Sleep learning used to be a pipe dream. Now neuroscientists say they have found ways to enhance your memory with your eyes closed, says David Robson. 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 strangelooking 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. 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 longterm 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. 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. In the near future, technology may offer further ways of upgrading the brain’s sleep cycles. Memory consolidation is thought to occur during specific, slow, oscillations of electrical activity. So the idea here is to subtly encourage those brain waves without waking the subject. Jan Born, at the University of Tubingen, has been at the forefront of these experiments. In 2004, he found that he could help amplify those signals using transcranial direct current stimulation (tDCS), which passes a small electric current across the skull, successfully improving his subjects’ performance on a verbal memory test. More recently, he has turned to an even lessinvasive form of stimulation, which uses a skullcap of electrodes to measure neural activity, while headphones deliver sounds that are in sync with the brain waves. “You deepen the slow wave sleep and make it more intense,” says Born. “It’s a more natural way of getting the system into a rhythm,” he says.
If the idea of going to sleep with a cumbersome headset doesn’t appeal, Miriam Reiner at the Technion Institute of Technology in Haifa, Israel may have a more attractive solution. She hopes to use a form of neurofeedback, which allows subjects to control their neural activity while awake. In her setup, an electrode attached to the subject’s head feeds into a simple computer game, in which the subject is advised to drive a car with the power of their thoughts. When the electrode records the right frequency of brainwaves, normally associated with memory consolidation during sleep, they accelerate; when they don’t, it slows down. The idea is to kick-start memory consolidation straight after learning. It gives the sleeping brain a head-start as it sets about reorganising the day’s events. Needless to say, we will need to see bigger trials with many more subjects before these techniques should be recommended for everyday use. Since the experiments have so far used somewhat artificial tests of learning and memory, it would also be useful to see how they fare on more useful tasks; Reiner is beginning to take a few steps in this direction by testing whether her neurofeedback can help students learn the guitar. Diekelmann also thinks that we need to confirm that these memory hacks don’t have unexpected consequences. “If you enhance one set of memories, maybe you’d impair another set,” she says.