When we think of memory aids, we consider repeating what we’ve learned, using clever mnemonics, or breaking information down into bite-size chunks. But one of the best memory aids we have available to us is something we all do on a daily basis – sleep. Studies have found that sleep enhances our memories of facts and physical skills alike. It can even help us remember movements that we see others do.
But this only works within a short window. Ysbrand van der Werf from the Netherlands Institute of Neuroscience found that people who saw a video of someone tapping keys on a laptop remembered the sequence more accurately if they slept on it within 12 hours. Any longer than that, and the snoozing didn’t boost their recall.
Van der Werf showed the video to 128 volunteers and then tested them on either the same finger-tapping sequence or a different one. The gap between video and test was either 12 or 24 hours, and some of the volunteers were allowed to sleep during the interval while others were not.
If the test sequence didn’t match the ones they saw, all the recruits did equally well. But if the sequence was the same, those who managed to sleep within the first 12 hours stood out – they were 22% faster and made 42% fewer errors than their peers who either didn’t sleep or who slept later. They even improved whether they had their naps during the day or in the evening.
These results parallel those from experiments where people actually had a chance to practice new skills before their naps. The big difference here is that the improvements came only after watching movements rather than actually performing them.
Van der Werf confirmed that by taking great care to ensure that his volunteers weren’t actually trying out the keystrokes for themselves. While watching the video, they had to tap two different keys to keep their fingers busy. Van der Werf even measured the muscle activity in the arms of seven volunteers to rule out the possibility that they were making subtle, unnoticed finger movements.
If it’s not to do with practice, it’s not to do with memorising the digits themselves or the position of the keys either. If the volunteers just saw the numbers flash up on screen, or if they saw coloured squares light up in the same position as the relevant keys, they didn’t become more accurate or faster when they had to replicate the sequence. They needed to actually see someone else doing it.
Van der Werf thinks that the recruits probably imagined their finger movements while watching the video, even if they didn’t actually try them out. It may even involve the mirror neurons that fire when an individual performs an action and when it sees someone else doing the same action (although mirror neurons have only been properly found in monkeys, and not humans).
Either way, the results highlight the importance of a good sleep when people are trying to pick up new physical skills. This could be especially important for people who can’t possibly to practice the movements in question, such as those who have suffered a stroke or broken a limb. And clearly the most important implication is that the next time I see someone doing parkour, I will immediately lie down and have a little nap. When I wake up, I will be Batman. SCIENCE!
Reference: PNAS doi:10.1073_pnas.0901320106
More on memory:
The German chemist Friedrich Kekule claimed to have intuited the chemical structure of the benzene ring after falling asleep in his chair and dreaming of an ouroboros (a serpent biting its own tail). He’s certainly not the only person to have discovered a flash insight after waking from a good sleep. In science alone, many breakthroughs were apparently borne of a decent snooze, including Mendeleyev’s creation of the Periodic Table and Loewi’s experiments on the transmission of nervous signals through chemical messengers.
Most of us have tried sleeping on a difficult problem before and using an elegant experiment, Denise Cai from the University of California in San Diego has shown that this old technique really does have merit to it. She found that our brains are better at integrating disparate pieces of information after a short bout of REM (rapid eye movement) sleep – a deep, dream-rich slumber that involves a rapid fluttering of the eyes. Cai thinks that REM sleep catalyses the creative process by allowing the brain to form connections between unrelated ideas.
Cai is by no means the first person to link sleep or dreaming to creative revelations, but she is one of the few to test it directly through experiments. She asked 77 people to complete a task, where they were given a list of three words and had to find a fourth that was linked to all three. For example, ‘cookie’, ‘heart’ and ‘sixteen’ are all associated with ‘sweet’. In each example of this ‘Remote Associates Test‘ (RAT), the missing fourth word has a different relationship to each of the three targets.
Feeling exhausted after a long day is an all too familiar part of modern life. We drag ourselves into bed, hoping to shut down our minds for a night, waking up recharged the next day. But contrary to popular belief, your brain does anything but shut down during sleep.
Science is beginning to reveal that sleep is a crucial chance for the brain to consolidate the massive amount of sensory information it receives during the day. It acts as a time-out between periods of consciousness and gives the brain a chance to weave lasting memories from experiences.
For something that is so crucial to our survival, the purpose of sleep is still an enigma to science. It is not simply a question of conserving energy – after all, continually eating doesn’t make you feel any more rested. Now, Indrani Ganguly-Fitzgerald and colleagues from the Neurosciences Institute, San Diego, are drawing back the curtain on the function of sleep. And they are doing it by studying that animal so favoured of geneticists, the fruit fly, Drosophila melanogaster (below).
Three-toed sloths have a reputation for being some of the sleepiest of all animals, largely due to a single study, which found that captive sloths snooze for 16 hours a day. That certainly seems like a sweet deal to me, but it seems that the sloth’s somnolent reputation has been exaggerated.
A new study – the first ever to record brain activity in a wild sleeping animal – reveals that wild sloths are far less lethargic than their captive cousins. In their natural habitat, three-toed sloths sleep for only 9.6 hours a day, not much more than an average first-year university student.