Wednesday, Nov 10, 2021 • 49min
#267 — The Kingdom of Sleep
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In this episode of the podcast, Sam Harris speaks with Matthew Walker about the nature and importance of sleep. They discuss sleep and consciousness, the stages of sleep, sleep regularity, light and temperature, the evolutionary origins of sleep, reducing sleep, the connection between poor sleep and all-cause mortality (as well as Alzheimer’s disease, diabetes, obesity, and heart disease), sleep across species, learning and memory, mental health, dreams as therapy, lucid dreaming, heart-rate variability, REM-sleep behavior disorder and parasomnias, meditation and sleep, sleep hygiene, different types of insomnia, caffeine and alcohol, sleep efficiency, bedtime restriction, cognitive-behavioral therapy, napping, sleep tracking, and other topics. SUBSCRIBE to listen to the rest of this episode and gain access to all full-length episodes of the podcast at samharris.org/subscribe http://samharris.org/subscribe Learning how to train your mind is the single greatest investment you can make in life. That’s why Sam Harris created the Waking Up http://wakingup.com/ app. From rational mindfulness practice to lessons on some of life’s most important topics, join Sam as he demystifies the practice of meditation and explores the theory behind it.
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Sam Harris
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Sam Harris
00:05
Welcome to the Making Sense podcast. This is
Sam Harris
. Just a note to say that if you're hearing this, you are not currently on our subscriber feed and we'll only be hearing the first part of this conversation in order to access full episodes of the Making Sense podcast. You'll need to subscribe at samharris. org feed.Share
00:25
You'll find our private rss feed to add to your favorite podcaster along with other subscriber only content. We don't run ads on the podcast and therefore it's made possible entirely through the support of our subscribers. So if you enjoy what we're doing here, please consider becoming one.
Share
00:47
Today. I'm speaking with
Matthew Walker
. Matt
is a professor of neuroscience and psychology at UC Berkeley
and the director of its sleep and neuroimaging lab and he's also a former professor of psychiatry at Harvard University
. He has published over 100 scientific studies and has appeared on 60 Minutes
, Nova, BBC News,
and many other outlets.Share
01:10
His first book
Why We Sleep
has been an international bestseller and he also hosts his own podcast, The Matt Walker Podcast. I've been wanting to speak to Matt
for quite some time because as you'll hear, I've been increasingly worried about the quality of my own sleep.Share
01:27
I'm late to the party here but now I'm convinced of the importance of sleeping well most nights and
Matt
and I get into all the details here about the nature and importance of sleep. We discuss sleeping consciousness, the stages of sleep, sleep regularity, light and temperature, the evolutionary origins of sleep, the generally doomed attempt to reduce one's need for sleep.Share
01:56
The connection between deficiencies and sleep and all cause mortality. Alzheimer's disease, diabetes, obesity, and heart disease, the role that sleep plays in learning and memory and mental health, heart rate variability.
Share
02:13
Rem Sleep
behavior disorder and various parasomnia as we just got to lucid dreaming dreams at a kind of therapy, the connection between meditation and sleep, the various forms of insomnia and there are practical tips for what to do about them strewn throughout our conversation. We discuss sleep hygiene, caffeine, and alcohol, sleep efficiency, bedtime restriction, napping, and finally sleep tracking.Share
02:45
And as you hear on that final topic of sleep tracking
Matt
and I discover that each of us is associated with the company aura that makes a sleep tracking ring. I am a minor investor in the company and Matt
is its scientific advisor. Neither of us knew about the connection before we started talking and you'll hear I have a bit of a love hate relationship with my own or a ring.Share
03:08
It is a remarkable device, but I may have what
Matt
calls or ethos Omnia, which is an overabundance of concern about my sleep data in any case. Make of that. What you will. I hope you find this conversation useful as it runs nearly four hours and now I bring you Matthew Walker
.Share
03:31
I am here with
Matthew Walker
. Matt. Thanks for joining me.Share
Matthew Walker
03:37
It's a delight in a privilege to be speaking with you,
Sam
thanks for having me.Share
Sam Harris
03:42
So you've written a book
Why We Sleep
. That seems to have gotten into the hands, if not the brains of more or less everyone. And now you have a your own podcast, the Matt Walker podcast and you have been on many, many podcasts that I've noticed talking about the science of sleep and seemingly almost single-handedly making people newly aware of the importance of sleep in their lives, both from a side of, you know, physical health and mental health, emotional regulation.Share
04:22
Really just across the board when you're talking about human well being, the difference between good and bad sleep seems paramount and I must say I have really neglected sleep as a variable for most of my life. In fact, I think I was early in life toyed with the fairly crazy ideal of limiting sleep so as to boost productivity and we'll get into all of that.
Share
04:51
But before we dive into the specific chapters of our conversation here, perhaps you can introduce yourself, your, your background intellectually and academically and just tell us how you came to focus on sleep.
Share
Matthew Walker
05:06
I wish I could take the compliment of bringing sleep back onto the public awareness map. I stand on the shoulders of many of my colleagues and they are astronomically wonderful. So I try to do my part.
Share
05:20
In terms of my background, I am a professor of neuroscience and Psychology at
the University of California Berkeley
in America
And I've really tried to dedicate myself to understanding the question of Why We Sleep
for the past 20 years. I think like most people, I am an accidental sleep researcher.Share
05:44
I often think when kids are young and the teacher says, tell me what you would like to be when you grow up, no one's shooting their hand up in the classroom and saying I desperately want to be a sleep-researcher and...
Share
Sam Harris
05:59
I can attest that when I started my neuroscience Ph. D. someone from a sleep lab, I forget who tried to recruit me to their lab. And I I thought why would I want to study sleep? I had no interest at that point. And you know now uh feel some chagrin over that dismissal because it is increasingly fascinating and as I said, consequential.
Share
Matthew Walker
06:24
And in some ways I, you know, I don't blame you. Maybe at the time, certainly even 20 years ago, one could argue it's almost academic suicide to suggest that you want to become a sleep researcher. And not necessarily truthful, but some would argue that it was almost a charlotte in science, to begin with.
Share
06:43
And of course it is, it's the most bizarre, strange, illogical, irrational from an evolutionary perspective, idiotic thing that an organism can do and you're going to leverage an entire academic career on that platform.
Share
06:59
Good luck and good night would be the I think the tagline, but I was studying for my Ph. D. people with different forms of dementia and I was using brain wave patterns to try and differential diagnose them very early on in the course of dementia and I was failing miserably couldn't get any good results. And one weekend I had this little igloo of journals that I would retreat to which tells you everything about my social life.
Share
07:27
And I started to learn that some of those dimensions would eat away at sleep centers and other forms of the dementia as would not because there are many different forms of dementia. So I realized I was measuring my patients at the wrong time which was when they were awake and I should be measuring them when they were asleep.
Share
07:44
I started doing that. I got some fantastic results. And at that point I started to ask the question, I wonder if these sleep disruptions and impairments are not a consequence of the dementia is not a symptom of the department dementia. Maybe they are a cause of the dementia.
Share
08:04
But I realized 20 years ago, no one could answer a very fundamental question, which was why do we sleep? And I think the crass answer at that time was that we sleep to cure sleepiness, which is the the fatuous equivalent of saying I eat to cure hunger, tells you nothing about the unique benefits.
Share
08:25
But then I started to explore this thing called sleep and I fell absolutely in love with it. And to this day, 20 years on I still think it is the most beguiling thing in science. It is a lover for that's not left me for all of those decades and I remain an amorous partner. Two. It's wonderful gifts both nightly as a practice and also from a intellectual and academic and research perspective. Does that give some background?
Share
Sam Harris
08:56
Yeah, yeah. If I can follow your romantic analogy here, sleep is a a fairly coy mistress for many of us and this, you know, speaking personally, this is always and not even on the back burner for me as a problem to solve in my life. I just I've accustomed myself to sleeping badly and just accepting on some level that I I sleep badly.
Share
09:26
And so encountering your work is fairly arresting to someone in my condition because the stakes as we will elucidate here are incredibly high given the connection between sleep and health. So I wanted at the outset, address the component of worry, your worry about sleep because many people listening to us, we'll also recognize in themselves that their their sleep is far from ideal. And to add a layer of worry too, that is obviously counterproductive when the goal is to make it easier to sleep soundly and on some better schedule in general.
Share
10:12
So, can you address this this effect that our conversation is likely to have, especially when we're talking about possible links between poor sleep and dementia and you know, all the rest. It's just it's very easy to begin to treat this as some kind of a medical emergency in the offing. What do you have to say as a by way of guidance or caution on that point?
Share
Matthew Walker
10:38
In some ways it's a rock and a hard place that I found myself in. And this is something that I've learned since publishing the book. And I think it's something that I've corrected in my communication to the public as I was writing the book at the time, at least within the public sphere. As you mentioned, sleep was the neglected step system in the health conversation of today and it was that way.
Share
11:02
And I was so familiar as all of my colleagues were with the disease and the sickness and the suffering that was happening because of this sleep deficiency that was so pernicious throughout most First World nations that I wanted to try to - no pun intended for either this podcast or the topic - but sort of wake people up to the fact of the importance of sleep.
Share
11:29
And I think that in my communications and maybe even in segments of the book, I was perhaps heavy handed and I had neglected to recognize the concern for the sleep anxious and those who are having sleep difficulty. And I've since become so much more sensitive to that. And I can't deny the science.
Share
11:54
I can't not tell you about the links between insufficient sleep and alzheimer's disease, obesity, diabetes, cardiovascular disease, depression, anxiety, even suicide, some forms of cancer. But I also don't want people to become overly anxious. But how do you do that? How do you find that sweet spot? And so for me, it's been a real lesson and a lesson.
Share
12:23
Also because I am no poster child for sleep, I have had my battles and I did not mention them in the book and I think I should have being personally open. I'm a very private person. I've had at least three bouts of insomnia during my lifetime and they were vicious. And just because you know a little about sleep doesn't mean as though you are immune to its vagaries it is a mistress. That can be very fickle.
Share
12:51
So I think for this podcast it's important to keep in mind two things first, everyone has a bad night of sleep. And if you're there at night struggling to fall asleep, don't worry. Even with all of the facts and the science that we will discuss, it's not the worst thing in the world.
Share
13:13
The second thing is that if you are persistently and continuously chronically struggling to sleep, you don't have to because there are efficacious treatments, many of them non-pharmacological, which is great that can help course correct. In fact, even in older adults where you think there is no hope at all for a solid night of sleep.
Share
13:35
Those therapies, many of them seem to be beneficial to restoring some degree of good sleep. So you don't have to suffer in the nighttime silence. That there is benefit though. I think that that's perhaps the best way to approach it with sensitivity, compassion understanding, but truthfulness to the science.
Share
13:57
You know, I wouldn't want to make people nervous about you know, eating so precisely that it doesn't change their blood sugars. Set them on a path towards pre diabetes or type two diabetes. And where you become so obsessive and anxious that food and the joy and pleasures of eating start to fail.
Share
14:20
I also don't want to do that with sleep, but I equally don't want to tell you that it's fine just to eat a pint of ice cream every night and that your blood sugar won't suffer. I'll tell you about that science too.
Share
Sam Harris
14:31
Yeah, well, so that's great by way of introduction and we will get into all of the aspects here, including all of the practical recommendations you have for improving sleep and bypassing any perverse cul de sac of worry about sleep that can get in the way of that project. So let's just begin, let's jump into our first chapter here on what sleep is. Even before answering the question is the title of your book about
Why We Sleep
. What is sleep?Share
Matthew Walker
15:05
From a functional perspective. I think the headline statement you could argue is that sleep physiologically at least is perhaps the single most effective thing that we can do every day to reset the health of our brain and our body and that's not to dismiss food or nutrition or exercise.
Share
15:24
But if you were to... take you
Sam Harris
and I were to deprive you of food for 24 hours, deprive you of water for 24 hours. Deprive you of physical activity for 24 hours. Or deprive you of sleep for 24 hours. And I were to look across your brain and your body and see which one demonstrates the more demonstrable empowerment.Share
15:44
By a very large margin, it's it's sleep, but I don't want to sort of do that coke, Pepsi dr pepper, I'm still missing one. I can't think of it challenge. So you could ask from a functional perspective what sleep is. You can also ask what is sleep as a process that unfolds across the night in terms of its architecture. And then you can also ask and debate what is sleep as a conscious state versus a non-conscious state.
Share
16:15
And so I'm happy to maybe speak about how sleep unfolds since that may be the logical entry point or just go straight into how we can noodle and wrestle with the idea of it being a conscious versus non-conscious state, which can get us into total logical waters, but you tell me which of those two perhaps would be best to start with or fruitful for you.
Share
Sam Harris
16:35
Yeah. Well, the question of whether it's conscious is I know I've spoken about this elsewhere, it's very difficult to resolve just because it's difficult to discriminate an interruption in consciousness from a mere failure of memory.
Share
16:52
So for instance, dreams are routinely conscious, but it's also possible to have dreams and not recall them at all. And then one could wonder whether those dreams, you know, whether those stages of
Rem Sleep
are actually associated with conscious dreaming. And one could wonder that the state of deep sleep is also a state of conscious enjoyment of something quite formless and profound, but there's just no memory of it.Share
17:21
And so we read it as just a loss of experience for that period. So I don't know how we would I'm happy to hear anything you think on that topic, but I'm unaware of anything that would resolve that for us.
Share
Matthew Walker
17:34
I think it's a very elegant point which is we rely for that question in part subjectively from the sleeper themselves. A report of whether or not they were experiencing anything going through their mind just before we woke them up and said, what were you having as an experience? And that suffers from the failures of memory which we know happened just because you don't remember your dreams doesn't mean that you weren't dreaming.
Share
18:04
I think one way that you can get closer, but we will still fail is to split that question apart on the basis of perception, which is to say depending on your... I mean behaviorally the way that we define sleep in other species where we can't, for example, stick electrodes on them is as a condition in which the organism stops responding to the outside world, which is about perception.
Share
18:32
Does this mean that we are not conscious during sleep, because we typically stop responding to the outside world in all stages of sleep? And that depends on your definition of consciousness.
Share
18:43
But we stop interacting with and for the most part perceiving the outside world, which some would argue is a loss of consciousness or at least a shift towards non-consciousness. But I'd counter-argue that we don't entirely stop perceiving the outside world. So, for example, I can have electrodes on your head and I can place sounds while you're asleep that don't wake you up.
Share
19:09
And I can still see that the brain at some level is processing those sounds in a way that is not dissimilar to the way it does when we're awake, consciously perceiving those sounds. We can do
FMRI
studies and we can play those sounds as you're sleeping in the MRI
scanner. It's hard to believe that people can, but they do sleep in the scanner.Share
19:30
And you can see that there are different ways of perception. There's a great study that looked at new mothers and what they found was that when they played the cry of their infant versus another sound even though they remained asleep, there was a very different networks salience network activated in response to the child of that mother versus another sound of equal volume etcetera.
Share
19:56
So there's definitely some degree of processing and discriminatory processing, but I still don't think it's the same non-conscious state as anesthesia, meaning that there is still some degree of perception of the outside world during deep sleep. In other words, what we call extra section, the ability to focus or sense the outside world.
Share
Sam Harris
20:18
Well, there's got to be just based on the fact that you can wake somebody up from deep sleep. So that's got to get in somehow.
Share
Matthew Walker
20:26
That's exactly it. Yeah, I think you exactly predicted where that conversation was going. Which is that no matter what stage you're in sleep at least as a condition in which it is environmentally reversible. For example, if a sound is loud enough or if someone were to pinch your skin hard enough, which would you would be a desperately cruel thing I'd need to do when someone's asleep.
Share
20:49
You would wake up from sleep, which is to say that in sleep we are unresponsive, but that state of unresponsive Itty is reversible. Now that's not true of anesthesia or death for as best we can tell. So I think it's very hard to argue then that we don't have a very substantive yet qualitatively different form of consciousness when we dream, especially during when we go into
Rem Sleep
dreaming.Share
21:14
So I think we can get a little bit closer to a dissection of what do we think of as the state of conscious processing during sleep? But I still feel as though I don't see data that can really solidly give us one argument in either favor conscious non-conscious state.
Share
Sam Harris
21:34
Yeah, I would just add here that conversely there are states of meditation or drug intoxication where someone is also totally unresponsive to the outside world, but all too conscious of something right? I mean in terms of their subjective report once they come back from those experiences. So there's kind of a double dissociation here.
Share
21:58
So I think responsiveness to stimuli isn't the cut we need. We need... we obviously need the neural correlate of consciousness where we can just scan your brain and say buy some methodology and say "Okay, this is the footprint of consciousness in the human brain", and it winks out in this condition, let's say general anesthesia and it's attenuated to this degree in this stage of sleep. But unfortunately we don't have that yet. And I think there are conceptual and operational limits to our getting it.
Share
22:32
Again, the role of self report is always potentially confounding and seditious here because you can just you know, we just need a sufficient cohort of people who are reporting things that occurred in the chapter that we're deeming to be unconscious and you know, either we're going to think they're delusional or they're lying or they're in some other way wrong or we're going to or that's going to erode our confidence that really the lights are out during that epic.
Share
Matthew Walker
23:06
I think self report speaking about fickle mistresses.
Share
Sam Harris
23:09
Yes, yeah.
Share
Matthew Walker
23:11
Yeah. It's so prone to all of those errors.
Share
Sam Harris
23:13
Okay, so with that caveat in mind, let's launch into it would be good to just give us the structure of sleep here in human beings. You can say anything else you want about other animals. But what is sleep for people?
Share
Matthew Walker
23:29
Sleep at least in human beings... And in fact, in all mammalian species, as long as they are land-dwelling as a caveat, there too is broadly separated into two main types. On the one hand, we have
Non-Rapid-eye
Movement Sleep
or Non-Rem Sleep
for short.Share
23:47
And on the other hand, we have
Rapid Eye Movement Sleep
or Rem Sleep
often want to make people clear on the fact that that's named not after the popular 1990s Michael Stipe
pop band, but because of these bizarre horizontal shuttling movements that occur during the stage of sleep, that's where it gets its definitional name from. And coming back to Non-Rem Sleep
, which I always feel sorry for, by the way, isn't it?Share
24:17
Isn't it sad to be defined by something that you're not, you are not
Rem Sleep
in this case your deep and light. That's correct. So Non-Rem Sleep
is then further subdivided into four separate stages increasing in their depth of sleep.Share
24:37
So stages one and two, or what we would consider or your sleep tracker will probably try to tell you are the light stages of
Non-Rem Sleep
, whereas stages three and four, that's the really deep Non-Rem Sleep
and Rem Sleep
then is the stage in which we principally dream.Share
24:57
Depending on your definition, dreaming isn't exclusive to
Rem Sleep
, but for what most people would say in the lay public, this is dreaming, what they're really referring to are the bizarre narrative, hallucinogenic emotional memory-laden experiences that come from this thing called Rem Sleep
.Share
25:20
So those two types of sleep, Non-Rem and Rem will play out effectively in a battle for brain domination throughout the night and that cerebral war between non rem and rem in humans at least. And it's different for different species will last about 90 minutes and that creates a for the average adult, a prototypical 90-minute cycle where you go into
Non-Rem Sleep
and then you go into Rem Sleep
.Share
25:49
But what changes, however is the ratio of non rem two rem within those 90 minute cycles as you move across the night. So in other words, in the first half of the night, the majority of those 90-minute cycles are going to be comprised of lots of
Non-Rem Sleep
, particularly deep Non-Rem Sleep
. But as you push through to the second half of the night, that sort of seesaw balance shifts over and those 90-minute cycles are comprised of much more Rapid-eye Movement Sleep
and very little deep sleep.Share
26:26
And that has some consequences that we can also talk about. But I would probably mention also every one of those stages of sleep or almost all of those stages of sleep we have now learned are important. There is no one more important stage of sleep than the other. Now you can argue.
Share
26:48
Well what are you talking about importance? You're talking about mortality, risk and death and we can use that as a filter to debate that as well. But overall different stages of sleep provide different functions for the brain and the body at different times of night. So we need all of those stages.
Share
Sam Harris
27:06
And is it true that we generally wake up however briefly and In discernibly after each of these 90-minute phases you get through your rim period, and then there's a brief awakening?
Share
Matthew Walker
27:20
That's that's absolutely you definitely need to be a sleep researcher, take a sabbatical and...
Share
Sam Harris
27:25
Build me a time machine and I'll go back to the conversation differently.
Share
Matthew Walker
27:30
So we do know that usually at the end of every one of those 90-minutes sleep cycles at the end of each of those rem phases.
Share
27:40
There is a brief termination of sleep where we wake up and in part we think that that's perhaps because of the the need to maneuver the body and change the body's position. So we have these brief awakenings, they're usually so brief that most of us don't recall them. They're not imprinted in memory, but everyone will typically have a brief awakening and then a movement episode after where they shift position.
Share
Sam Harris
28:07
Right. And we'll talk about sleep tracking and the tools that are available to do that personally beyond going into a sleep lab and getting totally hooked up. But viewing these stages in their totality, you've said that each is indispensable but it does seem at least in the way one communicates the imperative to get all of these stages. Most of us are not deficient in the stages of light sleep.
Share
28:40
And it's really the stages of rem and deep sleep that are marketed as truly restorative, right? And then those are the areas of real deficiency. So for instance, if someone was sleeping six hours but they got very long epics of deep sleep and
Rem Sleep
, would that strike you as a much healthier profile than someone sleeping six hours, But it's mostly devoted to the stages one and two of light sleep?Share
Matthew Walker
29:12
Yes, I think that that's for to say we do need stage two as well. We've discovered that Stage two,
Non-Rem Sleep,
is associated with certain forms of memory and memory processing.Share
29:24
And There is a particular electrical feature of stage two
Non-Rem Sleep
which continues on into deep Non-Rem Sleep
, stages three and four called sleep spindles, which are these beautiful little champagne cork synchronous bursts of electrical activity that happened during Stage two Non-Rem Sleep
and then stages three and four.Share
29:47
They last for about a second in a second and a half. And they seem to be critical for a number of different processes of both the brain and they seem to transact or be at least associated with several benefits for the body. But overall, I would say that it's very difficult to have a night where you're not transitioning because when you go down into deep
Non-Rem Sleep
, you have to progress through Stage two.Share
30:13
And when you're coming out of deep
Non-Rem Sleep
, you have to progress through Stage two Non-Rem Sleep
. Again, the lighter form of Non-Rem Sleep
before you get up into Rem Sleep
.Share
30:23
And so it would probably be rather difficulty... you can manipulate conditions in which this can happen, which I won't bore you with, but where you could have the scenario that you described, but for the most part, you're still going to get that stage two
Non-Rem Sleep
. Yet, what you said is correct.Share
Sam Harris
30:42
Well, this is where I'll I'll cede you with practical questions throughout. But the first comes to mind here is what are the implications of waking with an alarm clock versus waking with a change in lighting conditions born of sunlight coming through the window? I guess there's the implication of you of using a sleep mask or a or blackout curtains where you're not getting those environmental light cues.
Share
31:13
Yeah, I can imagine, you know, if you're unlucky your alarm clock rings when you're in in stage four sleep, say, and you're brought out of that are, you know, less than ideal way? What are those, what are those effects? And what do you actually recommend if a person's schedule allows for it? What what do you recommend as a mode of of waking up in the morning?
Share
Matthew Walker
31:36
Unless you are waking up within the first couple of hours of sleep, it's unlikely that your alarm would wake you up in the deep stages of
Non-Rem Sleep
. That's not true, however, if you take an afternoon nap and that nap lasts a little bit too long and by too long, what I mean is you're going past that sort of 20 to 25 minutes and you're starting to go down into the deep sleep. And then your alarm wakes you up, then you almost have this kind of sleep hangover for the next hour or so.Share
Sam Harris
32:10
Those naps are terrible. Yeah, it's with a change of time zone when you're when you have terrible jet lag and you decide "Okay, there's no way I'm going to make it to the evening, so I gotta I'm gonna give myself an hour to sleep here", and that waking up from that hour is just about the worst wake up one ever gets.
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Matthew Walker
32:29
It's pretty grim, isn't it? And it's what we call sleep inertia where you get a state carry over where your brain never typically wakes up from is jolted out of that deep sleep, naturalistically from an evolutionary perspective across millions of years, That's not been the case. And so were not well prepared for recovering from that assault and therefore we suffer this terrible sleep inertia so it's not so likely to happen, but when it does happen, it's grim.
Share
32:60
It can also happen at night when for example, you get a phone call and all of a sudden it wakes you up at 2: 30 or 1: 30 in the morning and once again you're jolted out from that deep sleep and yes, you can answer the phone and you can be somewhat responsive, but it is just grim. You're in this total treacle haze of cognitive dysfunction and it's all you can do to allow words to tumble in some meaningful way, one ft in front of the other out of your mouth.
Share
33:33
So that is perhaps a less likely circumstance. What would I suggest? It's difficult because one of the critical things that people need to do to get their sleep back on track is the simple act of regularity which is going to bed and waking up at the same time, no matter whether it's the weekday or the weekend and for that we often require an alarm clock.
Share
34:01
And I also advocate for people not just to have an alarm clock in the morning, but why don't we have a to-bed alarm as well as a to-wake alarm? And it's one way to help keep us on schedule and track. I would say, however, that if you study hunter-gatherer tribes whose way of life hasn't really changed for you know, hundreds if not thousands of years, they don't seem to wake up in an artificial manner.
Share
34:28
And if you ask them, do you find ways to force yourself to wake up? They find it a perplexing question. Why would you, why would you terminate something that's not yet complete. It's a little bit like saying why would you go out to your favorite restaurant order?
Share
34:45
Your favorite dish, have two bites of that dish and then get up and walk out. You would stay until your phone when you are complete with that meal and why would we wake up when we are not yet full of the sleep that we need and mother nature will take care of that when it's time to wake up and we've had the sleep that we need. We do. So one way some people will ask me, how do I know if I'm getting enough sleep?
Share
35:11
It's not the ideal way. But one suggestion is to say if your alarm clock didn't go off in the morning, would you sleep past that alarm, and if the answer is yes, then you're still carrying some degree of asleep need, which means that by waking up artificially you're inducing a sleep debt as a consequence.
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Sam Harris
35:28
What about the role of light cues and bringing someone out of sleep?
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Matthew Walker
35:33
It's we used to think that light perhaps was the trigger of or one of the facilitating functions for rising people out from sleep in the morning. And again by looking at those hunter-gatherer tribes. What we found is that that's not really the case. They often typically will wake up a little bit before the dawn.
Share
35:56
What seems to be the trigger for the arrival of wakefulness and the termination of sleep is more so temperature, both the internal temperature and the ambient temperature rising because often they will sleep with the environment with the ambient temperature. Unlike many of us in modernity where we have a controlled temperature.
Share
36:21
And so that's not to suggest that light can't be a facilitator to help you wake up in the morning. And in fact, I will I have one of these little smart lights next to my bedside and I program it to try and say, you know, two minutes before the time that you're supposed to wake up start to bring light into the room.
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36:43
I would say though that I do have an alarm myself, my alarm is and we can get into sort of krona types and what your preferences. But my alarm is set for around 7: 04 in the morning or at 7: 04 in the morning. Not because there's anything special or unique. Please don't go rushing out and changing your wake-up time to that.
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Sam Harris
37:04
We're not going to have a chapter on numerology here?
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Matthew Walker
37:09
The reason I do that is why not just be idiosyncratic. Why would you set it, you know, 7: 05 or seven or 7: 10, but just why not? 7: 04. That tells you probably everything about me and why I'm desperately unpopular, but... So, but I usually wake up naturally. I would say about 80% of the time I wake up naturally before my alarm clock.
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37:32
So I think there are one of the worries that people have when I tell them to do the experiment, if you have the luxury and the schedule flexibility to do it, stop your along and just sleep in the way that you are, your body wants to sleep. The greatest worry is that, my goodness, I normally wake up at seven and I'll probably wake up at nine o'clock in the morning is the first concern.
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37:56
Now, that may be true to begin with for the first few days because you're probably trying to sleep back a debt that you've amassed chronically over weeks if not months or years. And the second problem is that when people sleep long, they wake up and once again they have that strange sleep hangover effect where if they get nine hours of sleep, they feel worse than when they get seven hours of sleep.
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38:20
That is typically because you are in the phase of paying back the debt. And if you let that experiment play out for another week, you wash away that sort of pressure to sleep. Now we can speak about sleep debt and whether you can ever truly pay back the bank or not, but that goes away with time. It's sort of like detoxing from a drug at first it's brutal. And you have all of these side effects and you have a withdrawal syndrome. And in some ways, that's the withdrawal syndrome where you start sleeping longer that settles down.
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38:53
It's like a shot and then it finds a sweet spot. And gradually you will actually acquiesce to your typical sleep need in your sleep profile. Most people don't have the luxury to do that. So light can be helpful. Temperature is one. I also have one of those smart home thermostats and temperature is critical for sleep. We need to ironically warm-up to cool down to fall asleep and then we need to stay cool to stay asleep and finally we need to warm up to wake up. And so you can create a bespoke tailored temperature profile for your night of sleep that can help to some degree.
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39:37
Now of course you're under the sheets and the ambient has some role to play, But it's also altered by what's going on locally underneath the sheets too, so you can't control it exquisitely. And that's where smart mattresses are coming in to try and take that out the equation.
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39:54
So those are some of the ways that you can play around with sleep. I do like the idea if you are, particularly if you are a night owl and you struggle to wake up at the time that society forces you to, which is not in synchrony with your morning nous of evening, this preference.
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40:15
You can use light in the morning, but then you can reverse that trick in the evening where you try to ensconce yourself with as much dim light and darkness to help you try to get to bed a little bit earlier. So it's not as though light should be dismissed and you know, blocking devices, blackout curtains in masks, earplugs, sound is another pollution that will disrupt your sleep.
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40:41
I will typically use all of those. I have blackout curtains. I have an eye mask, and then I have earplugs. I think I'm starting to sound like the
Woody Allen
neurotic of the sleep world, but that's just me.Share
Sam Harris
40:53
Yes, Well, all we need is one picture of this setup and to completely discredit you as an expert on sleep.
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Matthew Walker
40:58
Oh, I feel so discredited by lots of different things, but that would, I think seal the deal.
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Sam Harris
41:03
Okay, so let's transition to the question of
Why We Sleep
. I think there's probably no real boundary between what sleep is and why we do it conceptually here, at least in places. Because part of the story here is the, the evolutionary question of just why sleep is a thing, how it came to be that animals like ourselves dedicate so much of their lives to this state that seems fairly pointless and even dangerous.Share
41:36
I mean, this is the you can imagine civilization, the danger is less salient, but just imagine how precarious it would be to go out in the woods where there are bears and perhaps several other species that could consider you a meal and to uh just take eight hours of darkness to be unconscious for I guess there's a potential evolutionary answer there, in that the one thing you're not doing when you're sleeping is stumbling around in the dark where you're not very good at seeing and several other things can see you better than you can see them.
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42:17
But I'm not sure that's an adequate rationale. So let's begin talking about the origins of sleep as we know them or can hypothesis about them. What do you think about why sleep even exists?
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Matthew Walker
42:36
So far in every species that we've studied to date sleep or something that looks very much like it seems to exist and what that has suggested is that sleep evolved with life itself on this planet and has fought its way through heroically every step along the evolutionary pathway.
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Sam Harris
42:58
Let's linger on that point. That's very interesting because you can imagine the adaptive benefits that would generally accrue to any species that could just get over its need for sleep. I mean, there would have been you would think a selective pressure in the direction of completely erasing sleep. So it suggests that it's rather hard to do.
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Matthew Walker
43:20
I think it's a beautiful way of thinking about it because from an evolutionary perspective, just as you noted, it is the most idiotic of all things. Firstly when you're asleep, you're not eating, you're not foraging for food, you're not finding a mate, you're not reproducing, you're not caring for your young.
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43:37
And worst of all, as you noted, you're vulnerable to predation so on any one of those grounds, but especially all of them as a collective sleep should have been strongly selected against during the course of evolution. And it's once been said that if sleep doesn't serve an absolutely vital function, then it's the biggest mistake the evolutionary process ever made. And what we have now since learned is that mother nature didn't make a spectacular blundering, creating this thing called sleep.
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44:07
But even very old evolutionary, you know, species like earthworms, for example, seem to have periods of it's called lethargic essentially a sleep-like state. You know, this takes sleep back millions of years. Even some bacteria that seemed to live at least several days. They will have an active phase in a passive phase, perhaps the precursor to sleep. So you're right. You could well imagine why if some species had understood away to circumnavigate its way around the essential need for sleep, it would have dominated for lots of different reasons, at least within its species category.
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44:50
The fact that we haven't seen that yet argues that sleep must be fundamental at the most basic of biological levels. And it's one of the reasons why when people will say to me, well, can't you, you know, if you're a doctor training, I think we learned to overcome our need for sleep, we we learned to to tolerate and deal with insufficient sleep and you can do that if you could trust me.
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45:16
I think more than, you know, there's some degree of hubris there, which is where the nature if she could have even halved the amount of time that you are vulnerable to all of those vicissitudes of sleep. She certainly would have. And the fact that it's been preserved tells you that doesn't seem to be possible. And within the lifespan, we think that we can come along and within a 10-year training over career, we could overcome it. It's unlikely to be the case.
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Sam Harris
45:45
Actually I think this might punctuate this part of the conversation with the cases of various people who at least by their own testimony, have gone a fairway toward overcoming their personal need for sleep. And I think it was
Winston Churchill
who during the War years was sleeping The last 10 minutes of every hour or something like that.Share
46:09
I don't know if that's apocryphal, but what do we know about anyone's successfully thai trading their, their sleep down to something like a minimum? I'm sure there's there genotypes here that we may know something about where people just require less sleep than is normal.
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46:28
But actually I once had a doctor who claimed to sleep no more than 3.5 hours a night. And uh, you know, whether he was again, this is before the age of sleep tracking so he could have been delusional. But what do we know about people who sleep much less than you would recommend?
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Matthew Walker
46:50
Firstly from an epidemiological or population-based perspective, which is simply associational, using that sweet spot that we recommend, which is somewhere between 7-9 hours a night for the average adult, once you start to get less than that, the shorter your sleep, the shorter your life, that short sleep predicts all cause mortality.
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47:10
Are there people in history who have claimed to be short sleepers? There are and
Churchill
was one Edison
was another, although Edison
was a habitual napping during the day and he used naps and sleep as a creative tool, then you have Thatcher
, Margaret Thatcher
, you have Ronald Reagan
.Share
Sam Harris
47:29
You just named two people who ended their lives with Alzheimer's, So that's not a great commercial...
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Matthew Walker
47:36
It's exactly where I was going.
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Sam Harris
47:37
Yeah.
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Matthew Walker
47:37
Yeah, you know, they seemed if on the face of it to make it through until the, you know, fifties or even sixties, my goodness, there is evidential proof that you can sleep what they claimed to be sleeping, which is four hours a night and get away with it.
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47:54
And ultimately what we learned is that one way or another, sleep deficiency seems to get its hooks into you that the elastic band of sleep deprivation can stretch only so far before it snaps, and tragically for both of those individuals,
Thatcher
and Reagan
, they came to the disease of Alzheimer's.Share
Sam Harris
48:17
And we know before now realize we have several files open, but each of these seems important. So on that point, how do we disentangle association and causation here? Because I couldn't it also be true that one of the early symptoms of Alzheimer's or you know, being at special risk for it is to have one's apparent ability to sleep diminish over the course of one's life. Even it may be starting as early as one is 30 or 40.
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Matthew Walker
48:47
Yes. So we can go Alzheimer's disease is actually a great example. It's probably been I think that one of the most exciting areas of sleep research In terms of discoveries in the past ten or even five years we started with just those epidemiological associations, which are simply that the correlation is not causation and what that told us is that people who were sleepin...
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Sam Harris
49:10
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Sam Harris
Matthew Walker