Who hasn’t fantasized about learning a new language or acquiring a skill while fast asleep? After all, why “waste” your time sleeping, especially if you can increase your knowledge with no effort whatsoever, right?
Sleep learning is such a compelling concept that many a business has sprung up to promote it. “Reclaim a third of your life for self-improvement, learning, and personal enrichment!” promises the Official Sleep Learning website. By listening to its “specially prepared CDs” while unconscious, you can not only learn a new language but also find greater self-esteem, overcome allergies, improve your golf game, and better yourself in a host of other ways.
Unfortunately, the premise that the mind can be “reprogrammed” in sleep is as unproven today as it was in 1927, when Czech-born businessman and inventor Alois Benjamin Saliger introduced his Psycho-phone. The repeating phonograph was meant to sit by the sleeper’s bed and whisper inspiring messages through the night. “I desire an ideal mate,” Saliger whispered on a disk titled “Mating.” “I radiate love. I have a fascinating and attractive personality. I have a strong sex appeal.” Upon awakening, the sleeper would presumably be ready to assert his appealing self and find the partner of his dreams.
In the years since, science has debunked the idea of learning while sleeping—or “hypnopaedia,” as Aldous Huxley called the technique in his dystopian 1932 novel Brave New World—but there is a connection between sleep and our ability to learn and retain new information. Here’s a look at what scientists know about our sleeping brains.
Sleep’s role in learning
In the 1950s, scientists began using electroencephalography (EEG) to measure the brain’s electrical activity. By attaching electrodes to a sleeper’s head, they were able to determine when subjects were actually asleep rather than near sleep or merely resting. They soon rejected the notion of sleep learning, or that people were learning anything new while they were actually sleeping. A famous 1956 EEG study concluded that sleep learning was “impractical and probably impossible.”
What they discovered was that sleep has two core stages—slow-wave sleep (SWS), or deep sleep, and rapid eye movement (REM) sleep. By the mid-1990s, research was suggesting that each of the sleep stages plays a specific role in memory. During deep, dreamless SWS, which predominates in the early part of sleep, the brain processes and consolidates memories. The brain’s hippocampus serves as a temporary memory storehouse, like a computer’s clipboard, before scientists believe REM sleep, which becomes more intense toward the end of the sleep cycle, organizes and stores memories in the prefrontal cortex.
Although learning while you sleep is unlikely, research shows that sleep is necessary to learning and memory. A sleep-deprived person can’t optimally focus attention, a prerequisite of learning. And sleep itself appears to be required to consolidate memories and retain them for the long term. (Take our sleep deprivation quiz to see if you need to aim for more shut-eye.)
“When we first form memories, they’re in a very raw and fragile form,” says sleep expert Robert Stickgold, PhD, of Harvard Medical School. “Sleep seems to be a privileged time when the brain goes back through recent memories and decides both what to keep and what not to keep.”
What the sleeping brain can learn
Based on a deeper understanding of the brain’s activity during sleep, more recent studies suggest that some types of sleep learning may in fact be possible. But it’s important to look at what is learnable, and how and when it’s learned.
A 2017 study reported in Nature Communications found that a group of 20 subjects were able to recognize patterns of sound embedded into clips of white noise after the 200 millisecond-long clip was repeated five times as they slept.
It’s not quite like learning a new language, but neuroscientist Thomas Andrillon, one of the study researchers at PSL Research University in Paris, said, “the sleeping brain is including a lot of information that is happening outside, and processing it to quite an impressive degree of complexity.”
The scientists discovered that the white-noise memories formed only during REM and light sleep; subjects couldn’t remember the pattern of sounds when they were played during non-REM sleep. This was the first time they had evidence that particular sleep stages are involved in forming completely new memories.
Although learning a white noise sound pattern offers no practical value, other studies suggest that some things learned during waking hours may be enhanced during sleep when reinforced with sound.
In one experiment, scientists had native German speakers learn some basic Dutch vocabulary words and then go to sleep. While one group slept, the researchers played some of those words. When tested later, the group that had listened to them overnight could better identify and translate them.
Researchers in another study taught subjects to play guitar melodies using a technique from the video game Guitar Hero before going to sleep. The scientists played the same melody for one group as they slept. Even though they didn’t remember hearing it, the group that heard the melody as they slept played it much better than those who didn’t hear it.
Another sensory organ, the nose, was used in 2007 research at Lübeck University to test whether odors could be used to stimulate the sleeping brain. Researchers exposed some study participants to the scent of roses as they taught them the locations of objects on a grid. As they slept, the experimenters again exposed them to the rose scent during SWS.
Those who had been exposed to the rose scent while learning the object locations were significantly better at remembering where the objects were located than subjects who hadn’t been exposed to it while they were initially learning it.
There still are open questions as to whether using sounds or smells to cue memories is effective for doing more than reinforcing what was already learned during waking. Could they be used to help learn grammar, or only foreign vocabulary words? How about using them to maintain memory performance among aging people? Does selectively reinforcing some memories mean others are not being fully processed and are eliminated?
“During sleep, humans can strengthen previously acquired memories,” said researchers from the Weizmann Institute of Science in a 2012 Nature Neuroscience report, “but whether they can acquire entirely new information remains unknown.”
The risks of sleep learning
What does seem certain is that the brain requires sleep to do its job. We already know that sleep deprivation hinders our ability to function at our best. But what happens when we start fiddling with the normal processes by which our brains sort and store what we learn in our memory banks?
Could sleep learning disrupt sleep’s restorative function? Does keeping the brain actively absorbing new information during sleep distract it from consolidating long-term memories of things learned during our waking hours? On a jarring note, would disrupting the brain’s routine sleep-time housekeeping increase the sleep learner’s vulnerability to neurodegenerative diseases like Alzheimer’s?
It may seem appealing to hook up an EEG app to our smartphones with the aim of improving ourselves effortlessly while we sleep. but there may be a cost to this nocturnal multitasking. Noting that every animal in the world sleeps, whether a gnat or a human, neuroscientist and sleep researcher Sid Kouider of the Ecole Normale Supérieure in Paris cautioned, “Research focusing on how to take advantage of our sleeping time must consider what is the associated cost, if any, and whether it is worth it.”