City Arts & Lectures: Why do humans sleep? What is sleep’s evolutionary basis and what really is going on when we do it? This week, we’re broadcasting a conversation with cognitive neuroscientist Matthew Walker, talking to Dr. Indre Viskontas in 2015. An expert on the science of sleep, Walker’s research reveals that every tissue in the body and every process within the brain is enhanced as we sleep and impaired when we aren’t sleeping enough. His research also examines the effects of stress, sleeping aids, and alcohol, and the ways we can improve our sleeping habits. Join us now for a conversation with Matthew Walker on the science of sleep.
Indre Viskontas: So sleep. It’s kind of a ridiculous thing to do. Why do we sleep? Why, why has evolution allowed this behavior to continue to be a part of our lives?
Matthew Walker: Until very recently, we actually didn’t have the answer as to why we sleep. Although I take that back, we actually did have an answer. It was profoundly crass. It was delightfully un-useful and it was this: we sleep to cure sleepiness. Which is, which is like saying the reason that you need food, the reason that you need sustenance, is to stop hunger. You know, that tells you nothing about the role that food plays in biochemical nourishment. You know, so, so until recently we didn’t have a full understanding.
But your point is actually an interesting one, which is why did it appear in the first place? What we certainly know is that every species that we’ve studied to date sleeps, even old evolutionary organisms, things like worms, for example. Worms actually do sleep. What that means is that sleep appeared to evolve with life itself on this planet. And after it did, it has fought its way through heroically, every step along the evolutionary path. And if that’s true, it must mean that sleep is fundamentally important at the most basic of biological level. But what’s odd is that when you look at it, you think, but that’s a dumb idea. Because firstly I’m, you know, I’m not gathering resources, I’m not finding a mate, I’m not reproducing, I’m not actively socializing, and worse still, I’m vulnerable to predation. You know, on any one of those grounds, you know, sleep should have been strongly selected against. On all of those grounds put together, what are we doing? If sleep– and this is a great quote from a founding father of the field– if sleep doesn’t serve an essential function, it’s the biggest mistake evolution ever made.
Indre Viskontas: Absolutely.
Matthew Walker: And now we understand that it serves a whole multitude of different functions, both for the brain and for the body.
Indre Viskontas: So let’s get into some of those. What does it do? Let’s start with the body. What is, what does it do for the body?
Matthew Walker: Yes. So one of the ways that we try to sort of understand what sleep does is to take sleep away and then observe what happens in terms of the catastrophe that are the impairments following sleep deprivation. And the short answer is this, there isn’t a single tissue within the body or process within the brain that isn’t enhanced by sleep when you get it, or fundamentally impaired when you don’t get enough.
Let me give you some examples within the body. So first, one of the things that sleep is critical for is the regulation of your metabolism, particularly of glucose. So glucose is the principle energy source for many of the cells in your body, and also, when you’re young in the brain. What you always want is a nicely regulated concentration of glucose within the body, and you have wonderful systems to try and do that. If I take you and I don’t totally sleep deprive you for an entire night, I just restrict your sleep to let’s say, five hours for five nights. Your glucose regulation is so impaired, that at that point, your doctor would classify you as pre-diabetic.
Indre Viskontas: That’s amazing.
Matthew Walker: So that’s metabolism. You can also think about it from the state of the immune system. And this is one of the, I think, sort of revolutionary domains of research in recent years. If I were to, again, just take you and not deprive you of totally of sleep, but for one night restrict your sleep to four hours. And then I’m going to look to see what percent reduction in immune cell activity you’re suffering. And here in this study, they were looking at a particular immune cell, it’s called a natural killer cell. Sounds fantastic. It’s a great name for like a death metal band. But so, but so natural killer cells, you could think of like the secret service agents of your immune system. They’re very good at identifying dangerous foreign elements and eliminating them. And one of the things that they do very well is embed themselves into malignant cancerous, tumor masses, and destroy them. So what you want is a virile set of these immune cells at all times. And that’s exactly what you don’t have if you’re not sleeping.
So if I take sleep away for one night or restrict it to four hours, as I said, the percent reduction is not small. It’s not 10%. It’s not 20%. There is a 70% reduction in natural killer cell activity. And it happens quickly, essentially after just one bad night of sleep. So imagine the state after weeks, if not months. And you may not then find it surprising that a lack of sleep is a significant risk factor for the development of numerous forms of cancer.
And the piece of evidence that I think strikes people hardest is to realize that recently the World Health Organization decided to classify shift work, because of the disruption of your sleep rhythms, as a probable carcinogen. Jobs that will induce cancer because of sleep disruption. So that old maxim, “I’ll sleep when I’m dead,” is mortally unwise advice. Very seriously.
It is, you know, you will be, we know the evidence now. If you adopt that mindset, you will be dead sooner. And the quality of that now shorter life will be significantly worse.
Indre Viskontas: And yet it seems as though we can’t really make up for the lost sleep. And that seems to be an evolutionary mistake too. I mean, why can’t we just make it up?
Matthew Walker: Right. So what’s interesting is that if I take sleep away from you for an entire night, so you lose a total of eight hours of sleep, and then I let you sleep all that you want on the next night, and the next night after that, yes, you will sleep longer than you would normally on those subsequent, what we call recovery nights, but you never get back all that you lost in the first night.
What that means is that the system has no capacity to regain sleep that was removed. In other words, sleep– and this is a common mistake– sleep is not like a credit system. Sleep is not like the bank. You cannot accumulate a debt, and then hope to pay it off at some later point in time. And the way people do this, at least my students that I, my undergraduates, they have what I would describe as sleep bulimia, which is that during the week, you know, nobody wants to go to bed any earlier, but they have to wake up early for classes. And then at the weekend they just binge on sleep: 10 hours, 11 hours. So it’s a real binge purge. It’s I mean, it’s like a sleep bulimia, so, but it’s a profoundly wrong notion.
And you could ask the question, and you did, which is great. Why hasn’t evolution put in place the ability to regain sleep at a time when you can, you know, get that sleep? And the answer is this: human beings seem to be the only species that deliberately deprive themselves of sleep for no adaptive benefit. With the exception of a small sparrow that I would love for us to return to in just a second, that I kid you not. But my point is a quite serious one, however, which is that evolution as a consequence has never faced the challenge of having to deal with sleep deprivation. No other species does that. As a consequence, there is no safety net that Mother Nature has evolved to get back the missed sleep. Cause no species has ever done that before. Why would it be coming up with solutions to problems that don’t exist with the exception of humans?
Indre Viskontas: So what do other species do? I mean, surely we don’t all have the same sleep patterns. What can we learn from the sleep patterns of other species that helps us understand why we sleep the way we do?
Matthew Walker: So that actually is one of the remaining mysteries of the sleep field. Is firstly that we know that– is profound variability from one species to the next, even within categories across the animal kingdom. Just take mammals for example. So, you know, elephants will sleep perhaps just four hours. Human beings will sleep eight hours, a little brown bat, will sleep almost 20 hours out of the 24. And you would think that there would be a very clear, obvious reason that explains that variability in total sleep time. And we cannot find it. It’s, it’s a strange, sort of a tough puzzle to solve. There are things that explain a little bit of, of the variants. Very little though. So. Usually that tells you that you’re asking the wrong question. It’s probably that total sleep time itself is maybe not the measure that we should be using to think about sleep as explained from one species to the next. Maybe it’s about quality of sleep and not just quantity, or maybe it’s the combination of those two. And so I think that’s where the field is moving. But lots of variability throughout sleep, but explanation not yet known.
There is fascinating variability though, that we do know a little bit about, which is not sleep amount, but how the brain sleeps. Some species will sleep with half a brain. So dolphins, for example, they will go to sleep with one half of their brain and keep the other for mobility. They, marine mammals need to keep moving. If both hemispheres, both halves of the brain fell asleep, that movement would stop. Now birds also have this type of sleep too. It’s what we call unihemispheric sleep. Scientists love to give long names to sort of make themselves feel like… they’re just sleeping with half a brain. That’s what it means.
But birds do that too, but for a very different reason. There, it’s about safety. So if you get a flock of birds and they all line up on the branch of a tree, something remarkable happens. All of the birds in the middle will sleep with both hemispheres. They will have– both sides of their brain will sleep. The guys on the end, the guards, as it were, they will sleep with half of a brain. And the opposite half in each of them. That means that the other half of the brain that is awake allows the eye to be open and giving threat detection. So now you’ve got a whole row of birds. You’ve got 360 degrees of panoramic threat detection because you’ve got one eye and one half of the brain paying attention to 180 degrees on the left side. Same on the right. Now, what happens is that once those guys have taken their fill of sleep, for that one half of the brain, they stand up, they rotate 180 degrees, they sit back down again, and the other side of the brain gets to sleep. Isn’t that incredible? And what that tells you is that sleep is so important, Mother Nature would create a remarkable ballet of behavior and brain wiring to still get that sleep. That’s how important sleep must be.
Indre Viskontas: And how did those poor sods get left out on the ends there?
Matthew Walker: Yeah. Well, that’s the question. I still don’t think it’s clear that there is some rotational mechanism, you know, come on guys. I was doing this yesterday and you guys are still in the middle, of what’s? You know, equity in the avian world.
Indre Viskontas: So if it’s not about quantity, let’s talk about the quality. What’s going on in our brains when we’re sleeping and how do we understand the different stages of sleep?
Matthew Walker: Yes, so human beings, and in fact, all mammalian species, have two types of sleep. On the one hand we have what’s called non rapid eye movement sleep, or non REM sleep for short. And non- REM sleep has been further subdivided into four separate stages, and they are unimaginatively called stages one through four. We’re a creative bunch, us sleep researchers. So. And they are increasing in depth of sleep. So stages three and four are those really deep stages of restorative sleep. On the other hand, the second stage of principal sleep is called rapid eye movement sleep or REM sleep. And that’s named not after the popular Michael Stipe pop band, but because of these bizarre horizontal eye movements that occur during this stage of sleep, these rapid eye movements back and forth, back and forth.
And it turns out that those two types of sleep will play out in a battle for brain domination throughout the night. And that cerebral war is going to be won and lost, in humans at least, every 90 minutes, and then replayed every 90 minutes, to create a cycling structure of sleep. So when you first fall asleep, you go into the light stages of non-REM. Then down into the deep stages, three and four of that really deep sleep. And then after about 70 or 80 minutes, you’ll start to rise back up, and you’ll pop up and have a short REM sleep period. And then back down, you go again, down into non- REM up into REM. That 90 minutes cycle remains constant across the night. What changes, however, is the ratio of non-REM to REM, within that 90 minutes cycle, as you move across the night. Such that in the first half of the night, the majority of those 90 minute cycles are comprised of lots of deep non- REM sleep and very little REM. As you push through to the second half of the night, that seesaw balance shifts over, and instead those 90 minutes cycles are comprised of much more rapid eye movement sleep. And it’s the rapid eye movement sleep that principally produces dreaming. That’s REM sleep is mostly dream sleep, and we can speak about dreaming, which is a bizarre state too, but, but that’s how the structure of sleep is produced across a night.
What’s strange is that we don’t know why. Why, why do you always have to have non REM sleep first and REM sleep second? Why should you have this strange oscillating set of sleep throughout the night and an imbalance– more of one first, more of the other later?
Indre Viskontas: Well, what is it that differentiates the stages? I mean, can we see evidence in the brain that someone is in one stage versus versus another? And do we know what that stage is for, in terms of either what’s happening in the body or the brain, or both?
Matthew Walker: Yeah. So I think what science has done a remarkable job of is dismantling the different stages of sleep, and then essentially understanding what each of those sleep stages provides in terms of a function. And we can now hang little labels, functional labels, onto all of those different stages of sleep. So I can tell you that that deep sleep is very good for learning and memory. The REM sleep is important for creativity. It’s important for emotional regulation, it’s overnight therapy. So we’ve done a wonderful job of understanding what those functions are, regarding the different stages of sleep. But again, what we still don’t understand is why they fit together in this bizarre sort of timeline of interaction. It’s very specific and every species follows this patent non- REM, REM, non- REM, REM. So it’s repeatable and it’s reliable across phylogeny. It must mean that there is some kind of DaVinci code in the that we don’t yet understand, but we certainly now do understand many of the different functions of those different stages of sleep.
Indre Viskontas: And do many species also spend more time in the beginning of the night in deeper stages, stages three and four, for example, and more time at the end of the night, or however long their night is, in REM? Or is that really a human thing?
Matthew Walker: No, it’s common, certainly across the mammalian and even in the avian kingdom. So it turns out that not all species have REM sleep. Only birds and mammals seem to have reliable REM sleep. Amphibians, fish, insects: they have what seems to be non rapid eye movement sleep. They don’t have REM sleep. And of course, birds and mammals evolved later in that trajectory of evolution. So it tells us that REM sleep, dream sleep, is the new kid on the block in terms of sleep, when it comes to its evolutionary age.
Indre Viskontas: So what’s happening then in the deeper stages of, you know, three and four that–I mean, can we tell how exactly that enhances learning and memory and other features that we might share with these other species?
Matthew Walker: Yes. So we now know that during that deepest stage of sleep, stages, three and four, it’s also called in the sleep community, slow wave sleep. And the reason is because you get these huge, enormous, slow brain waves that happen. Incredibly powerful, large brainwaves. And it’s a very synchronous rhythm. So when we’re all awake, as at least 20% of the audience is at this stage, different parts– I think my brain is such a potent sedative . Most my, my, my voice. So.
During the day when your brain is awake, different parts of your brain are processing information at different moments in time and performing different functions. As a consequence, your brain is what we call desynchronized in its activity. The analogy would be a football stadium before a big game. You know, when the crowd is in there before the game starts, you know, everyone’s having their separate conversations and you don’t really hear a clear, powerful signal coming from the stadium. But let’s say this is a Berkeley football stadium and they’re playing Stanford and the game gets underway. Now the entire crowd is synchronized in a unison, singular voice, saying Stanford sucks. They’re chanting that. Okay. Or, or no, no, no, no. Or, or Berkeley sucks, if you’re at Stanford. I am. I am. I think Stanford’s great. Now. So as I will never be let back into the Berkeley campus.
What that, so what that means is that hundreds of thousands of voices have all synchronized themselves in time. In their signal. That’s what happens during the deepest stages of sleep. Hundreds of thousands of cells within your brain, all decide to start chanting in this slow mantra fashion. And why, we don’t fully understand. But it’s utterly unique. What we now start to think, however, that type of synchronized brainwave activity supports, is a file transfer mechanism. It allows you to shift information from one storage location, a temporary short-term storage location, to a different geographical location within the brain, a more permanent storage location. So the analogy would be a USB stick in a hard drive.
There’s a part of the brain called the hippocampus, which you know, very well. Indre has been a pioneer in studying this structure, it turns out. And it’s very, it’s like the memory inbox of your brain. It’s great at grabbing new files and binding them together. But what we also know is that at night, that hippocampus, that inbox, which is like the USB stick, will then transfer its memory files of the day out into the hard drive of your brain, which is called the cortex, which is this folded massive tissue that sits on top of your brain.
And this deep sleep seems to promote a therapy session. A sort of a dialogue between these two structures. And so you transfer, there is sort of a, you know, really a, real estate transaction of information happens at night.
Indre Viskontas: And there’s these lovely studies of you know, people who study something and then they take a nap and, or they don’t do anything. And then it turns out that they can remember better if they’ve taken a nap, but that falls away after 24 hours in some cases, because you’ve been able to go into sleep. Is that really part of the job of, of stages three and four? Is it to also help us forget the things that are irrelevant during the day? Do we see any evidence of, of kind of, you know, people who are sleep deprived, showing memory intrusions of things that they should have forgotten, that now they’re confused by, or do we just see that they just don’t remember what they should have remembered?
Matthew Walker: Yeah. So we used to think that sleep was a bit of a blunt instrument when it comes to learning and memory. That everything that you experienced during the day was essentially going to get cemented. So it’s like hitting the save button on all of the files that you’ve aggregated. Now we understand that sleep is far more intelligent, that sleep can actually transact both remembering and forgetting. And it uses what we call salience tags. So if there are things that seem to be novel or things that are especially emotional, the brain tends to latch onto those things and promote them in terms of remembering. Things that seem to be trivial, that are not salient, that are not emotional, that are not important to you, the organism, sleep seems to let go of them, and if anything, will actually remove them. And you think, well, hang on a second. The function of memory is always to remember. That’s not true. I mean, forgetting is probably the price that we pay for accurate remembering. You know, imagine remembering every parking spot, when you’re trying to remember today, where you parked your car. Not so smart, is it. And the brain has a system for that. And sleep seems to be part of that intelligent memory system design.
Indre Viskontas: So if that’s what’s happening in sort of the earlier stages of the night, what’s happening during REM? Particularly as you mentioned that that might be involved in creativity.
Matthew Walker: Yes. So REM sleep is the principle stage from which you dream. And one of the hard things is to try and figure out what is dream specific, in terms of a function, and what is simply REM sleep specific. Because those two things are isomorphic. You can’t really have dreams without REM sleep. So it’s sometimes hard to put a wedge between those two. But let’s speak about it for now as sort of dream sleep, REM sleep.
Firstly, by the way, I should note that dreaming is a striking state of psychosis. In fact, everyone here, as long as you slept last night and I hope you did, you all became flagrantly psychotic. Now, before you reject my diagnosis, let me give you five good reasons. Last night, when you were dreaming, you started to see things which were not there. So you were hallucinating. Second, you believe things that couldn’t possibly be true. So you were delusional. Third, you became confused about time, about place, and about person. So you’re suffering from disorientation. Fourth, you had wildly fluctuating emotions. Something that psychiatrists call being as affectively labile. And then, how wonderful, you woke up this morning and you forgot most, if not all of that dream experience. So you’re suffering from amnesia. If you were to experience any one of those five symptoms while you’re awake, you would be seeking psychiatric intervention. But yet for reasons that seem to be perfectly normal, it’s a biological and psychological necessity.
The question then is, well, what what’s going on? What would be the function of that type of mental conscious experience? One of the things that we’ve discovered is that sleep and including dream sleep is critical for creativity. That sleep will offer about a threefold advantage in problem solving creative capacity, then the same amount of time simply spent awake. And it’s perhaps not surprising as a consequence, nobody has ever told you, you should stay awake on a problem, right? People tell you to sleep on a problem. And we’re finding the scientific proof that supports exactly that. What I should also note by the way, is that every language that I’ve inquired about to date, that phrase exists, sleeping on a problem. What that means is that the creative benefit of dream sleep transcends cultural boundaries. It’s common across the globe.
What I should note is that we, the British, we say, say you sleep on a problem. The French translation is much closer to you sleep with a problem. So British you sleep on a problem, French you sleep with a problem, I think it says so much about the romantic difference, between the British and the French.
But this this there’s a great there’s a great story. Often when I sort of tell people about the creative benefits of sleep, they’ll say, well, aren’t there those creative genius types in history who are supposed to have been short sleepers. How does that square with what you’re telling me? And one that’s often quoted to me is Thomas Edison. Edison, who by the way, has a great deal to answer for, for how we’re sleeping or not sleeping in modern day society. But a brilliant man, nonetheless and Edison was supposed to be a short sleeper. Now we’ll never, of course know if he was or not, but even if he was, it turns out that Edison was a habitual napper during the day. And in fact, he understood the creative brilliance of sleep and he used it ruthlessly as a tool.
What he would do is sit in his study in his work chair and he would have a pad of paper and a pen next to him. And then he would pick up a metal saucepan, turn it upside down and place it underneath the armrest, and then he would pick up two steel ball bearings in his hand and rest his arm on the back of the chair, on the arm rest. And then gradually he would start to fall back and go to sleep. And so he didn’t fall too far into sleep. What would happen is that his muscle tone would relax, he would release the steel ball bearings, they would crash on the saucepan underneath them, wake him up, and then he would write down all of the ideas that he was having from sleep. Isn’t that brilliant?
Indre Viskontas: It is brilliant. And, and so maybe the big invention that he had that changed our sleep patterns forever, really weren’t a problem for him. So.
Matthew Walker: Exactly.
Indre Viskontas: Let’s talk about how people slept before Edison and how that’s changed.
Matthew Walker: Yes. So it’s actually a very interesting question, which is to say, how are we sleeping right now in in first world countries?
And how should we be sleeping? Are those two the same? And the answer perhaps is no. That right now across most industrialized nations, the way we sleep is in one single bout at night. It’s what we call monophasic sleep. One phase of sleep. If you look at cultures that are untouched by electricity, so if you look at the !Kung in the Kalahari desert, if you look at the Jabora, for example in Northern Kenya these are remarkably remote cultures, untouched, as I said, by Western civilization, they tend to sleep in what we call a biphasic pattern. They will have about six and a half hours of sleep a night from sort of midnight through until dawn. And then in the afternoon, they will have anywhere between 45 to 90 minutes of sleep, the siesta like behavior. And that seems to be perhaps how we were actually programmed to sleep, what’s called, as I said biphasically. And the reason, the argument is, that everyone here around two or three or 4:00 PM in the afternoon, if I have some measurement equipment on you, that I can assess your physiological alertness, you all show a pre-programmed genetically determined dip in your alertness. It’s that, you know, when you’ve sort of been around the boardroom table in meetings after lunch, and you sort of start to get all of these head nods going on, you know, it’s not people listening to good music, it’s that they’re falling prey to this hardwired dip in your alertness. It’s the siesta nap behavior.
What’s interesting is that back a few years ago in Greece, where they were still having this sort of siesta profile, at least the males were. Turns out females were now awake. They were about to abolish the siesta, the nap behavior pattern throughout society. And scientists said, well, okay, if you’re going to do that, can we study it? And rates of cardiovascular disease, of stroke, of diabetes, of anxiety, depression– these things skyrocketed as a consequence. And you can even see that sleep manipulation twice a year when we shift the clocks back and forward. When we shift the clocks and we lose an hour, that next day, heart attack rates spike, road traffic accidents, spike. When you add that hour of sleep, six months later, heart attacks drop the following day, road traffic accidents drop the following day. So we’re starting to understand that there is even, for small modifications of your sleep, it doesn’t have to be something catastrophic, small modifications cause marked changes.
And the reason that concerns me, is because right now, one out of every two Americans is trying to survive on seven hours of sleep or less, one in five of the people out on the street is trying to survive on six hours of sleep or less. So the decimation of sleep throughout industrialized nations is having a catastrophic impact on our health and our wellness. And it really is a sleep loss epidemic. It’s a silent one too.
Indre Viskontas: What is that magic number? How many hours a night should we be sleeping?
Matthew Walker: So right now, what we know is that human adults, the World Health organization currently recommends eight hours of sleep a night. And a lot of people have a reaction to that, really? That, and it’s the same reaction that people have if you say, well, Matt, how much do you sleep? And I say, you know, usually about, you know, eight, eight and a half hours. People look at you, you know, there’s a slight sort of… and the reason that they have that reaction of really? Is because we in my field of sleep have an image problem. Right now we equate sufficient sleep with laziness. It is a terrible, terrible stigma, and it’s doing real harm to our medical health. And what’s strange is that we don’t always have that opinion. The example would be, nobody looks at an infant sleeping during the day and says, what a lazy baby.
Indre Viskontas: I wish my baby was lazier.
Matthew Walker: But. We don’t. Why, why don’t we do that? We don’t do that because we know at that time of life, sleep is fundamentally important. What’s frightening is that somewhere between infancy and even now childhood, we abandon the notion that sleep is important, and worse, we stigmatize it. In fact, we are proud to report how little sleep we’re getting. And I think we are with our state of sleep deprivation where we were with smoking 30 years ago. All of the science was there, we knew that smoking was carcinogenic. We knew that it caused cancer, but the public health message had not gone out. Governments had not implemented policies. And as a consequence for that intermediary 30 years of time before we started to do something about it, people had terrible health. People were dying. That is the current state with sleep deprivation. And I think we need to shift into that mindset of our battle with smoking and cancer. I mean, back then, you know, you could turn on the television and, you know, people were promoting smoking as something that was cool, you know, commercials with, there were even race cars going around tracks that were sponsored by big tobacco companies.
You see that right now with sleep deprivation in modern society, it’s promoted as something that you can be proud of. And I think what’s interesting about the smoking model, is that, in the last 10 years, we switched from trying to treat all of the problems that were coming from smoking, to a model of prevention, which is to remove smoking from the public domain. That’s what we need to do with sleep right now. If we don’t want to suffer 30 years of terrible mortality morbidity rates, we need to shift our mindset away from simply treating, which is what we’re doing now. The snapped elastic band of sleep deprivation. And it can only stretch so far, and it’s snapped now– to a model of prevention, which is where we reclaim our rights to a full night of sleep without embarrassment. And without that stigma.
Indre Viskontas: And maybe one place to start is with the kids, just like, you know, probably the first person you take a cigarette away from the child. You know, we have now this movement to try to change the timing of schooling of, of when school starts and so forth. So what do you think should be an ideal school schedule that we should adopt?
Matthew Walker: Yeah. Well, considering what we now know about the importance of sleep for learning and memory and how critical it actually is, I think the educational domain is perhaps one of the areas of strongest importance. That together with perhaps old age and dementia, which we can speak about too, where there’s a strong sleep link. But there is, there is now a movement and it it’s a trickling movement and it needs to accelerate for later school start times for teens and adolescents. And let me just give you one study that convinced me. The study was done in a township called Edina, which is in Minnesota, just outside of Minneapolis. They shifted the school start times for their teens from seven thirty in the morning to eight twenty-five in the morning. By the way, what are we trying to do to educate teenagers at seven twenty-five in the…?
But anyway, so here’s, here’s the data. They looked at the top performing students the year before they made the time switch. And for those top performing students, their SAT score was 1,288, which is a great score. The following year, when they shifted the school start times to eight twenty-five, the only thing that was more impressive than the extra 43 minutes of sleep that those kids reported getting, was their change in SAT score. That same top percent performing students, that same top percent group, their SAT score was 1,500. That is a non trivial increase. That will change which university ultimately those students go to and probably the trajectory of their lives. Why are we doing this to our youth? We are hamstringing them in terms of their education. And it’s also not fair on the teachers. We should not expect teachers to be going into a classroom and trying to infuse sleep deprived brains. If our goal as educators is to educate, we need to change our view of sleep.
Indre Viskontas: So how does sleep change across the lifespan? And is it as the, as you get older, is it just that we get busier, or are there actual brain changes that we can measure that make us less good at sleeping?
Matthew Walker: So it’s certainly the latter. Across the lifespan sleep does change and it changes dramatically. It changes from infancy to childhood, to adulthood, and then into old age. One of the things that starts to deteriorate in terms of your sleep, and it deteriorates early on, is that deep sleep that’s important for learning and memory. Even by the time you’re in your early thirties, I can already measure reductions to your deep sleep. By the time you’re 50, you have about 50% less of the deep sleep that you had when you were a teenager. By the time you’re 70, you have about 5% of that deep sleep left. Now, what we of course know is that as we get older, our learning and memory capacity starts to decline. And what I’ve just told you is that as we get older, we also know that our sleep starts to deteriorate. And just recently we published evidence that those two things are not simply co-occurring, they are significantly interrelated. It suggests that sleep disruption is an underappreciated factor that is contributing to memory problems as we get older. And now it seems in dementia as well. Now I know that sounds remarkably depressing. But there’s a silver lining. We can do something about sleep. Sleep is a treatable target. So unlike many of the other features of the aging brain– changes in blood flow or changes to the structure of the brain– they are fiendishly difficult to treat. Medicine doesn’t have a good ways to alter them. We do have ways to modify sleep. And so I think it’s it’s an optimistic possibility. And we’re trying to do that now.
There is actually a device that we’re using called a transcranial direct current brain stimulation device. It’s again, why neuroscience has to come up with … it’s a brain stimulator, okay. And it sounds like science fiction, but it’s science fact. If I apply this stimulator, and it’s a little box, it’s a portable, affordable piece of technology. It’s about the size of a cell phone. And you apply these electrodes either side of your brain, and you start to stimulate the brain. Now, if you stimulate the brain during sleep, as if you’re singing in time with those deep brainwaves that we spoke about, in young, healthy adults, not only do you amplify the size of those brainwaves, in doing so, you can almost double the amount of memory benefit that you get from sleep.
The question now is can we translate that same technology into older adults and those suffering from dementia? Can we restore some healthy degree of quality sleep, and in doing so, can we salvage the memory function?
Indre Viskontas: So are there, you know, people talk now about all kinds of sedatives and sleep aids that are in pill form. Do these work, do they get you into the same stages of sleep? Do they mimic a night of healthy sleep? Do they have consequences that we should avoid? Is that a way to enhance sleep in people who are experiencing age related sleep deprivation?
Matthew Walker: Yeah. So the sleep aid industry is a multi-billion dollar industry. So 9 million people in the last month alone swallowed some kind of sleep medication. It’s frightening. The question is what do those sleep medications do? And perhaps that’s the even more frightening part. Because the answer is we don’t fully yet understand. Firstly, the oldest sleep medications, they were called the sedative hypnotics– nobody was going to argue that when you took those drugs, that you were awake. You definitely weren’t awake. But based on the name, you can already understand what they did. They would sedate you. Sedation is not sleep. It’s fundamentally different. And you don’t get the, the same physiological benefits that you get.
Even the newer sleep medications, however, do not seem to produce what we would think of as naturalistic sleep. So yes, you sleep for longer, or I should actually say technically, yes, you are not awake for eight hours, would be the best way I could describe it physiologically. But if you look at the electrical signature of sleep, like a fingerprint, and everyone has, you can produce these fingerprint graphs of your sleep, that medicated sleep that you get is not the same electrically as naturalistic sleep.
And because millions of people are taking these medications, we need to know what the effects are. Is it that those sleeping medications enhance your memory like natural sleep does? That would be great. Or are actually they reversing the benefit of memory? Because no drug company wants on their label, you’re going to sleep soundly for eight hours, but you won’t remember anything of yesterday.
And what’s interesting is that I only know of one study that’s really tried to examine this and we need more, and there’s a tension between probably the pharmaceutical companies and national institutes of health to fund this work. And I understand that, but there was a study done in developing animals. This was a study done from University of Pennsylvania. And they were looking at how these animals would learn during the day during sleep, sleep would delightfully enhance the rewiring of the brain. It’s like the hitting of the safe button on those memories. And there are physical changes within the brain that happen to score that memory trace even more strongly into the brain and sleep does that work of strengthening the memory trace.
But when these animals were given a drug called Zolpidem, which is more commonly known as Ambien, not only did you fail to get the rewiring benefit of sleep, you lost about 50% of the rewiring that had happened. And that worries me because if you look at the prescription age for sleep medications, it’s coming down. When are we going to get the stage, to the stage, sorry, that the age range is starting to infiltrate our educational populations. It actually worries me greatly.
Indre Viskontas: You know, it seems that some of these sleep aids are addictive, right? Is that true? That if you start taking one of these aids, then you will have trouble falling asleep without them later on?
Matthew Walker: When you come off those drugs, you have a rebound effect it’s called the rebound insomnia effect. So right now medicine will only, or let me sort of say that you should only be on those sleep medications for a short term period of time. They are only there for acute phases of insomnia. They are not recommended by the board of medicine for chronic long-term use. And you don’t need to use those sleep medications, it turns out necessarily, because we actually have wonderful behavioral ways to modify your sleep. There is something called cognitive behavioral therapy for insomnia. It’s called CBT I little, I, like your iPhone caps, CBT cognitive behavioral therapy for insomnia. And it’s a great behavioral technique. It has just as much efficacious benefit at improving your sleep during the time that you’re having the therapy, as you would have if you were taking the medications. But the great thing is that when you stop that therapy, the benefit to your sleep continuous, unlike the medication. So we’re really now starting to develop alternatives to medication.
I’m not trying to suggest that all sleep medications in all circumstances are bad, that that’s not the case. They have their time and place, but that you should be on them chronically, in a long-term fashion, is clearly not the accepted myth.
Indre Viskontas: Well, I think it’s about time for us to open up the questions to the audience. And as they’re getting that ready, I just want to ask you a really quick question. Why is it that when people get abducted by aliens, it’s when they’re sleeping?
Matthew Walker: So in addition to, so there are two wacky questions that it turns out I always have an answer for. Firstly, I will do it pro bono dream interpretation, if anyone would like to give me that. The second one is that I will explain alien abductions. When you go into rapid eye movement sleep, which is dream sleep, your brain will paralyze your body. And it’s an evolutionary adaptive mechanism. Your brain locks your body in this prison of paralysis. So your mind can dream safely. So you don’t act out your dreams. Occasionally when you’re waking up out of dream sleep, normally that prison of paralysis is released. And as you gain consciousness, you gain your ability for voluntary movement. Every now and again, the brain gets to switch off the paralysis. So you start to become consciously aware of your surroundings, but you can’t move. You can’t speak, you can’t talk, you can’t lift your eyelids, voluntary muscles. It’s often associated with a sense of dread, a sense of someone being there in the room. It’s a very frightening experience. And it accurately explains most all alien abductions. When was the last time that you heard of someone being abducted by aliens in the middle of the day? You know, nobody is sitting there at sort of the boardroom again, and it’s the middle of the afternoon. You hear the sound, you know, what was that? Well, I think Jimmy was just abducted by aliens. Did everyone see that? No. It never happens like that. It’s it’s at night, you’re in bed, you describe a presence in the room. You say that they injected you with some paralyzing agents, so you couldn’t fight back. It’s simply sleep paralysis that’s not being released.
City Arts & Lectures: This first question is going to come from the back and center of the orchestra.
Audience Member 1: You both mentioned a little bit about babies and how as infants, they have a different sleep pattern than children and teens and adults and as we get older. So I have a few people in my life who just had twins and another one who’s having a newborn, and they’re worried about their sleep quality because the babies are gonna wake up in the middle of the night and wake them up. So. Usually the response is to, like you said, teach the baby how to go to sleep. I wonder what is your, what are your thoughts on the other recommendation, which is to fall asleep when your baby does?
Matthew Walker: So if that’s a possibility, then you should certainly take advantage of that. It’s a time when sleep is desperately fragmented throughout both the day and the night. And at that moment, sleep becomes less about something you can architect yourself, regarding the clock face, and instead something that is opportunistic. So really, I would try to recommend people, if you have the ability to use shift systems, if you have another caregiver the re think about that so there is equity, so that each person gets the right amount of opportunity sleep. I know that nursing sometimes makes that equity not quite possible, but at that stage, going into perhaps this biphasic like sleep pattern where if you’re only able to get maybe five hours of solid sleep at night, thinking about that siesta like behavior in the afternoon is certainly a good idea. We do understand that getting that seven to eight hours of sleep, certainly more on the side of eight hours is important. But how you get that perhaps in this biphasic like manner is just fine. So it’s not necessarily detrimental to get that sleep in those two phases. So if it’s possible, I would recommend it.
City Arts & Lectures: This next question comes from your right in orchestra.
Audience Member 2: Thank you. So I understand the importance of sleep and maybe the evolutionary basis of sleep, why humans need eight hours of sleep, perhaps because they need 16 hours to be awake, to prove their fitness and reproduce and eat and all of those great things. And maybe bats only need four hours. So my question is why do we wake? We’ve talked a lot about sleep tonight. Why do we wake up? And in my own personal case, why at the age of 47, do I wake up at the same time every morning, whether I’ve had eight hours of sleep or two hours of sleep, whereas my teenager perhaps can sleep 20 hours if I let him.
Matthew Walker: Yeah. So, so let me just make sure I understand the question. So the question is not necessarily, why are we awake, from evolutionary perspective, but instead, why is it that I wake up at a specific moment in time? Is it’s that latter question, correct? Yeah. So there are two forces that will determine when you want to be awake and when you want to be asleep. The first force we’ve spoken a little bit about, which is your 24 hour biological rhythm, it’s called your circadian rhythm. And that rhythm is just going up and down every 24 hours, no matter whether you’re awake or you’re asleep. When it’s on its downward shift, which for us human beings, when we like to be awake during the day, it’s downward shift happens at night. So your biological rhythm is one of the two factors that likes you to be going into sleep at night, and starts to rise back up in the early morning hours and will promote wakefulness and the moment of awakening at the beginning of the day.
The second of those two factors though, is a chemical called adenosine. From the moment everyone woke up this morning, a chemical, this chemical adenosine, started to be released by the cells within your brain. The more adenosine that builds up in your brain, the more you want to go to sleep. And after about 16 hours of buildup in adults, that generates what we call a sleep pressure, and such a sleep pressure that you can’t stay awake any longer. Those two forces are usually beautifully aligned. That your biological 24 hour rhythm is on its awesome downswing– I rarely use the word awesome because it’s overused, but it truly is awesome from a biological perspective, I am in awe of your biological rhythm. It’s awesome. And at that moment, just as it’s on it’s downswing, your levels of adenosine, this sleep pressure chemical, the second fact, it is now in highest concentrations. So when those two things are most distanced from each other, your biological rhythm is ramping down, and your adenosine levels are at the highest point, that’s the moment when there is an insatiable appetite to sleep.
But let’s move it through then, through the next eight hours. As you’re asleep, the brain starts to remove all of that adenosine and it removes that sleep pressure. It’s like releasing the valve and that steam of sleep pressure goes away. After about eight hours, it’s removed all of that adenosine. So now the sleep pressure is very low. There’s not much trying to keep you asleep. And your biological rhythm is now delightfully on it awesome upswing. And so when those two things come closest together is the moment that you will want to wake up naturally. By the way, you can mess with that adenosine signal. You can manipulate it. You may have heard of another chemical called caffeine. Caffeine, it’s no surprise that it sounds similar to adenosine. Caffeine comes into your system and it latches on to the receptors, the welcome sites in the brain, of adenosine and it battles with them. And it pushes out the adenosine. It jumps onto those receptors and blocks the adenosine signal. So now let’s say it’s hour 14 and you’re starting to feel sleepy. You drink some caffeine, the caffeine now fools your brain into thinking that there is nowhere near as much adenosine around in the brain. There is, but you go back to thinking, Oh, maybe I’ve only been awake for seven hours.
The problem is that after that caffeine has been removed from your system, don’t forget that adenosine has not gone anywhere. It’s still been building up over the past two hours that you’ve been infused with caffeine. So not only do you go back to where you were two hours ago, you go back to that point, plus all of the additional adenosine that’s built up over the last two hours, and you have what’s called a caffeine crash. So I hope that explains how the, sort of the biology through these two factors helps you go to sleep and helps you wake up in the morning.
Indre Viskontas: But what happens? I mean, you know, my baby gets up most mornings at five 30 in the morning, and then the one day that he sleeps until six 45, I’m up at five 30, expecting him. Why can’t I just sleep through, if you know, I haven’t had that eight hour time period to wash away all the adenosine.
Matthew Walker: And it’s probably from an evolutionary perspective that, you know, if you were to think about how long human beings really were living, if you roll back the clock, you know, several hundred thousand years now, our life expectancy wasn’t probably much past 30 to 40. So at some point it’s almost as though, you know, your discarded goods from the evolutionary stage at that point, the focus should be on the next generation and promoting their sleep. And your role is to be awake and making sure that that next generation makes it through. That you lose sleep, you know, is– what I should say that by the way, in coming back to the aging story, so I don’t forget. Yes, as we get older, our sleep gets worse and we do get less sleep overall. We now know, however that that’s not because older adults need less sleep. That’s a fallacy. They need just as much sleep. It’s simply that the brain unfortunately cannot generate the sleep that they need. So don’t be fooled into thinking that, you know, as I get older, well, I just need less sleep. Not true.
Indre Viskontas: But why is it that as you get older, it becomes harder to sleep through those mornings when you’re sleep deprived. Is that, is that the same reason, is that those brain regions have deteriorated and aren’t functioning as well?
Matthew Walker: Yeah. So it’s probably for at least two reasons, firstly, the strength of that 24 hour biological clock, the strength of that drummed rhythmic signal, is actually weaker. So if you were to think about these sort of peaks and troughs of your biological rhythm, those mountain peaks are now at a much lower latitude as we get sorry– latitude, what am I talking about? Altitude. So the, there is a diminution in your biological rhythm that makes it harder to be fully awake during the day and truly asleep at night.
The second thing, however, is that the deep sleep generating centers of the brain are also the centers that show the earliest degeneration in aging. Unfortunately.
City Arts & Lectures: This question is from your left and the orchestra.
Audience Member 3: Hi, I’m just wondering about the role of melatonin and what it, how it affects sleep and what happens when people take melatonin pills, which I know is fairly common.
Matthew Walker: So melatonin is a hormone it’s naturally occurring within your body. It’s often called the hormone of darkness. Not because it’s sort of sinister. It’s also sometimes called the vampire hormone. Not because it makes you look longingly at people’s neck lines. It’s simply because it comes out at night. The way that your brain communicates to all of the cells in the rest of the brain and all of your body, is to release melatonin. Melatonin is the chemical bullhorn that shouts to your brain and body, it is nighttime. So melatonin is a great way to synchronize and tell your brain now is the time to sleep. And it’s the reason that it’s very helpful if you go through time zones. And let’s say I fly back home to England it’s an eight hour time zone. Now my biological clock is completely mismatched to the London time clock in itself. I can use melatonin to help fool my brain into thinking that it’s nighttime when it wouldn’t otherwise be registering nighttime. Cause my melatonin peak.
So right now all of us, as long as we’ve been in this time zone, in about four or five hours, your melatonin levels are going to peak and it’s going to help tell your brain and body it’s time to sleep. But if I fly to England, which is eight hours ahead in time, now when it’s nighttime in England, it’s still eight hours behind. It’s still, you know, the middle of the afternoon in California. So my brain isn’t yet receiving a melatonin signal. My melatonin spike is eight hours back in time. But I can take a melatonin pill, and fool my brain into thinking, Oh my goodness, we completely misjudged it. It’s nighttime. Let’s get to sleep.
But melatonin doesn’t seem to be a particularly effective sleep medication once you’re stabilized within a time zone. Now that’s not to say that melatonin isn’t potentially useful. What I mean is that relative to placebo, melatonin doesn’t seem to perform above and beyond placebo, once you’ve stabilized in a time zone. But I think the placebo effect is fantastic. It is the most reliable effect in all of pharmacology. Now we may laugh, but notice what that tells us. It tells us there is such a thing as mind over matter. If you just fool your brain into thinking that it’s getting treated, it will treat itself. That’s what the placebo effect tells you. And there is now a raft of neuroscience that is actively pursuing the placebo effect. There’s the clue to self healing. It’s been staring us in the face for 40 years of neuropharmacology. So. If you think a sleep aid is working for you, whether or not scientists tell you that it’s working, if it does seem to give you a benefit, keep taking it.
Indre Viskontas: But the melatonin pills that we take are not regulated by the FDA.
Matthew Walker: That is a problem.
Indre Viskontas: And does it, if you ingest it orally, does it cross the physical barrier between your bloodstream and your brain, the blood brain barrier?
Matthew Walker: Yeah, it seems to be unclear that melatonin can actually get into the brain. There is a protective barrier around your brain that will only let some substances in there, and that barrier does seem to actually prevent sort of orally administered melatonin. The studies are that there is some potential effects depending on the compound. But yeah, that’s one of the challenges that we would face, even if melatonin did seem to be efficacious.
Audience Member 4: Thank you, Matt, great stuff. And also thank you for answering questions. My question to you is could you be kind enough to comment on chronotype, the larks and the owls, and also the stigmatization of the owls, because I’m one of them.
Matthew Walker: Yes. So chronotype is simply your preference for morningness versus eveningness. And we describe those as larks and owls: owls like to stay up late, wake up late , larks to sort of go to bed early and wake up early. And society has principally been designed around the larks and is very much designed against the owls, with real health implications for folks like yourself. What’s causing that? It turns out that a lot of it is due to genetics. There are genes that will determine your chronotype, whether you prefer mornings, whether you prefer evenings, in terms of optimal time periods. So we understand the biology behind it.
What’s interesting by the way, is that even though you are genetically defined as an owl or a lark from conception, of course, your, your sweet spot of morningness and eveningness changes across the lifespan. So, you know, when you’re a child, even though you wanted to stay awake late, you know, you couldn’t really, so you’d be going to bed early and you’d wake up early much to the annoyance of your parents. Then once you hit those teenage years, now, you’d like to go to bed later and wake up later. And then as you progress into adulthood, that shift is dragged back again. And now you start to sort of find your overall sweet spot based on that, those genetics.
You could then ask the question, well, why? Why has Mother Nature programmed variability? Wouldn’t it make sense for us as a social species to all be synchronized, to all be waking up at the same time and going to sleep at the same time? Why have that variability? Now? We don’t know, but my theory is this: as I mentioned, you are so vulnerable when you’re asleep. And if you’re getting your eight hours, you’re vulnerable for eight hours, that’s an immense amount of time. What we know from studies of those cultures untouched by electricity is that they co-sleep, they don’t all go away to sleep by themselves in a little room. They sleep together with family, other friends. Imagine now the scenario, if you’re a co-sleeping community. Now it starts to make a lot of evolutionary sense. Some people are naturally going to want to go to bed late. Let’s say 2:00 AM in the morning. And then there are other people who are going to want to wake up, having gone to bed at 9:00 PM, at 5:00 AM in the morning, or 6:00 AM in the morning. So now as a collective species, it’s a little bit like the birds. Now there’s always someone awake until about 2:00 AM, and there’s always someone awake from 6:00 AM. So you are vulnerable now as a collective for only four hours, rather than eight hours. You could imagine Mother Nature would never turn away from the opportunity of gaining 50% increased survival fitness, which is the difference between four hours of vulnerability versus eight hours of vulnerability.
Indre Viskontas: One last thing I wanted to ask you, and that is, what keeps you up at night in terms of your research? What do you find most exciting that you just can’t go to sleep and related to sleep research?
Matthew Walker: Well, that’s one of the ironies of, of sleep research. Firstly, you have to deprive yourself of the very thing that you’re studying by doing these sleep studies at night. And secondly, you become the Woody Allen neurotic of the sleep world. Because I know the exact biology that should happen to push me into sleep and get me into sleep. And if I’m lying there at night awake, you know, I’m now thinking, well, my dorsolateral prefrontal cortex is not shutting off. My histamine is not… and at that point you’re dead in the water for the next like two hours.
For me, I think one of the most exciting things right now is the role of sleep in psychiatry. There is, we cannot find a single psychiatric disorder where sleep is normal. Sleep, I think, has a powerful story to tell us, not only in our understanding of psychiatric illness, but also our treatment and maybe prevention of psychiatric disorders. And if you look across medicine, we’ve done wonderful work in combating things like infectious diseases, even in cancer we’ve made great progress. When it comes to the brain disorders and particularly the psychiatric disorders, we’ve made remarkably little progress. We cannot bend the curve of advance and discovery. I think sleep is going to be one of the revelations over the next decade, in terms of our understanding of serious mental health illness.
Indre Viskontas: Well, thank you for joining us in conversation Matt Walker.
City Arts & Lectures: You’ve been listening to The Science of Sleep with Matthew Walker and Indre Viskontas. This program was recorded on May 20th, 2015.