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Can We Learn While Sleeping? Hypnopaedia: Myth and Reality

Woman sleeping on books


Hypnopaedia (also spelled as hypnopedia) means learning new information while sleeping. The idea of hypnopaedia was largely popular in the 1950s, and since then, companies have sold many audio-cassettes and CDs intended for sleep-learning. It was popular among famous and ordinary people who wanted to improve their image, learn a new language or quit bad habits.

Today we know that sleep plays a vital role in memory and learning, especially memory consolidation (transferring information from short-term memory into long-term memory). However, being exposed to completely new stimuli in sleep hasn’t shown much effect in wakefulness. Learning speeches in sleep seems to be nothing more than a dream that won’t come true. Although some scientists have made progress in the field of hypnopaedia, this progress is extremely limited – it’s mostly linked to sounds and smells.

Where did the idea of hypnopaedia come from?

Probably the first mention of a device used for sleep-learning comes from a science fiction writer Hugo Gernsback and his story written in 1911. Almost two decades later, Alois Saliger invented a device – the Psycho-Phone, claiming that sleep was no different from hypnosis and that we can be equally influenced by suggestions.

After several years, in 1932, Huxley’s Brave New World came out, featuring the idea of hypnopaedia. In the novel, people are instilled moral messages through strings of sentences repeated over and over while they are asleep.

The idea has been deemed impossible by the scientists but became popular once again in the 1950s when EEG (electroencephalograph) was used to track sleep. At about this time, hypnopaedia became a great interest in many fiction books, TV and radio series and films. Perhaps the most famous appearance of the idea is in the novel and film The Clockwork Orange, in which the main character was expected to be rehabilitated – that is, ‘brainwashed’ into a person incapable of crime and violent actions.

Numerous companies have benefited from the popularity of hypnopaedia, selling their audio materials to people from all layers of society.

How does hypnopaedia work?

What is really meant by hypnopaedia is learning by playing a recording while asleep. The idea behind it is that people might be able to learn and actively use the knowledge without any effort. Although an attractive concept, research hasn’t been able to support hypnopaedia in this sense.

However, there has been thought-provoking research telling us humans can learn some very simple pieces of information in sleep.

When new words are played to sleeping people, they will not remember them nor will they be able to recognize that they’ve heard those words in sleep. An interesting study from 2016 presented that words played at night don’t go unnoticed by the brain. Although study subjects were unable to actively recall any of the given words, the EEG recordings uncovered that there was ‘memory trace’ in their neural pathways. This memory trace was not the same for words learned during wakefulness and words presented during sleep. However, this information doesn’t go through the prefrontal cortex, therefore is not retrievable.

Sleep-learning shows results in audio-olfactory (sound-smell) conditioning. A group of people was played a sound, followed by a foul odor during sleep. They were also played a different sound followed by a pleasant smell. In the coming nights, the same sounds were replayed. People learned which sounds match which odors in sleep. After playing the sound associated with a bad smell, people would sniff weakly, as if to avoid the odor – and vice versa; after the other sound, they would sniff strongly. Unlike the first example, where EEG is the only way to see traces of learning, in this study the sniffing behavior persisted in wakefulness. However, subjects were not aware of learning this.

Smells can be used to help people quit smoking – if paired with unpleasant odors while we sleep, cigarette smoke receives an unpleasant association in our minds. This ‘aversive conditioning’ experiment of only one night makes cigarettes off-putting – people wouldn’t smoke for days after. This kind of learning showed the best results when the odor was released during sleep stage 2 (light sleep).

Strengthening memories while sleeping

We have seen that it is possible to learn something new while we sleep, however, apart from the possibility to reduce smoking, how can we practically use this knowledge? We know that our sleep helps consolidate memories, but it seems that memories can be strengthened if certain cues were given during sleep.


Some research suggests that if we are exposed to a certain smell while studying, exposure to the same smell when we sleep will send our brain a memory cue – so we will spend more time of our night’s rest consolidating memories associated with that particular odor. Memory consolidation using olfactory cues was only effective during deep sleep (slow wave sleep), unlike during REM (rapid eye movement) and wakefulness.


An interesting study conducted at Princeton University showed that melodies can be better learned if replayed during sleep. After learning two four-note melodies using a keyboard on a Guitar-Hero-like interface, the subjects took a nap. Only one of the melodies was played during their nap – when they woke up, the subjects were able to play that very melody a lot better than the other one. They also performed significantly better than the group which didn’t get this sound cue.


Even though we cannot actually learn and reproduce new words while sleeping, we can certainly reinforce our vocabulary knowledge by receiving auditory cues (strings of words) during REM sleep (especially when REM follows deep sleep). Deep sleep is important for memory consolidation and is naturally the most present in the first half of the night. So, when we go through deep sleep and then reach REM in which words are played, our success chances for remembering them are the highest. REM sleep is particularly important when it comes to learning languages and individuals with more of this sleep stage perform better in the foreign-language acquisition.

Questions left unanswered – are there any consequences of hypnopaedia?

Sleep is the time for rest. Our brain, free from external distractions like sounds and light, is able to strengthen our memory, replenish neurotransmitters, direct hormone production, and clear out adenosine (a substance which builds up in the brain due to neuron activity – too much of it is linked with Alzheimer’s). Our bodies take a break while tissues and cells are repaired and restored.

This means we need to stop the external activity in order to conduct the maintenance internally. However, with a CD constantly playing in the background, our brains keep picking up information instead of resting. Research shows that even external noise at night such as traffic can increase the risk of cardiovascular diseases and impact the well-being of a person.

Some authors suggest paying special attention to reducing the noise at night. Therefore, we have to ask ourselves whether hypnopaedia impacts the human sleep cycle and to what extent. If we are designed to learn during the day and rest during the night, would introducing new stimuli during sleep impact the period of rest?


Hypnopaedia, as described in science fiction, doesn’t exist. Subliminal language learning from scratch has been proven impossible. However, there are ways in which we can boost our natural memory consolidation primarily through smells and sounds, but only if they are presented in a particular sleep stage. It is still unclear how these cues affect human sleep quality and even overall health if the exposure is prolonged.

Additional Resources

  1. Hume K.I, Brink M, Basner M. Effects of environmental noise on sleep. Health & Sleep. 2012. https://www.ncbi.nlm.nih.gov/pubmed/23257581 Accessed January 15, 2019.
  2. Andrillon T, Kouider S. Implicit memory for words heard during sleep. Oxford Academic. Neuroscience Of Consciousness. January 1, 2016. https://academic.oup.com/nc/article/2016/1/niw014/2757134 Accessed January 15, 2019.
  3. Arzi A, Shedlesky L, et al. Humans can learn new information during sleep. Nature Neuroscience. August 26, 2012. https://www.nature.com/articles/nn.3193 Accessed January 15, 2019.
  4. Rasch B,  Büchel C, et al. Odor Cues During Slow-Wave Sleep Prompt Declarative Memory Consolidation. Science. March 9, 2017. http://science.sciencemag.org/content/315/5817/1426?xid=PS_smithsonian Accessed January 15, 2019.
  5. Antony J. W, Gobel E. W, et al. Cued memory reactivation during sleep influences skill learning. Nature Neuroscience. June 26, 2012. https://www.nature.com/articles/nn.3152 Accessed January 15, 2019.
  6. Batterink L. J,  Westerberg C. E, Paller K. A. Vocabulary learning benefits from REM after slow-wave sleep. Neurobiology of Learning and Memory. July 8, 2017. http://europepmc.org/abstract/med/28697944?xid=PS_smithsonian Accessed January 15, 2019.

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