In Aldous Huxley’s 1932 novel Brave New World, a Polish boy, Reuben Rabinovitch, falls asleep next to a radio receiver. When he wakes up, he is able to recite the entire broadcast. He has no idea what any of it means, though – it’s all in English.

Countless articles today claim that you can actually learn music, hone your foreign language skills, or cram for tomorrow’s maths exam during sleep. And there is a whole industry trading on this idea. Subliminal message tapes, popularised by the self-help guru Tony Robbins, promise to help you stop smoking, lose weight, and even brush up your golf skills and find love – all the while catching some shut eye.

The big sell of “sleep learning” is seductive – how lovely it would be to be productive while we lie like lifeless lumps in bed. But is it actually based on any evidence?

What the research says

The idea that you can learn facts and figures while listening to a recording in a “hypnotic state”, like sleep, was debunked in a simple 1950s experiment. Researchers Charles Simon and William Emmons attached electrodes to the scalps of participants to observe them as they went in and out of sleep states. While they slept, Simon and Emmons played a tape of a person listing 96 facts about history, science, sports, and other topics. The subjects were asked trivia questions after awakening, but there was no evidence that they’d retained any of the information that was played to them. The researchers concluded that sleep-learning was “impractical, and probably impossible”.

More recent research has tied in Ivan Pavlov’s notion of classical conditioning – the idea that we respond to new information when it’s paired with a stimulus that elicits an innate response. In 2010, Susan Diekelmann and colleagues in Germany published a study in which subjects examined specific patterns of objects on a grid before sleeping in the laboratory. While studying, each subject was exposed to a subtle odour in the room, which was later re-introduced when subjects were in a sleep stage called slow-wave sleep. Subjects remembered 84% of the objects’ locations when their memories were paired with the odour during sleep.

Then a 2012 study by a US group reported that participants were more likely to correctly play a melody in a musical video game (similar to Guitar Hero) if the tune had been previously played to them during the slow-wave stage of a 90-minute nap. The authors suggested that learning can occur subconsciously during sleep.

Learning while you sleep, or learning because you sleep?

A study published last year by Swiss researchers suggested that sleep enhances our ability to learn foreign language words. Subjects were presented with a series of Dutch-to-German word pairs at 10 pm, then listened to an audio recording of these word pairs until 2 am. Half of the group, however, was allowed to sleep during this period. When re-assessed, the researchers found that those who slept recalled significantly more words than those who didn’t.

Learning a new language while you sleep makes the story of Huxley’s Polish boy seem almost possible. But are the subjects actually learning from the audio recordings during their sleep? Or, rather, are their memories improved simply because they slept?

In fact, slow-wave or deep sleep has been recognised for some time as critical for memory consolidation – the stabilisation of memory from short-term to long-term. During slow-wave sleep, which tends to happen during the first half of the night, the firing of our brain cells is highly synchronised. When we measure sleep using electrodes attached to the scalp, slow-wave sleep appears as slow, high-amplitude oscillations.

These “slow waves” originate in the neocortex and make a circuit with the hippocampus, the brain structure which encodes new memories. Scientists believe that this connection allows for newly-learned information to be repeatedly activated with each oscillation. It’s been shown that patients with insomnia, who experience less slow-wave sleep than normal sleepers, show impaired memory consolidation.

Your best bet? Let sleeping dogs lie

So, yes, we can learn during sleep – a bit. However this is mostly limited to making subconscious associations, like pairing scents with images. This is not exactly practical in the real world, nor will it likely lead to long-term memory storage.

For more complex learning, such as baseball statistics or foreign language vocabulary, it’s more likely that sleep is helping to consolidate what we’ve already learned, not actively processing new incoming signals.

Instead of donning clunky headphones or spritzing your pillow with the same lavender scent you used while studying for your Spanish test, it’s probably best to stop trying to “hack” your sleep. Our brains have developed a pretty clever mechanism for helping us learn new information. Be kind to your noggin and give yourself enough sleep to take advantage of it.

Get involved with the Use your head series by joining the discussion on #useyourhead or pitching your ideas to natalie.gil.casual@theguardian.com

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