It has long been known that sleep is essential to the learning process. While our bodies are tuned down for eight hours of rest, our mind is hard at work, taking the information we’ve learned throughout the day and storing it within our mind’s brimming bank of knowledge and memories.

Just what mechanisms are involved in this process still seems unclear, but many are beginning to tap into the potential of learning while you sleep. The key here is to take the information we’ve absorbed during the day, and relearn it during sleep, so that the next day the info is as fresh as if we had spent all night studying it.

What is Memory and How Does Sleep Play a Role?

To fully understand this, it’s important to note how the mind processes memories during sleep, and which stages of the sleep cycle are involved. When it comes to learning and memory, there are three main components to having something new sink into our brain. The Harvard Medical School details them as acquisition, consolidation, and recall. Acquisition occurs when we are introduced to new information; consolidation involves the stabilization of this information, usually into long-term memory; and recall is the ability to access the information later on. Whether or not we can actually acquire new memories during sleep is up for debate (more on that later) but throughout our resting time, we do know a whole lot of consolidation is happening.

“During sleep, recent memories, such as those of that day, are transferred to the higher cortical centers where they are consolidated into long term memories,” Dr. Robert S. Rosenberg, board certified sleep medicine specialist and author of Sleep Soundly Every Night, Feel Fantastic Every Day, told Medical Daily. “There are different types of memories and their consolidation into the brain’s hard drive for permanent storage occurs at different stages of sleep.”

The three types of memories we consolidate in sleep are declarative (fact-based information), emotional, and operational, which includes skills like learning to ride a bike or play a song. “We believe that declarative memories, such as fact figures and episodic memory occurs during slow wave sleep. Emotional memory processing, which involves the emotional center, the amygdala, and the prefrontal cortex, as well as operational memory… seems to occur during REM sleep,” Dr. Rosenberg said.

According to Dr. Jose Colon, neurologist, sleep doctor, and founder of Paradise Sleep, REM sleep is essential to the consolidation process, while slow wave sleep helps to restore our brains to take in new memories the next day. “Many people think that REM is our deep sleep, but it’s a very active brain time that we take in the day’s information and we’re turning it into a long-term memory,” he told Medical Daily. “Slow wave sleep is the part that washes away your exhaust and the metabolism waste products so your mind is refreshed for the next day.”

Even though we are not 100 percent sure how it works, researchers are still trying to determine how we can make memorization in the middle of the sleep possible. So far, it seems to be working.

Memorizing a language while you snooze

You’ve probably heard of those language tapes that you play while you sleep. Go to bed knowing only one language, wake up bilingual. Well, a team of Swiss researchers put this method to the test to see if learning a language while asleep was a sound possibility.

For the study, two groups of native German speakers were given a list of Dutch-to-German words to memorize at 10 p.m., right before they went to sleep. Researchers then told one group to hit the hay, while they kept the other awake. Both groups were exposed to audio of some of the words they learned, along with new ones, over the next few hours. Researchers were careful to make sure that those who were asleep were listening to the recording during non-REM sleep, or slow wave sleep, which is when declarative memories are consolidated. They made sure the participants didn’t wake up during this stage of the experiment, but how?

Dr. Jesse Mindel, a neurologist from Ohio State University believes he has the answer. “It’s hard to give someone information without causing them to wake up. Most of the stimuli they’re giving people when they’re sleeping is sub-threshold… something like a light sound, or a touch that improves memory or alters sleep in a positive way,” he said. Sub-threshold stimuli have the ability to expose individuals to information (hopefully) without causing disruptions to sleep, thus allowing the consolidation process to continue.

At around 2 a.m., researchers tested both groups on how many words they could remember. It turns out that the group that had been listening to the recording during slow wave sleep was able to recall words they had learned before they went to sleep better than the group that remained awake. The words they did not know but heard while sleeping did not seem to stick.

Interestingly enough, when researchers observed sleeping participants’ brains with EEG scans, they saw theta brain waves being emitted while the snoozers listened to the tape. Theta waves are known to emerge during  heightened states of learning, which usually occur during waking hours, suggesting that some level of learning was happening.  

This technique, which researchers call “verbal cueing,” can be done by anyone, as long as the language recording is played within the first few hours of sleep (aka the time when we’re in slow wave sleep). Also, the recording must feature words that you have already been exposed to, because the study did not find new words could be learned during sleep.

Dreams of being Mozart can be a waking reality

In a similar study from 2012, Northwestern University neuroscientists found that slow wave sleep can affect your ability to learn to play a song. For their experiment, two groups of participants were given diagrams displaying how to play two different songs on the piano, each with 12 notes. Researchers gave the participants an equal amount of time to practice, and then told them to take a 90 minute nap.

While the participants were sleeping, the researchers played the first melody for one group, and the second for the other. Upon waking up, participants were asked to  play the song they heard in their sleep. The team observed that those who listened to the melody while they were asleep were able to play it four percent more accurately than the song they didn’t listen to. What’s more, they found that the longer participants slept, the more accurately they were able to play the song they were listening to while sleeping.

Like the language study, an EEG scan revealed spindle waves coming from participants’ brains while sleeping and listening to the song. Spindle waves are thought to be associated with memory processing, and helping with hand motor skills. Most importantly, researchers suggested that this type of memory cueing occurs when someone is exposed to information through sound during sleep — although other studies have found exposure to scents can affect memory cueing as well.

Can We Actually Learn Something New in our Sleep?

The only way to answer this question right now is maybe. Though many believe memory acquisition cannot occur during sleep, a recent study conducted by researchers at the Weizmann Institute of Science has found otherwise. To test the possibility of learning new associations while sleeping, researchers played a tone, and then presented participants with either a pleasant or unpleasant odor. They then played another tone and accompanied it with an odor opposite from the first. They continued to alternate throughout the course of the night in order to reinforce the associations. They observed that the tone would provoke participants to breathe deeply in their sleep if the associated odor was pleasant, while they breathed in short sniffs when the tone came with a bad smell.

The researchers played the tones again when the participants woke up, this time without the accompanying odors, and found that participants would still sniff in short or deep breaths, depending on what the odor was associated with. The researchers concluded that because this association was not developed beforehand, while the subject was awake, they acquired this association while asleep.

Moreover, the researchers found that this association was solidified during REM sleep, and not slow wave sleep, as the previous experiments had found. They suggested that the “dream amnesia” that occurs in slow wave sleep, which makes us forget our dreams may play a part in why we forget new memories as well.

These studies have the potential to guide future research. Alzheimer’s patients, for example, get significantly less slow wave sleep, which may contribute to memory decline. “That’s kind of the future of this,” Mindel said. “Can you modify the disease process?”

Source: Schreiner T, Rasch B, et al. Boosting Vocabulary Learning by Verbal Cueing During Sleep. Oxford Journals. 2014.

Anthony J, Goebel E, O’Hare J, et al. Cued memory reactivation during sleep influences skill learning. Nature. 2012.

Azri A, Sobel N, Nasser K, et al. Humans can learn new information during sleep. Nature. 2012.