During deep sleep, cerebrum cleans what it doesn’t need, study finds
During deep sleep, the brain may be tidying up the detritus that accumulates during a hard day of thinking, a recent study suggests.
Researchers have found that during slow-wave sleep in particular – the type of slumber sandwiched between periods of dreaming – a sort of cleaning fluid pulses into the brain, taking out the trash as it recedes, according to a report published in Science.
Using high-speed brain imaging, the researchers were able to map out a series of events that occur as the brain enters deep sleep and brain waves start to slow and synchronize.
They found that the blood flow to the brain diminishes, allowing for an influx of clear, colourless cerebrospinal fluid (CSF). That fluid surges in and sloshes around, washing away the day’s detritus of proteins and other waste substances that might harm the brain if they aren’t cleared out.
“We haven’t ever seen CSF waves on this scale in the awake brain, suggesting that sleep involves a unique pattern of fluid flow in the brain,” said Laura Lewis, an assistant professor of biomedical engineering at Boston University and the study’s senior author.
“Previous studies in animals from other labs have shown that during sleep, proteins such as beta-amyloid (one of two hallmark proteins implicated in Alzheimer’s disease) are cleared more rapidly from the brain,” Lewis said. “Based on these studies; we wondered why this might occur and we wanted to ask whether CSF changes during sleep because CSF is thought to be important for waste removal.”
Lewis and her colleagues suspect that poor sleep in patients with neurological disorders might impact the tidying up process, leaving waste materials to accumulate, eventually leading to degeneration.
“We’re running new studies to test how these CSF waves may change in healthy aging and in neurological disorders,” she said. “We’re also going to test whether this would be associated with less waste removal from the brain during sleep in these patients.”
The new research shows how the rhythmic flow of fluid during deep sleep could be the way the brain washes away waste, Danish researchers write in a commentary that accompanied the new study.
Understanding that process might shed a light on how disturbed sleep could be linked to certain neurologic disorders, write Soren Grubb, an assistant professor in the department of neuroscience at the University of Copenhagen, and Martin Lauritzen, a professor of clinical neurophysiology at Rigshospitalet.
“Disturbances of (slow wave sleep) commonly accompany aging, major depressive disorders and dementia,” they note.
“It will be interesting to assess whether the CSF dynamics linked to SWS can be used as a biomarker for disease states and whether strategies to restore SWS can rescue brain function in neurodegeneration.”
We can now amplify the restorative benefits of sleep. Could this help us cope with later nights and early mornings?
We often wear our sleeplessness as a badge of pride – a measure of our impossibly hectic schedules. Thomas Edison, Margaret Thatcher, Martha Stewart and Donald Trump have all famously claimed to get by on just four or five hours’ sleep a night – much less than the seven-to-nine hours recommended to most adults. Many of us are following suit: according to the Centers for Disease Control and Prevention, more than one third of US adults fail to get enough sleep on a regular basis.
The consequences – including impaired memory and decision making, and increased risk of infection and obesity – are well known, but easy to ignore. When our immediate demands exceed the hours in the day, sleep is still our top sacrifice.
But what if we were able to simply optimise the sleep experience so that we enjoyed most of the benefits of deep sleep, in less time?
This possibility may be closer than it sounds, thanks to new ‘sleep optimisation’ techniques. Various experiments across the world have shown that it is possible to boost the efficiency of the brain’s night-time activity – speeding up the descent into deep sleep and enhancing our rest once we get there.
It sounds almost too good to be true. Is it?
A slower beat
On a regular night, the brain cycles through many different stages of sleep, each with a characteristic pattern of ‘brain waves’, in which neurons in different regions of the brain fire together, in synchrony, at a particular rhythm. (It’s a bit like a crowd chanting or beating a drum in unison).
It is notoriously hard to convince sleep-deprived people to make the necessary lifestyle changes
During the rapid eye movement (REM) phases that rhythm is fairly fast – during which time we are most likely to dream. But at certain points our eyes cease to move, our dreams fade and the rhythm of the brain waves drops to less than one ‘beat’ a second – at which point we enter our deepest, most unresponsive state of unconsciousness called ‘slow-wave sleep’.
It is this stage that has been of particular interest to scientists investigating the possibility of sleep optimisation.
Research since the 1980s has shown that slow-wave sleep is essential for the brain’s maintenance. It allows the necessary brain regions to pass our memories from short-term to long-term storage – so that we don’t forget what we have learnt. “The slow waves facilitate the transmission of information,” says Jan Born, director of the Department of Medical Psychology and Behavioural Neurobiology at the University of Tübingen, Germany.
The slow waves may also trigger the flow of blood and cerebrospinal fluid through the brain, flushing out potentially harmful debris that could cause neural damage. They also lead to dips in the stress hormone cortisol and help to rejuvenate the immune system so that it is readier to fight incoming infections.
Such results led scientists including Born to wonder whether we might therefore be able to enhance the benefits of sleep and improve our daytime functioning by boosting the production of those slow waves.
One of the most promising techniques to do so works a bit like a metronome counting the brain into the correct rhythms. Experimental participants wear a headset that records their brain activity and notes when they have started to make those slow waves. The device then plays short pulses of gentle sound, beginning in sync with the brain’s natural slow waves, at regular intervals over the night. The sounds are quiet enough to avoid waking the participant, but loud enough to be registered, unconsciously, by the brain.
Born has led much of the experimental work, finding that this gentle auditory stimulation is just enough to reinforce the right brain rhythms, deepening the slow-wave sleep compared with people receiving sham stimulation. Participants wearing the headset performed better on memory tests, showing increased recall for material they had learnt the day before. It also altered their hormonal balance – reducing their cortisol levels – and led to an improved immune response.
In the trials to date, participants haven’t yet reported unwanted responses to the technique. “We can’t really be sure, but so far there are no obvious side effects,” says Born.
Better sleep, in a store near you
Most of the studies attempting to boost slow-wave sleep have been conducted on small groups of young, healthy participants, so to be certain of the benefits of boosting slow-wave sleep, we would need to see larger trials on more diverse groups. But based on the existing evidence, the technology has already made its way into a handful of consumer devices, mostly in the form of headbands to be worn overnight.
The French start-up Dreem, for instance, has produced a headband (available for around €400 or £330) that also uses auditory stimulation to boost slow-wave sleep using a similar set-up to the scientific experiments – effects have been confirmed in a peer-reviewed trial. The Dreem device also connects to an app that analyses your sleep patternsand offers practical advice and exercises to help you get a better night’s rest. These include things such as meditation and breathing exercises that might ensure you get to sleep quicker and with fewer awakenings during the night. The aim is to improve overall sleep quality across the night for anyone who feels that they could do with a deeper rest.
Philips’s SmartSleep Deep Sleep Headband, in contrast, is very explicitly aimed at making up for some of the ill-effects of sleep deprivation – for people “who, for whatever reason, are simply not giving themselves an adequate sleep opportunity”, says David White, Philips’ chief scientific officer.
The device was first launched in 2018, and like Dreem’s product, it is a headband that senses the brain’s electrical activity and periodically plays short bursts of sound to stimulate the slow oscillations that are characteristic of deep sleep. It relies on smart software that carefully adapts the volume of its sound over time to ensure that it delivers the optimum level of stimulation for the specific user. (The device is currently only available in the US for $399.)
White agrees that the device cannot fully replace a full night’s sleep, but he says that it is notoriously hard to convince sleep-deprived people to make the necessary lifestyle changes. By amplifying the benefits of the sleep they do manage to get, this device should at least help them to function better in daily life. Along these lines, Philips’s own experiments have reportedly confirmed that the SmartSleep boosts slow-wave sleep in sleep-deprived people, and that it mitigates some of the immediate effects like poorer memory consolidation.
Future research may suggest many more innovative ways to optimise our sleep. Aurore Perrault at Concordia University in Montréal has recently tested a gently rocking bed that swayed back and forth every four seconds.
Participants were quicker to enter slow-wave sleep, and spent more time in that crucial sleep cycle, as the brain waves synchronised with the external movement
She says that the technique was inspired by a colleague’s new-born baby being rocked to sleep, leading the team to wonder whether adults may also benefit from gentle movement. Sure enough, they found that the participants were quicker to enter slow-wave sleep, and spent more time in that crucial sleep cycle, as the brain waves synchronised with the external movement. As you might hope, they also reported feeling more relaxed at the end of the night, and this was again accompanied by the expected knock-on benefits for their memory and learning. “That was the cherry on the top,” says Perrault.
If such a bed were brought to market it could serve a similar purpose to the sound-stimulating headbands. Perrault is particularly interested whether it might help older people. The amount of time we spend in short-wave sleep seems to decline as we age, potentially contributing to some age-related memory problems – and she hopes that gently swaying beds may be one way to counteract that.
Still, get some sleep
Although the field is still in its infancy, these studies show that there is a lot of promise in the general concept of sleep optimisation to increase the power of our slumbers (however much or little we get).
Perrault and Born are both optimistic about the potential of the commercial products using pulses of sound to stimulate those regenerative slow waves. Perrault emphasises that we still need larger studies to ensure their effectiveness outside the carefully controlled conditions of the lab – but she welcomes that this research could now benefit a wider population.
“It’s great that they’re trying, more and more, to use external stimulation because we know that it impacts sleep,” says Perrault.
In the future, it will be interesting to see whether sleep optimisation could also bring benefits in the long term. We know that chronic sleep loss can increase the risk of conditions like diabetes and even Alzheimer’s disease – but it’s by no means clear that these new techniques will help reduce those risks.
For now the only guaranteed way of reaping all the benefits of sleep – both long and short-term – is to make sure you get enough of it. Whether or not you decide to give these devices a try, you should attempt to schedule more early nights, and avoid too much alcohol, caffeine and screen time before bed – factors that are all known to damage the quality of our sleep.
Our brains cannot function without a recharge – and anyone hoping to live a happy, healthy, productive life needs to wake up to that fact.
Sleep is a normal and indeed essential part of our lives. But if you think about it, it is such an odd thing to do. At the end of each day we become unconscious and paralysed. Sleep made our ancestors vulnerable to attack from wild animals. So the potential risks of this process, which is universal among mammals and many other groups, must offer some sort of evolutionary advantage. Research in this area was slow to take off. But recently there has been a series of intriguing results that are giving researchers a new insight into why we sleep and what happens when we do it.
Why do I sleep?
Scientists simply don’t know for sure. In broad terms researchers believe it is to enable our bodies and especially our brains to recover. Recently researchers have been able to find out some of the detailed processes involved. During the day brain cells build connections with other parts of the brain as a result of new experiences. During sleep it seems that important connections are strengthened and unimportant ones are pruned. Experiments with sleep-deprived rats have shown that this process of strengthening and pruning happens mostly while they sleep. And sleep is also an opportunity for the brain to be cleared of waste. A group led by Prof Maiken Nedergaard at the University of Rochester Medical Centre in New York discovered a network of microscopic fluid-filled channels in rats that clears waste chemicals from the brain. Prof Nedergaard told us when her research was first published in 2013 that this process occurs mostly when the brain is shut off. “You can think of it like having a house party. You can either entertain the guests or clean up the house, but you can’t really do both at the same time.”
What happens when I don’t get enough sleep?
It seems that a lack of sleep alters the way in which the genes in the body’s cells behave. Researchers at Surrey University in Guildford have found that genes involved in inflammation seem to increase their activity. Dr Malcolm von Schantz, who is involved with the Surrey research, believes that the genes are responding to lack of sleep as if the body is under stress. He speculates that in the distant past in times of stress our ancestors’ bodies would prepare themselves for injury by activating these inflammation genes which would cushion the effects of attacks by wild animals or human enemies. “It puts the body on alert for a wound but no wound happens,” he told Sleep Advice. “This could easily help explain the links between sleep deprivation and negative health outcomes such as heart disease and stroke.” In modern times though preparing for an injury that never happens has no beneficial effect – in fact the consequent activation of the immune system might increase the risk of heart disease and stroke.
Why is it hard to think when I am tired?
The expression “half asleep” might be an accurate description of what is going on in the brain when you are feeling slow-witted. Research suggests that parts of the human brain may well be asleep when it is sleep-deprived. Studies on whales and dolphins show that when asleep they continue to use half of their brain to swim and come up to the surface for air. A study on human patients showed that something similar goes on in our brains. As they became more sleep-deprived, parts of their brain became inactive while they were still awake. What’s more the local sleep areas move around the brain. So although when we go to bed we think one moment we are awake and then there is an abrupt change to sleep – it may well be more of a continuous process.
What is the role of dreaming?
That’s a question that psychiatrists, notably Carl Jung and Sigmund Freud, have tried to answer but with limited success. More recently a team at the ATR Computational Neuroscience Laboratories in Kyoto in Japan has begun trying to answer some of these questions by building the beginnings of a dream-reading machine. They asked volunteers to doze off in an MRI scanner and recorded their brain patterns. The volunteers were then woken up and asked to tell researchers what they were dreaming about. The team then listed 20 separate categories of dream content from these accounts such as dwelling, street, male, female, building or computer screen. The researchers then compared the accounts with the pattern of activity in the area of the brain responsible for processing visual information – and to their amazement they found that there was a correlation. So much so that they could predict which of the 20 different categories they had listed the patient had dreamt of with 80% accuracy. The device is a very rough tool but it may well be a first step to something that can see in more detail what happens in our dreams and so help researchers learn more about why we dream.
How is modern life affecting our sleep patterns?
Several studies show that the light bulb has led people shifting their day and getting less sleep. On average we go to bed and wake up two hours later than a generation ago. The US Centres for Disease Control reported in 2008 that around a third of working adults in the US get less than six hours sleep a night, which is 10 times more than it was 50 years ago. In a later study it was also reported that nearly half of all the country’s shift workers were getting less than six hours sleep. And a study led by Prof Charles Czeisler of Harvard Medical School found that those who read electronic books before they went to bed took longer to get to sleep, had reduced levels of melatonin (the hormone that regulates the body’s internal body clock) and were less alert in the morning. At the time of publication he said: “In the past 50 years, there has been a decline in average sleep duration and quality. “Since more people are choosing electronic devices for reading, communication and entertainment, particularly children and adolescents who already experience significant sleep loss, epidemiological research evaluating the long-term consequences of these devices on health and safety is urgently needed.”
What’s stopping you sleeping?
– One in eight of us keep our mobile phones switched on in our bedroom at night, increasing the risk our sleep will be disturbed.
– Foods such as bacon, cheese, nuts and red wine, can also keep us awake at night.
Many studies report that there is evidence that sleep loss is associated with obesity, diabetes, depression and lower life expectancy – while others, such as Prof James Horne, a sleep researcher at Loughborough University believes that such talk amounts to “scaremongering”. “Despite being ‘statistically significant’, the actual changes are probably too small to be of real clinical interest,” he told Sleep Advice. “Most healthy adults sleep fewer than that notional ‘eight hours’ and the same went for our grandparents. “Our average sleep has fallen by less than 10 minutes over the last 50 years. Any obesity and its health consequences attributable to short sleep are only seen in those few people sleeping around five hours, where weight gain is small – around 1.5kg per year – which is more easily rectified by a better diet and 15 minutes of daily brisk walking, rather than by an hour or so of extra daily sleep.” A team from the universities of Surrey and Sao Paulo in Brazil have spent the past 10 years tracking the health of the inhabitants of Bapendi, a small town in Brazil where modern day lifestyles haven’t yet taken hold. Many of the inhabitants of this town get up and go to bed early. The investigators hope to find out soon whether the old adage “early to bed and early to rise” really does make us, if not “wealthy and wise”, at least “healthy and wise”.
We might feel drowsy as we start to fall asleep, but our brain is still active, and noises or discomfort can disturb us. As we drift into light sleep, an area of the brain called the hypothalamus starts to block the flow of information from our senses to the rest of the brain. But it will still let through noises, which need to be able to wake us up. After about half an hour of light sleep, most of us enter a type of deep sleep called slow-wave sleep. Our brains become less responsive and it becomes much harder to be woken up. But some things will always get through – such as our names being called out loudly. Missing out on parts of our usual sleep cycle reduces the quality and quantity of sleep.
We all have a built-in body clock which tells us when we are tired. It helps synchronise thousands of cells in our body to a 24-hour cycle called the circadian rhythm. The main synchroniser for our body clock is light. Our eyes react to light and dark, even when our eyelids are closed. Daylight prompts our brains to reduce the production of the sleep hormone melatonin. This makes us feel more alert. If we get less sleep during the night, because of going to bed late or waking up early, we’re unlikely to get as much deep sleep as we need.
The wrong temperature
Our core body temperature should drop by half a degree when we are asleep. So as sleep approaches, our body clock makes blood vessels in our hands, face and feet open up, in order to lose heat. But if we get too cold, we get restless and find it hard to sleep. Or if our bedrooms or duvets are too warm, our bodies can’t lose heat, which can also cause restlessness.
Stimulating food and drink
We can have trouble sleeping after we consume food and drink that act as stimulants.
Drinks high in caffeine make it harder to fall asleep and can interfere with our deep sleep. Caffeine can stay in our system for many hours, so our sleep quality can be affected by the caffeinated drinks we consume earlier in the day.
In the course of a night we usually have six to seven cycles of REM (rapid eye movement) sleep, during which our brains process the information we’ve absorbed during the day. This leaves us feeling refreshed. But a night of drinking means we’ll typically have only one to two cycles and wake up feeling tired.
Foods containing a chemical called tyramine, such as bacon, cheese, nuts and red wine, can keep us awake at night. This is because tyramine triggers the release of noradrenaline, a brain stimulant.
A busy mind
Stress is the enemy of sleep. In bed, our mind is left free to wander and anxiety concerning sleep will only make it worse. It’s difficult to keep track of time when you’re lying down in the dark waiting for sleep. People often nod off and wake up again but it feel as if they’re getting no sleep at all. This delivers fragmented sleep with much less time spent in the important deep sleep stages.
Sleep experts recommend that people with this problem get up and do an activity which distracts the mind from worry – such as a puzzle – before trying to sleep again.
Do you like to have a weekend lie-in or a nightcap before going to bed? These habits could actually be harming your sleep.
Relax your mind
Simple breathing exercises can help. Breathe, using your abdomen not your chest, through your nose for three seconds, then breathe out for three seconds. Pause for three seconds before breathing in again. Practise this for ten minutes at night (five minutes is better than nothing).
Some people find that lavender oil, valerian or other herbs help them to sleep.
If you still have problems, you could try massage, aromatherapy, or even acupuncture.
If you still find yourself tossing and turning, abandon the bedroom and find something enjoyable and absorbing to do. Jigsaws are perfect. Don’t go back to bed until you begin to feel sleepy.
Regular exercise is a great way to improve your sleep. Just be careful not to do it close to bed time as exercise produces stimulants that stop the brain from relaxing quickly.
This being the case, exercising in the morning is an excellent way to wake up the body. Going for a run or doing some aerobics releases stimulants into the body, which perks you up.
If you are injured or disabled, you can still benefit from exercise. Check out disability exercise tips.
Create a calm bedroom environment
Your bedroom should be for sleep only. Avoid turning it into an entertainment centre with televisions, computers and stereos.
Two thirds of children have a computer, games machine or TV in their bedroom and could be losing out on sleep as a result.
It’s fine to have a nightcap, but too much alcohol can make you restless. Alcohol is also a diuretic, which means it encourages you to urinate (never welcomed during the night).
Drinking is also more likely to lead to snoring, which can restrict airflow into the lungs. This reduces oxygen in your blood which disturbs your sleep and contributes to your hangover.
Caffeine is a stimulant which can stay in your system for many hours. So avoid sources of caffeine such as coffee, chocolate, cola drinks and non-herbal teas.
Watch what you eat
Eating a large heavy meal too close to bedtime will interfere with your sleep.
Spicy or fatty foods may cause heartburn, which leads to difficulty in falling asleep and discomfort throughout the night.
Foods containing tyramine (bacon, cheese, ham, aubergines, pepperoni, raspberries, avocado, nuts, soy sauce, red wine) might keep you awake at night. Tyramine causes the release of norepinephrine, a brain stimulant.
If you get the munchies close to bedtime, eat something that triggers the hormone serotonin, which makes you sleepy. Carbohydrates such as bread or grain, cereal will do the trick.
Set a regular bedtime and wake up time
Create a habit of going to bed and waking up at the same time each day, even on weekends. This helps anchor your body clock to these times. Resisting the urge for a lie-in can pay dividends in alertness.
If you feel you haven’t slept well, resist the urge to sleep in longer than normal; getting up on schedule keeps your body in its normal wake-up routine.
Remember, even after only four hours, the brain has gained many of the important benefits of sleep.
It’s only natural
Most of us have a natural dip in alertness between 2 – 4pm.
A 15 minute nap when you’re tired can be a very effective way of staying alert throughout the day. Avoid napping for longer than 20 minutes, after which you will enter deep sleep and feel even worse when you wake up.
See a doctor if your problem continues
If you have trouble falling asleep night after night, or if you always feel tired the next day, snore, or stop breathing during sleep you might have a sleep disorder. It is advisable to seek more advice from your doctor. Most sleep disorders can be treated effectively.
Leading neuroscientist Matthew Walker explains why sleep deprivation is increasing our risk of cancer, heart attack and Alzheimer’s – and what you can do about it.
Matthew Walker has learned to dread the question “What do you do?” At parties, it signals the end of his evening; thereafter, his new acquaintance will inevitably cling to him like ivy. On an aeroplane, it usually means that while everyone else watches movies or reads a thriller, he will find himself running an hours-long salon for the benefit of passengers and crew alike. “I’ve begun to lie,” he says. “Seriously. I just tell people I’m a dolphin trainer. It’s better for everyone.”
Walker is a sleep scientist. To be specific, he is the director of the Center for Human Sleep Science at the University of California, Berkeley, a research institute whose goal – possibly unachievable – is to understand everything about sleep’s impact on us, from birth to death, in sickness and health. No wonder, then, that people long for his counsel. As the line between work and leisure grows ever more blurred, it is rare to meet a person who doesn’t worry about their sleep. But even as we contemplate the shadows beneath our eyes, most of us don’t know the half of it – and perhaps this is the real reason he has stopped telling strangers how he makes his living. When Walker talks about sleep, he can’t in all conscience, limit himself to whispering comforting nothings about camomile tea and warm baths. It’s his conviction that we are in the midst of a “catastrophic sleep-loss epidemic”, the consequences of which are far graver than any of us could imagine. This situation, he believes, is only likely to change if government gets involved.
Walker has spent the last four and a half years writing Why We Sleep, a complex but urgent book that examines the effects of this epidemic close up, the idea being that once people know of the powerful links between sleep loss and, among other things, Alzheimer’s disease, cancer, diabetes, obesity and poor mental health, they will try harder to get the recommended eight hours a night (sleep deprivation, amazing as this may sound to Donald Trump types, constitutes anything less than seven hours). But, in the end, the individual can achieve only so much. Walker wants major institutions and law-makers to take up his ideas, too. “No aspect of our biology is left unscathed by sleep deprivation,” he says. “It sinks down into every possible nook and cranny. And yet no one is doing anything about it. Things have to change: in the workplace and our communities, our homes and families. But when did you ever see an NHS poster urging sleep on people? When did a doctor prescribe, not sleeping pills, but sleep itself? It needs to be prioritised, even incentivised. Sleep loss costs the UK economy over £30bn a year in lost revenue, or 2% of GDP. I could double the NHS budget if only they would institute policies to mandate or powerfully encourage sleep.”
Why, exactly, are we so sleep-deprived? What has happened over the course of the last 75 years? In 1942, less than 8% of the population was trying to survive on six hours or less sleep a night; in 2017, almost one in two people is. The reasons are seemingly obvious. “First, we electrified the night,” Walker says. “Light is a profound degrader of our sleep. Second, there is the issue of work: not only the porous borders between when you start and finish, but longer commuter times, too. No one wants to give up time with their family or entertainment, so they give up sleep instead. And anxiety plays a part. We’re a lonelier, more depressed society. Alcohol and caffeine are more widely available. All these are the enemies of sleep.”
But Walker believes, too, that in the developed world sleep is strongly associated with weakness, even shame. “We have stigmatised sleep with the label of laziness. We want to seem busy, and one way we express that is by proclaiming how little sleep we’re getting. It’s a badge of honour. When I give lectures, people will wait behind until there is no one around and then tell me quietly: ‘I seem to be one of those people who need eight or nine hours’ sleep.’ It’s embarrassing to say it in public. They would rather wait 45 minutes for the confessional. They’re convinced that they’re abnormal, and why wouldn’t they be? We chastise people for sleeping what are, after all, only sufficient amounts. We think of them as slothful. No one would look at an infant baby asleep, and say ‘What a lazy baby!’ We know sleeping is non-negotiable for a baby. But that notion is quickly abandoned [as we grow up]. Humans are the only species that deliberately deprive themselves of sleep for no apparent reason.” In case you’re wondering, the number of people who can survive on five hours of sleep or less without any impairment, expressed as a percent of the population and rounded to a whole number, is zero.
The world of sleep science is still relatively small. But it is growing exponentially, thanks both to demand (the multifarious and growing pressures caused by the epidemic) and to new technology (such as electrical and magnetic brain stimulators), which enables researchers to have what Walker describes as “VIP access” to the sleeping brain. Walker, who is 44 and was born in Liverpool, has been in the field for more than 20 years, having published his first research paper at the age of just 21. “I would love to tell you that I was fascinated by conscious states from childhood,” he says. “But in truth, it was accidental.” He started out studying for a medical degree in Nottingham. But having discovered that doctoring wasn’t for him – he was more enthralled by questions than by answers – he switched to neuroscience, and after graduation, began a PhD in neurophysiology supported by the Medical Research Council. It was while working on this that he stumbled into the realm of sleep.
“I was looking at the brainwave patterns of people with different forms of dementia, but I was failing miserably at finding any difference between them,” he recalls now. One night, however, he read a scientific paper that changed everything. It described which parts of the brain were being attacked by these different types of dementia: “Some were attacking parts of the brain that had to do with controlled sleep, while other types left those sleep centres unaffected. I realised my mistake. I had been measuring the brainwave activity of my patients while they were awake, when I should have been doing so while they were asleep.” Over the next six months, Walker taught himself how to set up a sleep laboratory and, sure enough, the recordings he made in it subsequently spoke loudly of a clear difference between patients. Sleep, it seemed, could be a new early diagnostic litmus test for different subtypes of dementia.
After this, sleep became his obsession. “Only then did I ask: what is this thing called sleep, and what does it do? I was always curious, annoyingly so, but when I started to read about sleep, I would look up and hours would have gone by. No one could answer the simple question: why do we sleep? That seemed to me to be the greatest scientific mystery. I was going to attack it, and I was going to do that in two years. But I was naive. I didn’t realise that some of the greatest scientific minds had been trying to do the same thing for their entire careers. That was two decades ago, and I’m still cracking away.” After gaining his doctorate, he moved to the US. Formerly a professor of psychiatry at Harvard Medical School, he is now professor of neuroscience and psychology at the University of California.
Does his obsession extend to the bedroom? Does he take his own advice when it comes to sleep? “Yes. I give myself a non-negotiable eight-hour sleep opportunity every night, and I keep very regular hours: if there is one thing I tell people, it’s to go to bed and to wake up at the same time every day, no matter what. I take my sleep incredibly seriously because I have seen the evidence. Once you know that after just one night of only four or five hours’ sleep, your natural killer cells – the ones that attack the cancer cells that appear in your body every day – drop by 70%, or that a lack of sleep is linked to cancer of the bowel, prostate and breast, or even just that the World Health Organisation has classed any form of night-time shift work as a probable carcinogen, how could you do anything else?”
There is, however, a sting in the tale. Should his eyelids fail to close, Walker admits that he can be a touch “Woody Allen-neurotic”. When, for instance, he came to London over the summer, he found himself jet-lagged and wide awake in his hotel room at two o’clock in the morning. His problem then, as always in these situations, was that he knew too much. His brain began to race. “I thought: my orexin isn’t being turned off, the sensory gate of my thalamus is wedged open, my dorsolateral prefrontal cortex won’t shut down, and my melatonin surge won’t happen for another seven hours.” What did he do? In the end, it seems, even world experts in sleep act just like the rest of us when struck by the curse of insomnia. He turned on a light and read for a while.
Will “Why We Sleep” have the impact its author hopes? I’m not sure: the science bits, it must be said, require some concentration. But what I can tell you is that it had a powerful effect on me. After reading it, I was absolutely determined to go to bed earlier – a regime to which I am sticking determinedly. In a way, I was prepared for this. I first encountered Walker some months ago, when he spoke at an event at Somerset House in London, and he struck me then as both passionate and convincing (our later interview takes place via Skype from the basement of his “sleep centre”, a spot which, with its bedrooms off a long corridor, apparently resembles the ward of a private hospital). But in another way, it was unexpected. I am mostly immune to health advice. Inside my head, there is always a voice that says “just enjoy life while it lasts”.
The evidence Walker presents, however, is enough to send anyone early to bed. It’s no kind of choice at all. Without sleep, there is low energy and disease. With sleep, there is vitality and health. More than 20 large scale epidemiological studies all report the same clear relationship: the shorter your sleep, the shorter your life. To take just one example, adults aged 45 years or older who sleep less than six hours a night are 200% more likely to have a heart attack or stroke in their lifetime, as compared with those sleeping seven or eight hours a night (part of the reason for this has to do with blood pressure: even just one night of modest sleep reduction will speed the rate of a person’s heart, hour upon hour, and significantly increase their blood pressure).
A lack of sleep also appears to hijack the body’s effective control of blood sugar, the cells of the sleep-deprived appearing, in experiments, to become less responsive to insulin, and thus to cause a prediabetic state of hyperglycaemia. When your sleep becomes short, moreover, you are susceptible to weight gain. Among the reasons for this are the fact that inadequate sleep decreases levels of the satiety-signalling hormone, leptin, and increases levels of the hunger-signalling hormone, ghrelin. “I’m not going to say that the obesity crisis is caused by the sleep-loss epidemic alone,” says Walker. “It’s not. However, processed food and sedentary lifestyles do not adequately explain its rise. Something is missing. It’s now clear that sleep is that third ingredient.” Tiredness, of course, also affects motivation.
Sleep has a powerful effect on the immune system, which is why, when we have flu, our first instinct is to go to bed: our body is trying to sleep itself well. Reduce sleep even for a single night, and your resilience is drastically reduced. If you are tired, you are more likely to catch a cold. The well-rested also respond better to the flu vaccine. As Walker has already said, more gravely, studies show that short sleep can affect our cancer-fighting immune cells. A number of epidemiological studies have reported that night-time shift work and the disruption to circadian sleep and rhythms that it causes increase the odds of developing cancers including breast, prostate, endometrium and colon.
Getting too little sleep across the adult lifespan will significantly raise your risk of developing Alzheimer’s disease. The reasons for this are difficult to summarise, but in essence it has to do with the amyloid deposits (a toxin protein) that accumulate in the brains of those suffering from the disease, killing the surrounding cells. During deep sleep, such deposits are effectively cleaned from the brain. What occurs in an Alzheimer’s patient is a kind of vicious circle. Without sufficient sleep, these plaques build up, especially in the brain’s deep-sleep-generating regions, attacking and degrading them. The loss of deep sleep caused by this assault therefore lessens our ability to remove them from the brain at night. More amyloid, less deep sleep; less deep sleep, more amyloid, and so on. (In his book, Walker notes “unscientifically” that he has always found it curious that Margaret Thatcher and Ronald Reagan, both of whom were vocal about how little sleep they needed, both went on to develop the disease; it is, moreover, a myth that older adults need less sleep.) Away from dementia, sleep aids our ability to make new memories, and restores our capacity for learning.
And then there is sleep’s effect on mental health. When your mother told you that everything would look better in the morning, she was wise. Walker’s book includes a long section on dreams (which, says Walker, contrary to Dr Freud, cannot be analysed). Here he details the various ways in which the dream state connects to creativity. He also suggests that dreaming is a soothing balm. If we sleep to remember (see above), then we also sleep to forget. Deep sleep – the part when we begin to dream – is a therapeutic state during which we cast off the emotional charge of our experiences, making them easier to bear. Sleep, or a lack of it, also affects our mood more generally. Brain scans carried out by Walker revealed a 60% amplification in the reactivity of the amygdala – a key spot for triggering anger and rage – in those who were sleep-deprived. In children, sleeplessness has been linked to aggression and bullying; in adolescents, to suicidal thoughts. Insufficient sleep is also associated with relapse in addiction disorders. A prevailing view in psychiatry is that mental disorders cause sleep disruption. But Walker believes it is, in fact, a two-way street. Regulated sleep can improve the health of, for instance, those with bipolar disorder.
I’ve mentioned deep sleep in this (too brief) summary several times. What is it, exactly? We sleep in 90-minute cycles, and it’s only towards the end of each one of these that we go into deep sleep. Each cycle comprises two kinds of sleep. First, there is NREM sleep (non-rapid eye movement sleep); this is then followed by REM (rapid eye movement) sleep. When Walker talks about these cycles, which still have their mysteries, his voice changes. He sounds bewitched, almost dazed.
“During NREM sleep, your brain goes into this incredible synchronised pattern of rhythmic chanting,” he says. “There’s a remarkable unity across the surface of the brain, like a deep, slow mantra. Researchers were once fooled that this state was similar to a coma. But nothing could be further from the truth. Vast amounts of memory processing is going on. To produce these brainwaves, hundreds of thousands of cells all sing together, and then go silent, and on and on. Meanwhile, your body settles into this lovely low state of energy, the best blood-pressure medicine you could ever hope for. REM sleep, on the other hand, is sometimes known as paradoxical sleep, because the brain patterns are identical to when you’re awake. It’s an incredibly active brain state. Your heart and nervous system go through spurts of activity: we’re still not exactly sure why.”
Does the 90-minute cycle mean that so-called power naps are worthless? “They can take the edge off basic sleepiness. But you need 90 minutes to get to deep sleep, and one cycle isn’t enough to do all the work. You need four or five cycles to get all the benefit.” Is it possible to have too much sleep? This is unclear. “There is no good evidence at the moment. But I do think 14 hours is too much. Too much water can kill you, and too much food, and I think ultimately the same will prove to be true for sleep.” How is it possible to tell if a person is sleep-deprived? Walker thinks we should trust our instincts. Those who would sleep on if their alarm clock was turned off are simply not getting enough. Ditto those who need caffeine in the afternoon to stay awake. “I see it all the time,” he says. “I get on a flight at 10am when people should be at peak alert, and I look around, and half of the plane has immediately fallen asleep.”
So what can the individual do? First, they should avoid pulling “all-nighters”, at their desks or on the dancefloor. After being awake for 19 hours, you’re as cognitively impaired as someone who is drunk. Second, they should start thinking about sleep as a kind of work, like going to the gym (with the key difference that it is both free and, if you’re me, enjoyable). “People use alarms to wake up,” Walker says. “So why don’t we have a bedtime alarm to tell us we’ve got half an hour, that we should start cycling down?” We should start thinking of midnight more in terms of its original meaning: as the middle of the night. Schools should consider later starts for students; such delays correlate with improved IQs. Companies should think about rewarding sleep. Productivity will rise, and motivation, creativity and even levels of honesty will be improved. Sleep can be measured using tracking devices, and some far-sighted companies in the US already give employees time off if they clock enough of it. Sleeping pills, by the way, are to be avoided. Among other things, they can have a deleterious effect on memory.
Those who are focused on so-called “clean” sleep are determined to outlaw mobiles and computers from the bedroom – and quite right, too, given the effect of LED-emitting devices on melatonin, the sleep-inducing hormone. Ultimately, though, Walker believes that technology will be sleep’s saviour. “There is going to be a revolution in the quantified self in industrial nations,” he says. “We will know everything about our bodies from one day to the next in high fidelity. That will be a seismic shift, and we will then start to develop methods by which we can amplify different components of human sleep, and do that from the bedside. Sleep will come to be seen as a preventive medicine.”
What questions does Walker still most want to answer? For a while, he is quiet. “It’s so difficult,” he says, with a sigh. “There are so many. I would still like to know where we go, psychologically and physiologically, when we dream. Dreaming is the second state of human consciousness, and we have only scratched the surface so far. But I would also like to find out when sleep emerged. I like to posit a ridiculous theory, which is: perhaps sleep did not evolve. Perhaps it was the thing from which wakefulness emerged.” He laughs. “If I could have some kind of medical Tardis and go back in time to look at that, well, I would sleep better at night.”
Sleep in numbers:
■ Two-thirds of adults in developed nations fail to obtain the nightly eight hours of sleep recommended by the World Health Organisation.
■ An adult sleeping only 6.75 hours a night would be predicted to live only to their early 60s without medical intervention.
■ A 2013 study reported that men who slept too little had a sperm count 29% lower than those who regularly get a full and restful night’s sleep.
■ If you drive a car when you have had less than five hours’ sleep, you are 4.3 times more likely to be involved in a crash. If you drive having had four hours, you are 11.5 times more likely to be involved in an accident.
■ A hot bath aids sleep not because it makes you warm, but because your dilated blood vessels radiate inner heat, and your core body temperature drops. To successfully initiate sleep, your core temperature needs to drop about 1C.
■ The time taken to reach physical exhaustion by athletes who obtain anything less than eight hours of sleep, and especially less than six hours, drops by 10-30%.
■ There are now more than 100 diagnosed sleep disorders, of which insomnia is the most common.
■ Morning types, who prefer to awake at or around dawn, make up about 40% of the population. Evening types, who prefer to go to bed late and wake up late, account for about 30%. The remaining 30% lie somewhere in between.