Can you learn in your sleep?

Just before you climb under your duvet, you carefully prepare your room. You sprinkle a few drops of incense on your pillow, put on some headphones, and place a strange-looking band over your scalp. Then you go to sleep. The ritual takes just a few minutes, but you hope this could accelerate your learning of a diverse range of skills: whether you are trying to master the piano, tennis or fluent French. You won’t recall a single aspect of the night’s “training” – but that doesn’t matter: your performance the next morning should be better, all the same.

The idea of learning as you sleep was once thought very unlikely, but there are several ways – both low- and hi-tech – to try to help you acquire new skills as you doze. While there is no method that will allow you to acquire a skill completely from scratch while you are unconscious, that doesn’t mean that you still can’t use sleep to boost your memory. During the night, our brain busily processes and consolidates our recollections from the day before, and there could be ways to enhance that process.

Given that we spend a third of our lives in the land of nod, it is little wonder that sleep learning has long captured the imagination of artists and writers. In most incarnations, it involved the unconscious mind absorbing new information from a recording playing in the background. In Aldous Huxley’s Brave New World, for instance, a Polish boy learns English after having slept through a radio lecture by George Bernard Shaw; the authoritarian government soon uses the same technique to brainwash its subjects. More recently, in The Simpsons, Homer buys a tape to subliminally reduce his appetite as he sleeps, only to find that it is instead changing his vocabulary. When his wife, Marge, asks if his diet is working, the normally inarticulate Homer replies: “Lamentably, no. My gastronomic rapacity knows no satiety”.

Bad science

In reality, this particular kind of sleep learning is almost certainly impossible. Although some early studies suggested that subjects could pick up some facts as they slept, the researchers couldn’t be sure that they hadn’t just awoken to listen to the recording. To test those suspicions, Charles Simon and William Emmons attached electrodes on the scalps of their subjects, allowing them to be sure that they only played the tapes once the subjects were dozing. As they had suspected, the subjects learnt nothing once they had dropped off. The results were published in the 1950s, but entrepreneurs over the years have still tried to cash-in on the attraction of effortless learning with various products – even though their methods had no scientific basis.

Monitoring brain activity of sleeping people suggests they can't learn new skills while unconscious (SPL)

Despite being blind and deaf to new information, however, the sleeping brain is far from idle: it mulls over the day’s experiences, sending memories from the hippocampus – where memories are first thought to form – to regions across the cortex, where they are held in long-term storage. “It helps stabilise the memories and integrate them into a network of long-term memory,” says Susanne Diekelmann at the University of Tubingen in Germany. Sleep also helps us to generalise what we’ve learnt, giving us the flexibility to apply the skills to new situations. So although you can’t soak up new material, you might instead be able to cement the facts or skills learned throughout the day.

Smell enhancer

So far, at least four methods have shown promise. The simplest strategy harks back to the research of a 19th Century French nobleman named the Marquis d’Hervey de Saint-Denys. As he explored ways to direct his dreams, the Marquis found that he could bring back certain memories with the relevant smells, tastes or sounds. In one experiment, he painted a scantily clad woman while chewing an orris root; when his servant then placed the root in his mouth as he slept, the tart flavour brought back visions of the same beautiful lady in the foyer of a theatre. She was wearing “a costume that would have hardly been acceptable to the theatre committee”, he wrote with delight in his book, Dreams and How to Guide Them. Another time, he asked the conductor of an orchestra to play certain waltzes whenever he danced with two particularly attractive women. He then rigged up a clock to a music box, so that it played the same tunes during the night, which apparently brought their handsome figures to his sleeping mind.

The Marquis simply wanted to seed his slumbers with pleasant (and sometimes lustful) experiences, but it now looks like the same approach can also trigger the sleeping brain to replay the learning of skills or facts, reinforcing the memory in the process.