Learning Language in Deep Sleep Isn't Just Science Fiction Anymore

As important as sleep is for health, happiness, and performance, it really is a time suck. Those eight or so hours when we lose consciousness may be restorative, but just think of what we could accomplish if we could actually put them to productive use. Scientists believe that we can use these unconscious hours to begin to learn new facts or languages in our sleep, as long the information is presented in the right way.

In his paper published Thursday in Current Biology, University of Bern neuropsychologist Marc Züst, Ph.D., presents evidence that it’s actually possible to form new “semantic connections” at specific moments during the sleep cycle. These, he explains, are associations between two words that we use to help encode new information and give words context. For instance, when we hear the word “winter,” we think of cold temperatures, skiing, or, most recently, polar vortices. In his study, Züst found that the brain can actually learn to make these associations if we hear two words paired together at certain times within the sleep cycle.

“Humans are capable of sophisticated information processing without consciousness,” Züst tells Inverse. “Sleep-formed memory traces endure into the following wakefulness and can influence how you react to foreign words, even though you think you’ve never seen that word before. It’s an implicit, unconscious form of memory — like a gut feeling.”

In his study, Züst, working alongside neuropsychologist Katharina Henke, Ph.D., attempted to teach his study participants new words in an invented language. This way, he could ensure that no one had any previous memory of the words. All through the night, his sleepers heard repetitive word pairings featuring a made-up word like “aryl” and that word’s “translation” — in the case of “aryl,” “cork.” When they woke up, Züst tested their knowledge of these pairs and found that, though the participants had never consciously studied the language, he found that they had a sense of what the word meant.

"“It’s an implicit, unconscious form of memory — like a gut feeling."

“If you are provided with a clear context or associated concept, like ‘aryl equals cork,’ your brain can integrate this new word into the semantic network and associate it with wine tasting, being a small object, sticking notes to a board, and so on,” says Züst. “The word gets a meaning.”

While this technique probably won’t help you pass any tests, Züst explains that the concept behind his study suggests that the brain is more aware of external stimuli during deep sleep than we previously believed. Earlier theories indicated that when we enter deep stages of sleep, certain areas of the brain are focused on consolidating memories, shutting out external stimuli to accomplish that task. In the paper, the team indicates that there are actually small windows of time when the brain is “open” to learning new information during deep sleep periods.

He explains that the cells in our brain have roughly cyclical firing patterns during deep sleep. Over the course of a second, they oscillate into an up-state, when they fire together, and then into a down-state, when they’re relatively silent. During those up-states, which last about half a second, Züst believes that the brain is open to receiving new information and making new connections, like assigning meaning to an unfamiliar word. But to actually help the brain make those connections, you really have to hit that specific window. “The more often word pairs hit up-states, the better the memory,” he adds.

As promising as this is for all of us ready to turn sleep into the ultimate 8-hour multitasking session, Züst cautions that we don’t know how pumping the brain full of new information during up-states might impact what it’s actually trying to accomplish during that period — resting, recharging, and consolidating all the information we took in during the day. Over the course of time, these learned associations may actually impede that function. His study didn’t investigate those possible consequences.

At this point, Züst advises that we should proceed with caution when it comes to trying to cram new information into our already-hard-working brains. His results should put us on alert, he notes: You might not be the only person competing for a time slot in the brain’s unconscious, but crucial, up-states.

“It is good to know that you aren’t completely shut-off from your surroundings while asleep, especially if you’re prone to falling asleep in front of your TV,” says Züst. “Imagine listening to commercials all night. Some of that information could stick, and you would never know.”

Abstract: Learning while asleep is a dream of mankind, but is often deemed impossible because sleep lacks the conscious awareness and neurochemical milieu thought to be necessary for learning. Current evidence for sleep learning in humans is inconclusive. To explore conditions under which verbal learning might occur, we hypothesized that peaks of slow waves would be conducive to verbal learning because the peaks define periods of neural excitability. While in slow-wave sleep during a nap, a series of word pairs comprising pseudowords, e.g., “tofer,” and actual German words, e.g., “Haus” (house), were played to young German-speaking women and men. When the presentation of the second word of a pair (e.g., “Haus” of “tofer-house”) coincided with an ongoing slow-wave peak, the chances increased that a new semantic association between the pair had been formed and retained. Sleep-formed associations translated into awake ones, where they guided forced choices on an implicit memory test. Reactivations of sleep-formed associations were mirrored by brain activation increases measured with fMRI in cortical language areas and the hippocampus, a brain structure critical for relational binding. We infer that implicit relational binding had occurred during peaks of slow oscillations, recruiting a hippocampal-neocortical network comparable to vocabulary learning in the waking state.