Many of us spend about one-third of our lives sleeping or trying to. We may be doing a lot more during that time than just drifting into the land of nod. A recent study in Nature Communications suggests sleep can enhance the brain's ability to learn new information by boosting memory recall when we wake up.

Researchers from PSL Research University in Paris found the brain is able to retain what it hears during two types of sleep — rapid eye movement (REM) sleep, and non-REM sleep stage N2. In REM sleep, the last stage in the sleep cycle, sleep and dreaming are more common; in the N2 sleep, a lighter stage of NREM sleep, the brain waves become slower with occasional bursts of rapid waves, and spontaneous periods of muscle tone mixed with periods of muscle relaxation.

Read More: The Sleep-Memory Connection And All The Ways We Can Learn In Our Sleep

When white noise was played during both REM sleep and N2 sleep, participants found it easier to identify the repeated sounds the following day compared to hearing it during deep sleep (stage N3) — when the brain and eyes are active, but the limbs are not. This suggests when information is played during deep sleep, it's harder to learn the information again than if hearing it for the first time. Researchers believe it’s because the brain begins to discard unnecessary memories.

Therefore, the best time to sleep-revise would be during N2 sleep and REM sleep, where we're able to store memories and learn new ones for memory recall when we wake up.

Although brain activity is different during these sleep phases, the brain is able to process complex information, whether it's exogenous information (data from outside sources), during N2 sleep, or endogenous information (data from inside sources), during REM sleep and while dreaming.

According to the press release: "These findings support the idea that N2 and REM sleep favor cerebral plasticity and active memory consolidation, while N3 sleep seems to fulfill the necessary function of unloading memories that would otherwise accumulate day after day."

To assess people's learning ability during sleep, researchers monitored 20 healthy participants during sleep using electroencephalography (EEG), electrooculography (EOG), and electromyography (EMG). Throughout the night, the researchers played white noise, which included several patterns of sound, during wakefulness, rapid eye movement (REM) sleep, and non-REM sleep. The following morning, the participants were tested on their ability to identify patterns they heard during these sleep stages.

REM sleep and N2 sleep led to an increased performance in participants' ability to recognize sounds. However, the researchers were surprised this effect was not seen during deep sleep.

"[W]e saw that participants were worse at detecting the repetitions in the sound that they heard during non-REM sleep, compared to novel items," Thomas Andrillon, study co-author, told The Scientist. He conducted this work as a doctoral student in Sid Kouider’s lab at the Ecole Normale Supérieure de Paris.

Upon analysis of the participants' EEG signals, Andrillon and his team found brain waves could process new information during the lighter stages of non-REM sleep, but this did not occur during the deeper phases of NREM sleep. This suggests learning suppression occurs during this specific stage, which means new information heard during this time may be lost.

It's unclear whether these findings apply to other types of memories, such as learning a new language.

Previous research has found learning a foreign language as you sleep is possible.

In a 2014 study, researchers asked native German speakers to start learning dutch, beginning with some basic vocabulary, and then asked them to go to sleep. While they slept, without prior knowledge, the researchers played the sound of some of the vocabulary words to one group, but not to the other. When the groups were tested, those who listened to them overnight were better able to identify and translate them during NREM or during active or passive waking.

Read More: Sleep Isn't The Only Way To Consolidate New Information

It could be advantageous to know when the brain is most receptive to retaining new information as we sleep. It also suggests we possess the ability to manipulate sleep. However, it's important to thoroughly understand its complexity first and its implications.

Learning is possible during sleep, but it also poses the question of whether it's practical. It's unknown whether this could disrupt our sleep and make us more tied as a result. Sleep is essential to the brain and our physiological functions; not giving our brain a rest could meddle with our day-to-day functioning.

‘While we show that learning is possible during sleep, it could prove quite impractical in our daily lives," said Andrillon.

In a sleep-deprived society, where we're busy and stressed, using sleep to simply sleep could be the best thing we do for our overall health.

Source: Andrillon T, Pressnitzer D, Leger D et al. Formation and suppression of acoustic memories during human sleep. Nature Communications. 2017.

See Also:

Brain Scans Show How Good Sleep Heals The Mind

Getting More Sleep Can Help Improve Memory, Cognitive Function, And Stave Off Alzheimer’s