a test for implicit memory, where participants had to ‘trust their gut feelings.’ We showed them all the foreign words we presented during sleep again, but they thought they were seeing these words for the first time, and just guessed if those were large or small objects.” Guessing is what I already do when I’m trying to speak another language, so that’s not actually that helpful.

“There is, unfortunately, no shortcut to learning a new language through sleep,” says Züst, “You will still have to do that with some conscious effort.” Your effort may be ballasted by some subconscious recordings, he explains, but this idea has really only been tested in clinical conditions and sophisticated equipment. “The notion of turning on a tape player and shutting your eyes to wake up fluent is both tempting and absurd,” says Elizabeth Lombardo, a psychologist based in Chicago. Wamp wamp. When I mentioned to Züst that some psychologists feel like the whole idea of learning a new language in your sleep seems a little sus, he said, “Those psychologists are right.”