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We can learn new information when we sleep

Let’s get this out of the way first: no, you cannot play an audiobook under your pillow and wake up as a genius. No, we’re not a step closer to Inception.

That being said, there’s an interesting new study showing that people can learn new information when they sleep. Earlier work tells us that we can certainly strengthen existing memories when we slumber, but actually adding new information is different. And retaining that information when we wake up, even if we have no actual awareness of what we learned, is just plain cool.

I wrote about the new study for The Scientist. Head on over.

Image by Alessandro Zangrilli

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Mutant flies confirm genetic link to restless legs syndrome

In a lab in Atlanta, a group of flies is sleeping fitfully. Their naps are fragmented, and their legs are twitching. Their behaviour is uncannily similar to people who have a condition called restless leg syndrome (RLS). When such people are awake, they experience uncomfortable sensations in their limbs that compel them to move to get some relief. Their sleep, which is fragmented and disturbed, is characterised by the same involuntary movements.

There’s a good reason for these similarities. Amanda Freeman from the Emory University School of Medicine has engineered the flies so that they have a faulty copy of BTBD9, a gene that has been linked to RLS in humans. The fact that they show the same constellation of symptoms strongly suggests that this gene is genuinely involved in the condition.


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Ostriches sleep like platypuses (and look wide awake when they do)

How does an ostrich sleep? Almost imperceptibly, it seems. Even though an ostrich might be sound asleep, it can look wide awake or, at most, a little drowsy. John Lesku from the Max Planck Institute of Ornithology discovered this by fitting six ostrichers with “Neurologgers”, electrode-laden helmets that measures their temperature, brain activity, eye movements and neck muscle contractions.

The video above shows three of the birds cycling through two different types of sleep. The first is called ‘slow wave sleep’ or SWS, where the ostriches’ brain waves are slow and strong. Even though this is typically known as deep sleep, the birds look alert. They stay still, but their eyes are open and their necks upright. Nonetheless, the readings from the Neurologgers clearly showed that they were asleep.

In the second phase, known as ‘rapid eye movement’ or REM sleep, the ostriches’ brain waves are fast and weaker. Now, the birds shut their eyes, which move rapidly behind closed eyelids. They necks also start to droop and sway, righting themselves with awkward jerks like people falling asleep at a talk. Biologists have previously interpreted this as a sign of a tired ostrich. That’s partly right, although the animal is already asleep rather than on its way.


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Genetic snooze button shows that broken sleep impairs memories

Many mental disorders can disrupt the sweet embrace of a long, continuous sleep, including alcoholism, depression, Alzheimer’s and parenthood. And that’s bad news. We know that a good night’s sleep helps to solidify our memories of the previous day’s experiences. And according to a new study, we need a certain amount of continuous sleep for those benefits to kick in.

From an evolutionary point of view, it seems strange that we sleep for hours on end. Rather than leaving ourselves unresponsive and vulnerable for large chunks of time, why not simply sleep over several shorter fragments?

This is not an easy question to answer. Until recently, it has been all but impossible to break up the continuity of sleep without also affecting its quality, or stressing out the animals in question.  But Luis de Lecea from Stanford University has found a way. He has engineered mice with in-built silent alarm clocks. These animals can be woken up at will with a pulse of light delivered directly to their brains.


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To discover the point of sleep, scientists breed flies that nod off on demand

The good news for all new parents is that scientists have found a way of sending individuals straight to sleep by turning up the thermostat. The bad news is that it only works in flies. Alas, this technique is not going to solve anyone’s sleepless nights, but it could tell us something about why we sleep at all.

Every animal, or at least every one with a brain, needs to sleep, but it’s still not entirely clear why. William Dement, who has been studying sleep for six decades, once said, “As far as I know, the only reason we need to sleep that is really, really solid is because we get sleepy.” As Daniel Bushey from the University of Wisconsin writes, “Sleep is perhaps the only major behaviour still in search of a function.”


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Individual neurons go to sleep while rats stay awake

We all know people who look like they can nod off with their eyes open. These exceptions aside, we generally think of sleep as a switch with two settings – you’re either asleep or awake. But Vladyslav Vyazovskiy from the University of Wisconsin-Madison has found that sleep is more complicated than that.

By studying the brains of sleep-deprived rats, Vyazovskiy found that individual neurons can effectively fall asleep, going “offline” while those around them carrying on firing. Even if the rats are awake, parts of their brain can be taking a nap. What we know as “sleep” is the global version of something that happens throughout the brain at a local level.


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Sleepless in Mexico – three cavefish groups independently evolved to lose sleep

Caves are dark, sheltered and often quiet. They’re seemingly ideal places for a bit of a nap. But for a small Mexican fish, they have done exactly the opposite. As a result of life in dark caves, the blind cavefish has evolved sleeplessness, on at least three separate occasions. They don’t go entirely without sleep, but they doze far less than their surface-dwelling relatives.

The blind cavefish (Astyanax mexicanus) is a sightless version of a popular aquarium species, the Mexican tetra. They live in 29 deep caves scattered throughout Mexico, which their sighted ancestors colonised in the middle of the Pleistocene era. In this environment of perpetual darkness, the eyes of these forerunners were of little use and as generations passed, they disappeared entirely. Today, the fish are born with eyes that degenerate as they get older. Eventually, their useless husks are covered by skin.

They went through other changes too. For example, their skin lost its pigment so they are all pinkish-white in colour. And now, Erik Duboué from New York University had found that they also sleep less than their relatives on the surface.


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An injection and a nap: two ways of strengthening memories

The business of encoding new memories is more like writing a document on a computer than inscribing words onto paper. Until you save the file, there’s a chance that you could lose the information. This vulnerable window can last for a couple of days. Only after that point does the memory become strong and long-lasting. This is called ‘consolidation’.

It’s not a permanent state. Whenever we remember something, the fragile window reopens. Again, it’s more like opening a computer document than getting notes out of a drawer. You could easily add, edit or delete information at a flick of a key.  Every time we bring back an old memory, we run the risk of changing it. Again, it takes a while for this window of opportunity to close, for the reactivated memory to strengthen once more. This is called ‘reconsolidation’.

In the last week, two groups of scientists have found two very different ways of boosting both processes, to produce stronger memories.


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To sleep, perchance to dream, perchance to remember

MazeIt seems obvious that thinking about something will help you to remember it better, but it might be more surprising to know that this process works even more efficiently when we’re asleep. Erin Wamsley from Harvard Medical School has shown that people who are trained to navigate a virtual maze learn the best route through it more quickly if they dream about their experiences.

The last decade of research has clearly shown that sleep is one of the best aide memoires that we have. During this nightly time-out, our brain can rehearse information that it has picked up during the day and consolidate them into lasting memories. Wamsley’s new study supports that idea but it also shows that dreaming while you nap can strengthen our memories even further.

Maze_taskShe asked 99 volunteers to learn the layout of a complex virtual maze so that they could reach a specific landmark after being dropped at a random starting point. Five hours later, they were tested again. Those who had stayed awake in the intervening time beat their previous times by 26 seconds, but those who had had a 90-minute nap improved by a whopping 188 seconds.

But those who dreamt about the task fared even better. Wamsley either asked her recruits directly about whether they dreamt about the labyrinth, or asked them to give an open-ended report of everything that was going through their mind while they were asleep. Either way, those who had thought about the maze during their short nap improved far more than those who didn’t. They also beat those who mentally replayed their training again while awake. These striking results suggest that there’s something special about the mental rehearsals that happen during dreaming sleep.


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Memories can be strengthened while we sleep by providing the right triggers

In my final year of university, with exam deadlines looming and time increasingly fleeting, I considered recording some of my notes and playing them over while I was asleep. The concept of effectively gaining 6 extra hours of revision was appealing, but the idea didn’t stick – it took too long to record the information and the noise stopped me from sleeping in the first place. And the whole thing had a vague hint of daftness about it. But a new experiment suggests that the idea actually has some merit, showing that you can indeed strengthen individual memories by reactivating them as you snooze.

Sleep is a boon to newborn memories. Several experiments have shown that sleep can act as a mental cement that consolidates fragile memories into stable ones. But John Rudoy from Northwestern University wanted to see if this process could be taken even further by replaying newly learned information while people slept.

He asked a dozen volunteers to remember the positions of 50 different objects as they appeared on a screen. The items, from kittens to kettles, were all accompanied by a relevant noise, like a meow or a whistle. Shortly after, the recruits all had a short nap. As they slept, Rudoy played them the sounds for 25 of the objects, against a background of white noise. When the volunteers woke up, they had to place each of the 50 objects in the right position, and they were marked on how close they came to the actual target.

The results were very clear – the volunteers positioned the objects around 15% more accurately if they’d heard the relevant sounds while they slept. Although the sleep sounds didn’t work for everyone, the majority of the participants – 10 out of 12 – benefited in some way. And none of them knew they heard anything at all while they slept. When they were told this and asked to guess which sounds they heard, they didn’t do any better than chance.  


To show that this isn’t just a general benefit of revision, whether conscious or not, Rudoy did a similar experiment. This time, his volunteers heard the noises after they had first seen the objects but while they were still awake. This group proved to be no better at remembering the items’ locations than those who didn’t hear the second round of sounds.

Finally, to understand what was going on in the brains of the slumbering recruits, Rudoy used electroencephalograms (EEG) to measure the electrical activity in the heads of 12 fresh volunteers. He showed that people who were better at remembering the objects’ positions after their nap were also those who showed the most brain activity when they heard the sounds Rudoy thinks that hearing the sounds during sleep prompted the brain to rehearse and strengthen associations between the objects and their locations.

Some people think that sleep improves memories in a general way, by making our brains more flexible and easing the incorporation of new information. But these simple experiments show that the benefits can be very specific indeed. It’s not only possible to strengthen specific and individual memories by providing the right triggers, but we get the opportunity to do so every single night.

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Even without practice, sleep improves memory of movements

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

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Sleeping on it – how REM sleep boosts creative problem-solving

Blogging on Peer-Reviewed ResearchThe 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.


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The point of sleep, or, Do fruit flies dream of six-legged sheep?


Blogging on Peer-Reviewed Research
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).


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Portable brain activity-recorder shows that sloths aren’t all that sleepy

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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.  

Sleeping-Sloth.jpgA 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.