Dr. Matt Walker: The Biology of Sleep & Your Unique Sleep Needs | Huberman Lab Guest Series

1. 0:00 – 2:24

   Importance of Sleep

   1. AHAndrew Huberman0:00

      (instrumental music) Welcome to the Huberman Lab Guest Series, where I and an expert guest discuss science and science-based tools for everyday life. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today's episode marks the first in our six-episode series all about sleep. Our expert guest for this series is Dr. Matthew Walker, Professor of Neuroscience and Psychology and the Director of the Center for Sleep Science at the University of California, Berkeley. He is also the author of the bestselling book, Why We Sleep. During the course of this six-episode series, for which we release one episode per week, starting with this Episode 1, we cover essentially all aspects of sleep and provide numerous practical tools to improve your sleep. For instance, we discuss the biology of sleep, including the different sleep stages, as well as why sleep is so important for our mental and physical health. We also talk about how sleep regulates things like emotionality, and learning, and neuroplasticity, that is your brain's ability to change in response to experience, and we discuss the various things that you can do to improve your sleep, everything from how to time lighting, temperature, exercise, eating, and the various things that can impact sleep, both positively and negatively, such as alcohol, cannabis, and various supplements and drugs that have been shown to improve sleep. We also talk about naps, dreaming and the role of dreams, and lucid dreaming, which is when you dream and you are aware that you are dreaming. In today's Episode 1, we specifically focus on why sleep is so important and what happens when we do not get enough sleep or enough quality sleep. We also talk about the various sleep stages, and we also talk about a very specific formula that everyone should know for themselves called QQRT, which is an acronym that stands for quality, quantity, regularity, and timing of sleep, four factors which, today, you'll learn how to identify specifically for you what your optimal QQRT is, and then to apply that in order to get the best possible night's sleep, which of course equates to the best possible level of focus and alertness throughout your days. Both Dr. Walker and I are very excited to share the material in this six-episode series with all of you, and as we march into today's Episode 1, I'm sure it will both provide a ton of excellent practical learning for all of you, as well as spark many questions that are sure to be answered in the subsequent episodes of this series.

2. 2:24 – 6:00

   Sponsors: Eight Sleep, BetterHelp & LMNT

   1. AHAndrew Huberman2:24

      Before we begin, I'd like to emphasize that this podcast is separate from my teaching and research roles at Stanford. It is, however, part of my desire and effort to bring zero-cost-to-consumer information about science and science-related tools to the general public. In keeping with that theme, I'd like to thank the sponsors of today's podcast. Our first sponsor is Eight Sleep. Eight Sleep makes smart mattress covers with cooling, heating, and sleep tracking capacity. Many times on this podcast, we discuss how in order to fall and stay deeply asleep, your body temperature actually needs to drop by about one to three degrees, and in order to wake up feeling maximally refreshed and energized, your body temperature needs to heat up by about one to three degrees. Eight Sleep makes it very easy to control the temperature of your sleeping environment so that it's easy to fall and stay asleep and wake up feeling refreshed. I started sleeping on an Eight Sleep mattress cover several years ago, and it has completely and positively transformed my sleep, so much so that when I travel to hotels or Airbnbs, I really miss my Eight Sleep. I've even shipped my Eight Sleep out to hotels that I've been staying in because it improves my sleep that much. If you'd like to try Eight Sleep, you can go to EightSleep.com/Huberman to save $150 off their Pod 3 Cover. Eight Sleep currently ships to the USA, Canada, UK, select countries in the EU, and Australia. Again, that's EightSleep.com/Huberman. Today's episode is also brought to us by BetterHelp. BetterHelp offers professional therapy with a licensed therapist carried out online. Now, I've been doing therapy for well over 30 years. Initially, I had to do therapy against my will, but, of course, I continued to do it voluntarily over time because I really believe that doing regular therapy with a quality therapist is one of the best things that we can do for our mental health. Indeed, for many people, it's as beneficial as getting regular physical exercise. The great thing about BetterHelp is that it makes it very easy to find a therapist that's optimal for your needs. And I think it's fair to say that we can define a great therapist as somebody with whom you have excellent rapport, somebody with whom you can talk about a variety of different issues, and who can provide you not just support, but also insight. And with BetterHelp, they make it extremely convenient so that it's matched to your schedule and other aspects of your life. If you'd like to try BetterHelp, you can go to BetterHelp.com/Huberman to get 10% off your first month. Again, that's BetterHelp.com/Huberman. Today's episode is also brought to us by LMNT. LMNT is an electrolyte drink that has everything you need and nothing you don't. That means plenty of the electrolytes, magnesium, potassium, and sodium, and no sugar. As I mentioned before on this podcast, I'm a big fan of salt. Now, I wanna be clear. People who already consume a lot of salt or who have high blood pressure or who happen to consume a lot of processed foods that typically contain salt need to control their salt intake. However, if you're somebody who eats pretty clean, and you're somebody who exercises, and you're drinking a lot of water, there's a decent chance that you could benefit from ingesting more electrolytes with your liquids. The reason for that is that all the cells in our body, including the nerve cells, the neurons, require the electrolytes in order to function properly. So, we don't just wanna be hydrated, we want to be hydrated with proper electrolyte levels. With LMNT, that's very easy to do. What I do is when I wake up in the morning, I consume about 16 to 32 ounces of water, and I'll dissolve a packet of LMNT in that water. I'll also do the same when I exercise, especially if it's on a hot day and I'm sweating a lot, and sometimes I'll even have a third LMNT packet dissolved in water if I'm exercising really hard or sweating a lot, or if I just notice that I'm not consuming enough salt with my food. If you'd like to try LMNT, you can go to Drink LMNT, spelled L-M-N-T, .com/Huberman to claim a free LMNT sample pack with your purchase. Again, that's Drink LMNT, L-M-N-T, .com/Huberman. And now for my conversation with Dr. Matthew

3. 6:00 – 11:40

   Sleep; Non-REM & REM Sleep

   1. AHAndrew Huberman6:00

      Walker. Dr. Matt Walker, welcome.

   2. MWMatt Walker6:03

      Dr. Huberman, it's an absolute privilege and a delight to be back.

   3. AHAndrew Huberman6:07

      That's right. You've been on here before, but-

   4. MWMatt Walker6:09

      I have.

   5. AHAndrew Huberman6:09

      ... during this episode in this series, we are going to go a lot deeper. By the way, you look very well rested.

   6. MWMatt Walker6:15

      Thank you very much. I actually slept pretty well last night, um, despite it being a, a foreign location. Um, same time zone, that helps just astronomically.

   7. AHAndrew Huberman6:26

      Amazing. Well, rather than ask you what a great night's sleep is for you-

   8. MWMatt Walker6:31

      (laughs)

   9. AHAndrew Huberman6:31

      ... because I am pretty sure you're gonna tell us that there's, uh, some individual differences that people need to pay attention to in terms of what is, quote/unquote, "optimal sleep."

   10. MWMatt Walker6:39

       Yeah.

   11. AHAndrew Huberman6:39

       Let's start off with the basics. What is sleep?

   12. MWMatt Walker6:45

       So, sleep, I think, in some ways, you can define as, at least in humans and, in fact, in all mammalian species, is broadly separated into two main types of sleep. On the one hand, we have something that many people will have heard of 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 (laughs) , increasing in their depth of sleep. So, stages three and four, the, that's the really deep sleep that we can speak about, and I should explain a little bit at some point what happens during that state within the brain. It's s- stunning. It's astonishing. So, you've got stages one and two, light non-REM sleep, when you sort of look at your sleep trackers and it has light non-REM, deep non-REM and, and REM. Stages one and two, that's light non-REM. Stages three and four, that's deep non-REM, and that's non-REM encapsulated. On the other hand, we have rapid eye movement sleep or REM sleep, and it's named not after the, um, popular Michael Stipe band of the 1990s, but because of these bizarre horizontal shuttling eye movements that occur during this stage of sleep, hence the rapid eye movements. And REM sleep is the... Depending on your definition, and we'll probably come to this in, in, uh, later episodes, it's the principal stage in which we dream, but if your definition is quite loose, which is any reported mental activity when I wake you up or when you wake up, then it turns out that we dream in almost every stage of sleep. But I'll describe REM sleep from here on in as perhaps, you know, dream sleep, and I'll make that faux pas. So, you've got these two types of sleep, non-REM and REM sleep. They will then play out in this beautiful battle for brain domination throughout the night, and that cerebral war is going to be won and lost on average for the average adult every 90 minutes, and then it's going to be replayed every 90 minutes, and that creates this standard cycling architecture of sleep. So, whoever is listening to this, when your head hits the pillow tonight, what will happen, you'll start to go down into the light stages of non-REM, then you'll go down into the deeper stages of non-REM sleep and you'll stay there, and after about 45, 50, 60 minutes, you'll start to rise back up again, and then you'll pop up and you'll have a short REM sleep period, and then back down you go again, down into non-REM sleep and up into REM sleep. And as I said, you cycle through that, on average, about 90 minutes, but I'll come back to that. What's interesting, however, is the ratio of non-REM to REM within your 90-minute cycle is not stable, and what I mean is, as you move across the night, the, the, the domination of those two types of sleep within the 90-minute cycle changes, 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, but very little REM sleep. But as we push through to the second half of the night, now that ratio balance, that seesaw balance shifts over, and instead we have much more rapid eye movement sleep and very little deep sleep. So, when people think about, okay, I just go to sleep. I lose consciousness. My brain is still. Firstly, nothing further from the truth could be the case in terms of your sleep. Second, your sleep has a very specific pattern that has consequences to real life. So, let's say that you're someone who normally gives yourself an eight-hour sleep opportunity in bed, but the next morning, based on what I've just told you, you say, "Okay, well, I want to... I'm gonna get a jumpstart on the day or I've got an early morning flight." So, I'm just going to come up with numbers here. I'm not suggesting that this is the ideal sleep schedule by any means, but just to make the numbers simple, let's say someone normally goes to bed at midnight and wakes up at 8:00. So, there's their eight-hour opportunity. But today, they're gonna wake up at 6:00 AM rather than 8:00 AM to get this push on the day. How much sleep have they lost? Well, technically, they've lost two hours of their eight hour, so they've lost 25%, but that's not entirely true. They may have lost 25% of their total sleep, but because of the strange structure of deep sleep first and then REM sleep later, they may have lost 60, 70, maybe 80% of their REM sleep. So, I only make this point because understanding how sleep is structured can have consequences.

4. 11:40 – 14:49

   Sleep Cycles, Individuality, Women vs. Men

   1. MWMatt Walker11:41

      I will come back to the 90 minutes though (laughs) . It's fascinating. We've often, and some people probably have heard this before, it's a 90-minute cycle. Well, there's huge variability. Some people can have a sleep cycle on average that's maybe 75 minutes, others 120 minutes.

   2. AHAndrew Huberman11:59

      Is it consistent within an individual?

   3. MWMatt Walker12:01

      It is r- relatively stable within an individual. So, I would say that the size of the difference from one individual to the next is much bigger than the size of the difference within an individual from one night to the next, to the next.

   4. AHAndrew Huberman12:17

      Not unlike a, a healthy menstrual cycle in a woman-

   5. MWMatt Walker12:21

      Correct.

   6. AHAndrew Huberman12:21

      ... which can range from-...as short as, you know, 24 days to 31 days and still be considered a healthy cycle that's regular, but-

   7. MWMatt Walker12:30

      Yep.

   8. AHAndrew Huberman12:31

      And it will change across the lifespan, of course, but for a good number of years, it's going to be pretty consistent within a given woman, uh, and yet between women, it can vary quite a bit.

   9. MWMatt Walker12:42

      Immensely.

   10. AHAndrew Huberman12:43

       Yeah.

   11. MWMatt Walker12:43

       And what's also interesting is that speaking about, um, some sex-specific things, there are sex differences. So on average, men, if you look at them, will have a sleep cycle that's about 15 to 20 minutes longer than women, which on a 90-minute average is actually quite a lot. And I bring this point up because you may have seen some of those s- claims or devices out there, well, firstly, probably on social media and people send me these things and say, "Is this true?" Which is you really have to structure your wake-up time at these very distinct 90-minute on the clock, when the clock strikes the 90-minute midnight, you know, that's when you have to be waking up and you should set your alarm.

   12. AHAndrew Huberman13:27

       Right. These, the, the rationale, you'll tell me that it's wrong, presumably, but the rationale of those devices is that one would be better off waking up at the end of a 90-minute cycle as opposed to in the middle of a 90-minute cycle even if it means getting less total sleep-

   13. MWMatt Walker13:46

       Yeah.

   14. AHAndrew Huberman13:46

       ...because the argument is that waking up at the end of a 90-minute cycle allows one to be more alert upon waking.

   15. MWMatt Walker13:53

       Right. That there's something uniquely special about the completion of a 90-minute cycle that will have you ejected out of sleep feeling like an Energizer Bunny, kind of, that's some of the claims that they've-

   16. AHAndrew Huberman14:03

       Y- And if I were to ask you now-

   17. MWMatt Walker14:04

       ... but that's nonsense.

   18. AHAndrew Huberman14:05

       ... true or false?

   19. MWMatt Walker14:06

       False. So sleep for as much as you possibly can sleep. Don't terminate that sleep artificially on the basis of anyone telling you that there is this kind of Da Vinci Code magic 90 minutes. That's unfortunately not true. And I, you know, I've been guilty of saying, you know, it's a 90-minute cycle and repeating that. So if I didn't know any better, I would believe that. So I'm not trying to, you know, chastise anyone. I'm just simply saying be aware of that and don't worry, don't stress about this unique 90-minute cycle. And there's some products out there that say they're going to time you on your 90-minute cycle and wake you up. I would probably stay a little bit clear of some of those.

5. 14:49 – 19:08

   Tool: Wakefulness in Bed, Insomnia

   1. MWMatt Walker14:49

   2. AHAndrew Huberman14:49

      What about going back to sleep? You said to get, um, as much sleep as possible. If I get six hours of sleep and then wake up and I feel like I could go back to sleep, would I be better off going back to sleep provided that my work schedule allows for that? Or, um, is it the case that after you've gotten a certain amount of sleep that it's a good idea to get up and, and go?

   3. MWMatt Walker15:07

      I would say that if you feel as though there's still more sleep in you.

   4. AHAndrew Huberman15:12

      Mm-hmm. There is.

   5. MWMatt Walker15:13

      Or- (laughs)

   6. AHAndrew Huberman15:15

      (laughs)

   7. MWMatt Walker15:15

      I love that this has become biographical instantly. Uh, it's gonna be a good episode when that happens. I would say hold tight, stay in bed, with an asterisk that I'll come back to, and see if you can get back to sleep. And we can speak about different ways of helping you do that. But the reason I put a, a slight asterisk there is the following. If you're then in bed for the next 45, 50 minutes wide awake, the danger, and it doesn't happen to everyone, but the danger is that you start to associate this thing called your bed with this thing called wakefulness-

   8. AHAndrew Huberman15:55

      Mm.

   9. MWMatt Walker15:55

      ...and not sleep. And one of the things that we do in cognitive behavioral therapy for insomnia is we try to prevent you from spending long periods of time awake. And I would say it's probably about a 25-minute rule of thumb, it's not a rule, it's a rule of thumb, if after about 25 minutes you just can't seem to catch it and this is happening frequently, I would just be mindful of you then starting to build a bonded association in your brain that your bed is also the place of being awake.

   10. AHAndrew Huberman16:25

       Mm.

   11. MWMatt Walker16:26

       The analogy would be y- you would never sit at the dinner table waiting to get hungry, so why would you lie in bed waiting to get sleepy? And the answer is that you, you shouldn't. And so we need to break that association. Now, there's nothing stopping you, however, from saying, "There's still sleep in me. I know that there is. So I'm just going to get out of bed, go to a different room, I'm just going to read a book, listen to a podcast, and then only when I feel sleepy I'm going to go back to bed because my schedule allows for it." That's the best way I would tell you if you still think there's sleep, uh, on the table, to try and get it back.

   12. AHAndrew Huberman17:07

       That's immensely valuable, uh, knowing that there's sort of a conditioned place effect of, of being awake in bed. Um, I must say, I get pretty good sleep most of the time. There have been phases of life, including recently, where sleep has been challenging and I notice as I head toward the bed to go to sleep recently, the words in my mind are, "Here's the battleground." Like, it's going to be a night-

   13. MWMatt Walker17:30

       That's right.

   14. AHAndrew Huberman17:30

       ...of going to sleep, waking up, going to sleep, waking up. We'll get to this business of s- of continuity of sleep a little bit later, so we don't have to go into that now, but-

   15. MWMatt Walker17:37

       I sh- I should also n- note, by the way, that for some people when I speak with them, they will, and it's just because you, you mentioned it, it's beautiful, they will be saying, "I- I'm so surprised because I am watching television and I'm falling asleep on the couch and then I get into bed and I'm wide awake and I don't know why." And that's because in part you've built this connection in your brain and it's, and when you go into the bedroom, that's what we try to do with cognitive behavioral therapy for insomnia. You s- spoke about it as a battleground, that it's almost this adversarial thing, which in some ways infers that at that point you feel as though your sleep controls you, and it is a miserable feeling. And gradually over time what we would do is work with someone and-... at that point now you control your sleep, your sleep doesn't control you, and that is such a freedom when you get it. But sorry, I interrupted you.

   16. AHAndrew Huberman18:31

       Oh, no, uh, I interrupted you, but, um, thank you. Yeah, I've prided myself, uh, my whole life on being able to sleep anytime, anywhere.

   17. MWMatt Walker18:38

       (laughs)

   18. AHAndrew Huberman18:39

       Uh, I learned it from my bulldog, Costello, or may- maybe that's what brought us together 'cause he certainly had that, that trait.

   19. MWMatt Walker18:44

       I'm so sad he's not here, uh, around anymore with us 'cause I would have loved... He feels like he is the best sleep ambassador. If there's a poster child for good sleep.

   20. AHAndrew Huberman18:52

       (laughs) Well, well, he's here in spirit, um, sleeping. Um, so this is interesting, and I think it's important for people to hear, if, if you can't fall asleep or if you wake up in the middle of the night and you can't fall back asleep pretty quickly, after about 20 minutes or so, probably best to get out of bed.

   21. MWMatt Walker19:06

       Yeah.

   22. AHAndrew Huberman19:07

       Um,

6. 19:08 – 27:05

   Non-REM Stages of Sleep

   1. AHAndrew Huberman19:08

      so these 90-minute-ish cycles that include different types of sleep, um, prompt me to ask, if you were to describe the basic characteristics of each of those four stages of sleep, and especially the deeper stages, three and four, and REM sleep, not just at the level of rapid eye movements during REM sleep, but in terms of the types of dreams or the characteristics of, of kind of bodily state, and, like, you know, maybe you could just flesh out the physiology and neurochemistry and, you know, touch on kind of the, the, uh, dream features associated with each of these, uh, different stages of sleep.

   2. MWMatt Walker19:47

      This just gets so exciting to me. And even now when I go into the lab or I look at sleep traces, um, from my sleep center, it, I am still in awe, in bewildered awe of what the brain does. So as we start to fall into those lighter stages of sleep, once you get past stage one sleep, which is sort of almost the shallows where you're just wading out, um, then you go into stage two sleep, and one of the hallmarks of stage two non-REM sleep are something called sleep spindles. And the way that we measure sleep in a laboratory, by the way, is that we place... You look like a spaghetti monster. You've got all of (laughs) these electrodes on your head, you've got things above your eyes, and you've got things on your body, and we're essentially measuring three main signals, electrical brain activity, we're measuring muscle activity, and we're measuring eye movement activity. And I'll explain why those three things are necessary for me to know, are you awake? Are you in sleep? And if you're in sleep, which stage of sleep you're in. So going into that stage two non-REM sleep, we've got these sleep spindles, and at that point I'm looking at the electrical signals from your brain, what we call the EEG or the electro, uh, encephalogram. And these sleep spindles are these beautiful, short, synchronous bursts of electrical activity and they last for about a second to two seconds, maybe a little longer, and they are bursting out of what we call a frequency of somewhere between 12 to 15 hertz, and what that means is that these brain waves are going up and down 12 to 15 times per second. That's what our measure is, 12 to 15 hertz. And then you go back and your brain at that point has started to slow down. Now when we're awake, your brain wave activity can be going up and down maybe 20, 30, 40 times per second. It's very fast and frenetic. It's actually very chaotic electrical brain activity. But as we're going into these lighter stages of sleep, then the brain starts to slow down, and at that point in stage two non-REM, it's maybe going up and down just four to eight times per second. So a huge deceleration in terms of brain wave activity. But occasionally you'll get these, sort of so it's going ʊʊ ʊʊ ʊʊ and then brr. You'll get these beautiful bursts of these sleep spindles. Um, I actually did, I, I sh- I've never published it, uh, publicly or, um... We did a project called the sonification of sleep and we took these electrical signals and then we turned them into sound waves. And you can actually hear this beautiful sort of ʊʊ ʊʊ, this, it's almost this beautiful throbbing of a slowdown in your brain, and then you'll hear these spindles, almost sounds like that beautiful, delicious rolling R in Hindi, so brr, this, it's just wonderful.

   3. AHAndrew Huberman22:41

      I'm not sure I can do that R, how does it go?

   4. MWMatt Walker22:43

      Brr.

   5. AHAndrew Huberman22:45

      Brr.

   6. MWMatt Walker22:45

      Yeah, not too bad.

   7. AHAndrew Huberman22:46

      Is that right? Okay.

   8. MWMatt Walker22:47

      Not, not too bad. I mean, we're erring on the side of feline, but that's okay, Andrew. (laughs) Um, so, so coming back to, I'm so sorry, um, coming back to sleep, we've gone into light stage two, as I'm trying to desperately hold it together, um, and we're going down into deeper non-REM sleep. Now something spectacular happens, and this is where I just almost l- lose it every time I see it. The brain now goes back down and its speed of, uh, for oscillation, of going up and down, is maybe just one or two times per second. It's incredibly slow.

   9. AHAndrew Huberman23:24

      And this is whole brain activity or localized activity?

   10. MWMatt Walker23:26

       This is, so we'll come onto this. At first the way we would measure it is just from these electrodes which are measuring hundreds of thousands of brain cells underneath them. So a good analogy would be let's say you're at a, a football stadium and it's Stanford playing Berkeley in, in American football, and what we've got is a single microphone dangling over the middle of the stadium and that microphone is picking up the summed voices of the 60, 70,000 people underneath. It's the same thing with when we place an electrode on your head. You're measuring the summed activity of hundreds of thousands of neurons underneath. But we've now started to use m- maybe 100, 200 electrodes on your head and we can pick these up in local territories of your brain. But that beautiful, powerful, slow brain waves, um, that we're getting during deep non-REM, stages three and four, it's not just slow activity. You would think, "Okay, that's, that, that sounds like the brain is dormant." No, no, the brain, at that point, the size of the waves is almost quadruple, maybe 10X the size of the brain waves when you are awake. Why is that? Meaning that the brain waves are going up and down very slowly, but the size of them, which is what we call the amplitude, that is now huge. It's epic. So think about it, you're on the beach-And when you're awake, the waves are coming in very, very quickly but they're small waves, and they're coming in in a random fashion. But deep slow wave sleep are these kind of epic things that would happen in Hawaii where you just get these 20, 30-foot waves, and they're coming in very slowly but they are epically big. That is deep slow wave sleep. And then what happens is riding on top of those big slow waves are these sleep spindles. They just keep coming. So according to the s- the sort of the sleep sonification project, what you would hear now these slow waves would be shoop, shoo, burr, shoop, shoo, burr. That's the slow wave and the sleep spindle. W- what is it that happens in your brain though, to your question, to produce these slow waves? Well, let's go back to the football stadium analogy. There before the game, that's wakefulness. Everyone is having a different conversation in a different part of the stadium and, and you just get this kinda incoherent sort of blabber that's going on. That's wake. Your brain is doing different things at different sort of locations of the brain processing, different information at different moments in time. And that's the fast phrenetic activity of wakefulness. When you go into deep sleep, all of a sudden for reasons that we still don't quite understand, hundreds of thousands of brain cells in your cortex all decide to unite in their singular voice of firing, and they all fire together and they all go silent together. They all fire together and they all go silent together. And that's what's producing these huge big powerful waves. So the analogy in the football stadium would be at this point now, and I'll, I'll come across to, um, to, to your university, Stanford is, is, is winning and the, the crowd is buoyant and all of a sudden the Stanford crowd is singing, "Berkeley sucks. Berkeley sucks." And they're all uniting. The whole stadium cries out at the same time and then goes silent at the same time. It's an epic display of coordinated neural activity in a way that we don't see in any other brain state. It's phenomenal. It's just enore.

7. 27:05 – 34:02

   Role of Deep Sleep

   1. MWMatt Walker27:05

   2. AHAndrew Huberman27:05

      You answered the question I was going to ask which is, does the pattern of brain activity that you just described occur in similar or identical form during any waking states? And I think you just said the answer is no, meaning if I understand correctly, this is a very, very specialized brain state unique to sleep, unique to a s- specific portion of sleep, and that begs the question what is it doing?

   3. MWMatt Walker27:33

      (laughs) So it turns out that all of these stages that we'll describe, different stages of sleep do different things for your brain and your body at different times of night. And it's very understandable that people sort of in the public will come over to me and say, "You know, how do I get more deep sleep?" Or "How do I get more REM sleep?" And my question back to them firstly is "Why do you want more REM sleep?" And they'll say, "Well, isn't that the good stuff?" (laughs) And I will say, "Well, it turns out that they're all important. You need all of them." But we can come on to... Let, let... I'll speak about non-REM sleep functions first and then I can probably, I should unpack REM sleep, um, and then explain its functions. But as an overview what we know is that during deep sleep first you switch over in terms of your body's nervous system to what we call the parasympathetic nervous system that you've spoken about a lot before, which is this kind of very quiescent calming state of your body's nervous system. The sympathetic nervous system, which is very poorly named 'cause it's anything but sympathetic. It's very aggravating and activating and, um, when we're awake that seems to be somewhat more dominant depending on what state you're in. But in sleep, especially in deep sleep, you shift over into this very strong parasympathetic quiescent calm state, and that instigates together with other things, um, and we've demonstrated by the way that we published a paper probably about a year and a half ago, that these slow waves and these sleep spindles and the coordination of them, how well that they're coordinated seems to instigate a signal down into your body's what we call the autonomic nervous system which carries both the sympathetic and the sympathetic nervous system inside of it, and forces you over into a parasympathetic state. So these brain waves, one of the things that they seem to be doing is transacting a message to your body's nervous system to say, "Calm down. Quiet down."

   4. AHAndrew Huberman29:32

      Mm-hmm.

   5. MWMatt Walker29:32

      What then happens, firstly what we see is your cardiovascular system ramps down. Deep sleep you could argue is almost the very best form of blood pressure medication that you could ever wish for. It's beautiful. Then something happens within your immune system. We're start- starting to unpack this but we still don't quite know why these pulsing deep slow brain waves seem to be a trigger for instigating two things for your immune system. Firstly, it stimulates the restocking of the weaponry in your immune arsenal so that you wake up the next day and you are a more robust immune individual.

   6. AHAndrew Huberman30:10

      So these are things like T-cells, natural killer cells-

   7. MWMatt Walker30:12

      Correct.

   8. AHAndrew Huberman30:12

      ... things of that sort.

   9. MWMatt Walker30:13

      All of that good stuff. But what's also interesting and there's a, a more recent discovery, um, it's not just that your body has, um, put back all of this armory in place and in fact amplified it, but your body's sensitivity to those immune factors has also increased. So you've restocked the, the weaponry and you've made your body more sensitive to those immune signals, and that's why we will see in probably later discussions your immune system can start to become w-... you know, really markedly impaired when you're not getting enough sleep. So that's a second benefit of the deep sleep, um, brain wave patterns. The third benefit that we've realized is that it's very good at regulating your metabolic system, and specifically your ability to control your blood sugar and your blood glucose. And if we selectively deprive you of just deep sleep alone, and we can do this now very cleverly. It's not as though I see you going into deep sleep and I go into your bedroom and I wake you up, and then you go back to sleep and... Which is how we used to do it, sort of, 10 years ago. Now, we can use a very clever method where we play auditory tones to your brain, but they are of a level that will not wake you up. It's what's called a subawakening threshold. And we determine that. And by playing those tones, it forces the brain to resurface out of deep sleep. So you will still sleep a total eight hours, but I will have selectively excised just your deep sleep. And when I do that, sure enough, your blood sugar ability, your ability to control your blood sugar I should say, is impaired really quite demonstrably, and it's for at least two reasons. The initial thing is that your pancreas, when it sees this spike in blood sugar, it normally releases something called insulin, and that insulin is a trigger to your body to say start absorbing the blood sugar so we don't get this toxic, or we don't maintain this toxic spike in blood sugar. Your pancreas, when you are under slept, and specifically when you're not getting enough deep sleep, does not release the appropriate amount of insulin. Worse still, what we found is that selectively depriving you of deep sleep means that what little insulin is released, the cells in your body become less receptive to that insulin. So you're not releasing enough of this chemical to say start absorbing blood sugar, and the cells that are designed to do the (inhales) they stick a straw out into your bloodstream and they (inhales) suck up the blood sugar, they don't respond to the insulin anymore. So on both sides of the blood sugar regulation equation you become impaired. And then I can give you an example upstairs in the brain, one of the things that we found, and we'll discuss, is that deep sleep helps regulate your learning and your memory functions, it helps start to move memories around in your brain and protect them and shift them from short-term to long-term. Deep sleep, however, we've now discovered, is critical for de-risking your Alzheimer's trajectory. It's during deep sleep when you have a cleansing system in the brain that starts washing away the toxic proteins that build up by way of wakefulness. And two of those toxic components are something that we call beta amyloid and tau protein, which are fundamental ingredients in the Alzheimer's disease brain equation. So certainly I could then understand based on that litany of things that I've just provided, and those are only a few of what deep sleep is doing, you could imagine that's the stuff that I want to get and that's the thing that I need to optimize for. Not true because there is REM sleep.

8. 34:02 – 35:15

   Sponsor: AG1

   1. AHAndrew Huberman34:02

      I'd like to take a brief break and acknowledge our sponsor AG1. AG1 is a vitamin mineral probiotic drink that also contains adaptogens and is designed to meet all of your foundational nutritional needs. By now I'm sure you've all heard me say that I've been taking AG1 since 2012, and indeed that is true. Now, of course, I do consume regular whole foods every day. I strive to get those foods mostly from unprocessed or minimally processed sources. However, I do find it hard to get enough servings of fruits and vegetables each day. So with AG1, I ensure that I get enough of the vitamins, minerals, prebiotic fiber, and other things typically found in fruits or vegetables, and of course I still make sure to eat fruits and vegetables, and in that way provide a sort of insurance that I'm getting enough of what I need. In addition, the adaptogens and other micronutrients in AG1 really help buffer against stress and ensure that the cells and organs and tissues of my body are getting the things they need. People often ask me that if they were gonna take just one supplement what that supplement should be, and I always answer AG1. If you'd like to try AG1, you can go to drinkag1.com/huberman to claim a special offer. You'll get five free travel packs, plus a year supply of vitamin D3K2. Again, that's drinkag1.com/huberman.

9. 35:15 – 42:00

   Light Sleep Stages, Hypnogogic Jerks

   1. AHAndrew Huberman35:15

      Before you talk about REM sleep, um, what about stages one and two of sleep? Are those just, um, kind of the jog into the, into the sprint-

   2. MWMatt Walker35:23

      (laughs)

   3. AHAndrew Huberman35:23

      ... that is, uh, deep sleep stages three and four? Or if I were to stage the question I'm asking as an experiment, say I'm an undergraduate or graduate student in your lab and I say, um, "Can we do an experiment where we selectively deprive people of stage one and two sleep only?"

   4. MWMatt Walker35:39

      Mm-hmm.

   5. AHAndrew Huberman35:39

      And, and then of course the question becomes what do you put in there instead? So there's a bunch of other experiments-

   6. MWMatt Walker35:44

      Yeah.

   7. AHAndrew Huberman35:45

      ... that one would have to, uh, do. But has that experiment ever been done? And if so, uh, what is the consequence of being stage one two deprived, um, as opposed to just deep sleep deprived?

   8. MWMatt Walker35:56

      So just as y- you already, um, elegantly demonstrated, that stage one selective deprivation is very difficult because it's a de novo thing you have to pass through to get to the other stages of sleep.

   9. AHAndrew Huberman36:10

      Is stage one the stage of sleep that I and other people have experienced many times where you're falling asleep and, um, you start to have a, a dream perhaps about walking or running and then you kick yourself awake?

   10. MWMatt Walker36:20

       That's right.

   11. AHAndrew Huberman36:20

       Okay.

   12. MWMatt Walker36:21

       Oh, and I should have explained what happens. Stage one I love. So as we're going into stage one, obviously our eyelids are closed, but one of the first signs that we know as we're recording, I told you we're recording the electrical activity on the head with these electrodes, but I also said that we're measuring eye movement activity. And as you're going into light stage one non-REM, for reasons that, again, we have no idea why, your eyeballs start to roll in their sockets...... underneath your eyelids. That change that we can start to see, we call them slow rolling eye movements and they are the hallmark of you entering sleep. And if you are lucky enough to have a partner, you can see this, it, you can, you know, as they're falling asleep, you will see these bizarre... Now, granted, if they wake up, usually the relationship is terminated very quickly because they're thinking like, "What are you doing?" (laughs)

   13. AHAndrew Huberman37:17

       Next time I'm on a plane, if the person next to me is sleeping-

   14. MWMatt Walker37:19

       Yeah, that's probably a better-

   15. AHAndrew Huberman37:20

       ... I'm going to be the guy kind of like, or, or a mirror... Yeah. No. Don't do that.

   16. MWMatt Walker37:23

       I'm the only one who gets away with it-

   17. AHAndrew Huberman37:24

       Yeah.

   18. MWMatt Walker37:24

       ... because I'm a card carrying sleep scientist. And even then, yeah, American Airlines sometimes take umbrage, but, um... So you get these slow rolling eye movements and the brainwaves start to, to sort of slow down again. But you mentioned something else, and they are called hypnagogic jerks. And as we're going into this first stage of sleep, I told you that the principal stage in which we dream is rapid eye movement sleep. It's not exactly true because everyone has had this experience that just as you're drifting off, you start to have these little mini dreams, almost sort of diet, or dreams lite, L-I-T-E. And y- you, you can almost wake yourself up based on the fracture point of cognition. And what I mean is, you're thinking, "Okay, so tomorrow, uh, I've got to get to the studio. I'm interviewing that desperately annoying British guy, Matt Walker. And then there was, uh, the elephant in the room with the helicopter wings on its head." And, and you almost just think, it wakes you up because you think, "Wait, wait, what? Sorry, excuse me, go back, r- rewind. What just happened?" That's the point at which you've transitioned over into the what we call the hypnagogic state where you can have these hypnagogic dreams, but you also get these jerks. W- we don't fully understand what happens, but the, what we do understand is that as you're going into sleep, you start to lose different aspects of your sensory perceptual apparatus. Not lose in the sense of where did I, where did they go and I can't find them, but th- the processing of those. Now, many will remain during sleep. One of the things that starts to degrade is what we call proprioception, and you've spoken about this before, which is knowing how your body is s- positioned in space. So it, it... Proprioception is fascinating. As you're walking with a colleague and you're crossing over a street, have you ever had that feeling where you, sort of, you step off the curb and you're chatting and all of a sudden you have one of those really ugly wobbles where you can... And it's because you had calculated, non-consciously and computationally, you understood where your foot was in space. You understood the velocity force with which it was descending down onto the road below you. You had miscalculated the distance and your brain had expected your foot to hit th- that road at a certain time and it did not. It sends an error signal back up your spinal cord and that's where you get that...

   19. AHAndrew Huberman40:00

       Yeah. This happened to me, um, uh, just last weekend. I was at the San Francisco Zoo and periodically throughout the landscape of the San Francisco Zoo, they have these kind of squishy surfaces that are seamless with the concrete around them. I think this is so kids can play on the, the various sculptures there.

   20. MWMatt Walker40:17

       (laughs)

   21. AHAndrew Huberman40:17

       And if they fall, it's a little bit more forgiving. So I was just walking across this thing, talking to the person to my left, and I stepped on this now rather squishy surface, and all of a sudden I was like, "Well, I don't know how to walk across this thing." And I'm like, you know, I've been walking on it long, a long period of my life. And I really had to pay attention. And then, and then transition back onto the concrete and could stop thinking about it for a moment.

   22. MWMatt Walker40:38

       Right. And you almost then have to stop the conversation that you were having-

   23. AHAndrew Huberman40:42

       Right. Right.

   24. MWMatt Walker40:42

       ... because it takes over and you switch from non-conscious proprioceptive and you switch over. So the issue is that when you are lying there awake in bed, you sense the mattress underneath you. You sense the support. You're getting all of that feedback signal that I was telling you was absent when you in- inappropriately calculated the distance down onto the road. All of that is in place and your brain is saying, "Everything's fine." But as we're drifting off into sleep, we start to lose that proprioceptive feedback. Now normally, that loss of proprioceptive feedback and sensation of what's going on and where my body is, is, is, is before the loss of consciousness. And so you lose consciousness and that's then thereafter when the loss of proprioception happens and you don't have this sort of, you know, mental freak out of, of proprioceptive break glass in case of emergency. But sometimes the speed with which those things happen changes and you start to lose the proprioceptive sensation before you fully lose consciousness. And at that point, your body says, "Oh, my goodness. Mattress has just disappeared and I'm falling."

   25. AHAndrew Huberman41:55

       Got it. Got it.

   26. MWMatt Walker41:56

       And that's where you can have these, these jerks. That's, that's our current best theory.

10. 42:00 – 49:09

    REM Sleep, Paralysis & Bizarre Dreams; “Falling” Asleep

    1. MWMatt Walker42:00

    2. AHAndrew Huberman42:00

       I know we're going to talk a lot about dreaming in a later episode of this series, but, um, what you just told me forces me to ask at this moment whether or not in dreams where we sense we are flying, is that possible because of the absence of proprioception? We- we're sort of, we're on the mattress or on whatever surface we sleep on, but according to the brain, there's, uh, we're suspended in space. Is that right?

    3. MWMatt Walker42:26

       Yeah. So it's, it- it's one possibility as to why we have those experiences. Uh, in some ways, though, it does bring us onto REM sleep. During REM sleep... And I'll explain what happens in the brain, but what you're talking about is something that is even more unique about REM sleep. As we go into REM sleep, your brain paralyzes your body, so you are physically locked into the incarceration of your body.... why would your brain do this? And it's what we call muscle atonia. Now, I was telling you that we measure your electrical brain activity and we measure your eye movement activity, but we also measure your muscle activity. Why do we do that? Well, as you're going into non-REM sleep, that muscle tone decreases, but there's still some muscle tone there. But as you go into REM sleep, in fact just a few seconds before you enter REM sleep, I already know you're going into REM sleep because, bang, you, you become completely absent of muscle tone. And if I were to pick you up and, I mean, I'm, I'm probably not gonna be able to pick you up out of your bed, um, based on certain images I've seen on social media. Um, I'm going to... Uh, if I lift you up, you'll just be like a rag doll. You'd have no muscle tone whatsoever. It's almost like those toys where it's like a donkey that sits up and it's got a button underneath and you press the button- Oh, I love those. ... whoosh, and it just falls down. Yeah. I used to have those as a kid too. Like, the simple things that you and I had as children- Yeah. I actually own- ... that were fascinating. ... I still own a couple of these. But they, but yeah, I need to get a donkey one, um, in any event. Um- But sorry. So- I know what you're referring to. So this, this muscle ato- as we call muscle atonia, anything in sort of medicine usually with an A before it means the absence of something. So sort of if you're, if you have arrhythmia, absence of normal arrhythmia. Aphasia .... right. Now, we don't know ultimately the origin of it, but I believe it's in part because people have this sense of falling, hence falling asleep.

11. 49:09 – 57:43

    Tools: Body Position & Sleep; Snoring & Sleep Apnea

    1. MWMatt Walker49:09

    2. AHAndrew Huberman49:09

       Along those lines, um, I've found that if I sleep horizontally on a bed or sofa, um, the sleep is far and away different than if I'm... Fall asleep upright in a chair or partially upright in a recliner-

    3. MWMatt Walker49:25

       Yeah.

    4. AHAndrew Huberman49:26

       ... um, for instance on an airplane. Now, there are a bunch of other things happening on airplanes, bright lights, noises, et cetera, um, so it's not a, a good experiment to compare those two situations, airplane recliner versus, uh, in bed at night.

    5. MWMatt Walker49:40

       Yeah.

    6. AHAndrew Huberman49:40

       Too many variables. Temperature, especially. But, um, is there any evidence that one's bodily position during sleep or the, uh, orientation of the feet relative to the head, you know, the angle elevated or, um, upward or downward has any impact on the, uh, pattern of, of different sleep stages or, uh, quality or, uh, any other aspects of sleep?

    7. MWMatt Walker50:02

       There is a reason for it, and we'll probably come onto this at some point when we speak about different methods for sleep optimization or the new wave of, of fascinating sleep enhancement tools has to do with temperature, we think. That for you to be able to fall asleep and stay asleep, you have to drop your brain and body temperature by just a little less than about one degree Celsius or probably two, two and a half degrees Fahrenheit. And that's the reason, by the way, that you will always find it easier to fall asleep in a room that's too cold than too hot, because the room that's too cold is at least taking you in the right temperature direction for good sleep, whereas the room that's too hot, the opposite. It turns out that the body's ability to dissipate heat, what we call thermoregulation here, and thermoregulation in one direction, which is the reduction in core body temperature, is superior when you are lying down versus when you are inclined versus when you are standing up.

    8. AHAndrew Huberman51:07

       Really?

    9. MWMatt Walker51:07

       And in part, it has to do with the distribution of blood throughout certain parts of the brain in the distal versus proximal regions, meaning sort of the regions that are closest to the core of your body versus the regions that are further away. But your body's ability, if we largely take most item, items of clothes off you and then we measure the, the core body temperature, and the way that we do this, um, is a delightful technique, it's called a rectal probe, and it's neither pleasant necessarily for the installation of the, the, the experiments doing it and it's certainly not necessarily for the participant, but putting that aside for a second, they... We can measure your core body temperature and we can measure using temperature sensors all over your body exactly what's going on with the blood flow and we can measure how the brain is starting to dissipate the heat because one of the principal ways that we dissipate heat from our body is by moving blood around the body. When we bring blood into the core of our body, we're trapping it in the core and our core body temperature increases. When we push that blood out to the surface, it goes to these thin sort of capillaries and vessels on the surface of your skin and you start to dissipate that heat, and you dissipate it more quickly, so your core body temperature drops. And the body's sort of vasoactive capacity for distributing that blood and then releasing that trapped heat from the core of the body is superior when you are lying down, and therefore your body temperature can drop more quickly which is one of the many reasons why it's not as easy to fall asleep when you're sort of at a 45-degree angle and why the quality of your sleep won't be as good. Now, there are other reasons too, just as you mentioned. But coming back to position, I would say that there are maybe... There's perhaps at least two pieces of evidence that would recommend positional differences or positional changes. The, the first is very obvious. If you are someone who is snoring and you have... Certainly if you have untreated sleep apnea, which is, um, where you're s- not just (snores) snoring, like, but you'll have an absence of breath. That's what the word apnea means. Here's another one with an A in front of it, pneia, sort of, you know, you've heard of p- pneumonia and it... This is about breath, and apnea is about an absence of that breath, and with sleep apnea, not only do you start to have an airway collapsing partially, and that's where you get that flutter and (snores) that's the sound of the flutter that we're having, but then at some point, you just hear silence. Uh, at that point, the person's stopped breathing entirely. Absence of breath. That is much more likely to happen if you are sleeping on your back because when you're sleeping on your back, your airway is giving way to gravity, which is wanting to pull the airway down and close it and shut it off. So one of the suggestions for people who have snoring or sleep apnea is trying as best you can to train yourself out of sleeping on your back. Now, there's lots of gadgets out there that can sort of help and ways you can do that. The old school way that we used to do it, um... Sleep apnea is more common in men than it is in women but women still have it, but if you had a male, you would bring them into the, the clinic and you would say, "Could you..." Um, it's often males who perhaps are carrying excessive body weight and so they're of larger mass size. You'd say, "Can you also bring a T-shirt in, uh, o- of your wife?" And it has to be a T-shirt that is... That has a pocket on the front. And then we would ask them to wear the T-shirt back to front, so it's a very tight-fitting T-shirt. It's back to front. And then you took a tennis ball or a hockey ball in the back pocket and as you're lying there in bed and you turn over onto your back, you get this...... painful signal of the tennis ball pushing you in the back and it gradually-

    10. AHAndrew Huberman55:20

        (laughs)

    11. MWMatt Walker55:20

        I know. It's-

    12. AHAndrew Huberman55:20

        Who came up with this? Is this Matt, was this, um, Matt Walker's idea?

    13. MWMatt Walker55:23

        This is not, this is not me. I am not the sleep-

    14. AHAndrew Huberman55:25

        It's cle- it's clever.

    15. MWMatt Walker55:26

        Yeah.

    16. AHAndrew Huberman55:26

        But it-

    17. MWMatt Walker55:26

        I should now be, on social media, I should be changed to sort of like sleep torturer rather than sleep diplomat. Um, so that's one recommendation.

    18. AHAndrew Huberman55:34

        Interesting.

    19. MWMatt Walker55:34

        Try to stay clear, if you're asking me are there certain positions we should stay away from, in that con- circumstance, yes, it would be. The other comes back to something I mentioned during deep sleep, when this cleansing system starts to kick into gear in your brain and wash away these toxins from the day. What we've found a little bit of evidence, and we and the royal we, 'cause I, um, like you, my lab doesn't do, um, animal research. We, we only do human research. But some animal researchers had discovered that when animals will sleep with their head on the side, that the cleansing capacity of the brain is superior than when the animal is sleeping on its back or sleeping on its front. And in fact, if you look, and you would love this project, if you go onto Google and you just search for sleeping animals, look at the head position, and I will guarantee you that many of them, if they're naturalistic, are animals with their head turned to the side. Now, the cute ones, the funny ones are when a, you know, a kitten is splayed out on its back and its head is back. That's how someone with sleep apnea would sort of sleep on their back and... But that's very rare. We almost never see that. So it's very interesting, and what they found was that when those heads were in those sort of side positions, the cleansing mechanism of the brain was a little bit better. It wasn't night or day. It's not as though, oh, my goodness, I'm a front sleeper and, you know, I'm not getting any brain cleansing, or I'm a back sleeper, I'm not... I'm not saying that. There's no need to take it to the extreme. But I, I don't think there's any good evidence yet in humans that firstly that's the case and nor is there strong enough evidence to make any recommendations, but I just bring it up because it's in the data and it's starting to emerge that if you were to ask me about sleeping position and are there any recommendations, those are the two pieces of descriptive advice I would give you. They are not prescriptive pieces of advice.

12. 57:43 – 1:04:03

    Yawning & Theories, Contagion

    1. AHAndrew Huberman57:43

       You mentioned the relationship between temperature and sleep, and we're going to get into that, uh, in some degree of detail a little bit later because it's so critical, but, um, prior to starting to record this episode, we were talking a little bit about...

    2. MWMatt Walker57:57

       (yawns)

    3. AHAndrew Huberman57:57

       ... yawning.

    4. MWMatt Walker57:59

       (laughs)

    5. AHAndrew Huberman57:59

       Um, and you told me something really truly fascinating about yawning, which was...

    6. MWMatt Walker58:06

       So there are at least four competing theories of yawning that we have, and I think there is probably a emerging clear winner. Um, the first theory was that it was just tiredness, that yawning is simply a sign of you being tired, and it turns out that that's not true because many people can yawn when they're bored and they are not tired and they've been very well-rested. So that doesn't seem to be true. The next one was one that, that seems to be very logical, which is it's about trying to rebalance your blood gases and specifically oxygen and carbon dioxide, and you would think that perhaps when you yawn (yawns) with that sort of, when you (yawns) and you inhale a huge volume of oxygen, what you're trying to do is pump back up the oxygen in your bloodstream, or (yawns) when you sort of (yawns) and the exhale, maybe it's about exhaling more carbon dioxide.

    7. AHAndrew Huberman59:06

       Not unlike the physiological sighs that occur during sleep of a double inhale with a long exhale.

    8. MWMatt Walker59:11

       Correct.

    9. AHAndrew Huberman59:12

       Or that one can voluntarily generate for anxiety management in wakeful states.

    10. MWMatt Walker59:15

        Exactly.

    11. AHAndrew Huberman59:15

        Yeah.

    12. MWMatt Walker59:16

        Yeah. And so that was a, a theory that maybe you're trying to balance these, these blood gases. And there were some very clever experiments where they took individuals and they artificially increased their oxygen, uh, levels, but more specifically, they increased their carbon dioxide levels bi-directionally. They tried to manipulate it, and they asked did those individuals start to yawn more, because the idea would be if your blood oxygen is coming down and your carbon dioxide is starting to rise, if this theory is correct, you should start yawning with greater frequency, and there was no difference whatsoever. That's probably also the reason that you don't see people yawning on a treadmill or when they're going into more of an oxygen debt and higher levels of carbon dioxide. So that theory was knocked out. The third theory was one of contagion, and it's fascinating. Yawning, like several other things, has a contagious element to it. So as the audience, unexpectedly, they didn't know what you were going to say and before you said it, you said, "You told us something interesting about..." (yawns) And you did it. I guarantee you that there will be people listening right now who said, "Oh, I just yawned in response to Andrew Huberman yawning." It is very contagious. In part, it's the mirror neuron system, and you, you, you obviously, uh, understand this in depth. Your brain has this capacity to mirror the action states of an individual. So a good example would be let's say I'm walking out the door now, I'm closing the door with my hand, and all of a sudden, I'm going to get my hand trapped, and you on the other side of the room, you are seeing my hand, and as soon as I trap my hand and I yelp out in pain, you almost hold your own hand...... oh, w- because why? Why, why are you doing that? It's not just because, y- y- you know, you're trying to be, you know, compassionate. No. You have experienced some degree of what I've just experienced. How does it do that? Because your brain has a system inside of it that mirrors my action states, and it's called a mirror system. And you can imagine why it's very good to understand the action and, and emotional states of others for pro-social capacities and all of that good stuff. And one of the things that can also happen with this mirror neuron system is that it mimics yawning. So when you yawn, my likelihood of yawning increases too, because my neur- mirror neuron system is matching your yawn. And what's interesting is that we know other species also have a mirror neuron system, and that means that when you yawn, there is a statistically higher chance that your dog will yawn and it's cross species. So when your dog yawns, (laughs) there's a higher probability that you will yawn. And we've got this data and it's, it's very clear. One of the other interesting theories, though, is that when, um, species that are cooperative species, for example, a pride of lions, when one of those lions yawns, firstly, many of the other lions will yawn in a contagious fashion, but then consequently, there is a collection of actions that happen after that contagious yawn. And so some people have suggested that the yawning is a way to enact cooperative group behavior. That's another theory. The final theory, number four, which I think has the best evidence for, is not the gaseous exchange balancing of carbon dioxide and oxygen, but when you inhale oxygen from the outside, it's usually cooler than your core body and brain temperature.

    13. AHAndrew Huberman1:03:11

        (gasps) .

    14. MWMatt Walker1:03:11

        And when we inhale, there is a modest drop in brain temperature, and when the brain temperature starts to rise, that's when we see yawning frequency beginning to increase. So next time you see someone yawn, don't think, "Oh, they're bored," or, "Mm, they didn't get enough sleep." Go over to them, hug them, and say, "I know your brain is getting warm. It's okay." And then at that point, the friendship will be terminated, 'cause no one should be hugging each other and saying, "Your brain is warm. I'm so sorry." But anyway, that aside, um, I'm sorry we, I took us down that, that, um, tributary of my polluted stream of consciousness, but that's yawning explained. Those are the four theories, and we don't have a definitive answer, but I think the best one right now that will continue is that it's about brain cooling.

13. 1:04:03 – 1:08:46

    Nodding Off, Afternoon & Postprandial Dip

    1. MWMatt Walker1:04:03

    2. AHAndrew Huberman1:04:03

       That theory makes a lot of sense. Um, people tend to yawn when they get tired. As you mentioned, people can yawn for other reasons as well. If I'm yawning because I'm tired and yawning is to cool off my brain that's too warm, is that an attempt to put my brain to sleep because we need to cool the brain in order for it to go to sleep?

    3. MWMatt Walker1:04:24

       Mm-hmm.

    4. AHAndrew Huberman1:04:24

       Or is something else going on there also? And this, um, sort of merges with the previous question about body position. I've lectured in the university for, you know, well over a decade, as I know you have as well, and occasionally, every once in a while-

    5. MWMatt Walker1:04:38

       (laughs)

    6. AHAndrew Huberman1:04:38

       ... there's one student... I'm just kidding. There are several students, especially if it's an afternoon class, uh, or a very early morning class, that is falling asleep in their chair, and then their head, they kind of jolt awake and we all know-

    7. MWMatt Walker1:04:51

       Yeah.

    8. AHAndrew Huberman1:04:51

       ... that keeping the room a little bit cooler sometimes helps to keep people awake, um, as opposed to a warm afternoon classroom.

    9. MWMatt Walker1:05:00

       Yeah.

    10. AHAndrew Huberman1:05:00

        But in some ways what we're talking about here, um, violates what you were talking about earlier, that it's easier to fall asleep in a cool environment as opposed to a warm environment. Uh, the brain needs to cool in order to fall asleep, but then when we yawn, it's in response to the brain being too warm, and so, um, and so I'm, I'm having-

    11. MWMatt Walker1:05:19

        Square that circle for me.

    12. AHAndrew Huberman1:05:20

        ... a little bit of a hard time. Yeah.

    13. MWMatt Walker1:05:20

        Yeah. Help me understand.

    14. AHAndrew Huberman1:05:21

        Yeah. Square, square that circle. (laughs) I like that. Yeah. Please square that circle for me, Matt. Um-

    15. MWMatt Walker1:05:25

        So it turns out that for you to drop your core body temperature, the opposite has to happen, which is that you have to warm up to cool down to fall asleep, and I mean warm up in a very specific way. You have to have the outer surface of your brain warm up. You have to get blood to the surface of your skin, and that surface is almost... acts like a snake charmer, that it draws the warm blood from the core and it pushes it to the surface, and you radiate the heat out, and as you radiate the heat out, as I said, your core body temperature plummets. So why would people be falling asleep sort of, you know, in an afternoon meeting when it starts to get a little warm? Well, in part it's because the warmth of the room is starting to make their sort of face a little bit more rosy. It's drawing the blood out to the surface. So what's happening, the core of your brain and your body temperature are starting to drop, and at that point, that's why you're going to start to feel a little bit more sleepy. That's reason one. The second that you described is that afternoon, you know, you're in meetings around a, a table and you start to get, as you said, those wonderful head nods, and p- people listening, you, you all know that where the s- head goes down and snaps back up. It's not that people are listening to good music and sort of doing this head bobbing. It's that they're falling prey to what we know is a genetically hardwired pre-programmed drop in your afternoon alertness. It's called the postprandial dip in alertness, and th- that infers that it's after some kind of a, a meal. It turns out it's not really related to a meal. People say, "Well, I had a heavy lunch. I had sort of pasta at lunch and I always feel sleepy afterwards." Maybe in part, but...... if I remove it, I f- I prevent you from having lunch, and we've done these studies too, your brain still shows this very reliable drop in alertness somewhere between, quite wide, but somewhere between about 1:00 to 4:00 PM in the afternoon.

    16. AHAndrew Huberman1:07:32

        Mm-hmm. Yeah, for me it's always between 2:00 and 3:00 PM, which, uh, is a time where-

    17. MWMatt Walker1:07:36

        So I'm resisting looking at my watch right now, just to see if I-

    18. AHAndrew Huberman1:07:38

        Yeah, we might be in that, in that, uh, phase of the day. Uh, I can always feel it, and, um, if I close my eyes for 10, 20 minutes, um, it, I usually can fall asleep pretty quickly-

    19. MWMatt Walker1:07:50

        Yeah.

    20. AHAndrew Huberman1:07:51

        ... for a nap. I know we'll talk about naps later. Um, but if I don't, and I ride it out, I, then, you know, usually by about 3:00, 3:30, I'm fine.

    21. MWMatt Walker1:07:59

        Get that rise back up, don't you?

    22. AHAndrew Huberman1:08:00

        Yes, yeah.

    23. MWMatt Walker1:08:00

        And it sort of swings back up. And so that's in part the reason though explaining th- the yawning and that, that warm feeling of I'm in the, the meeting room, the boardroom meeting, and the, the, the blinds are open. The sun is coming through. I've got the sun on my back. I'm starting to get very warm, but I'm starting to get really, really sleepy. It's the, it, it's the collusion of two things. It's that you're going into this higher frequency sleep zone in the afternoon, this postprandial drop in your brain alertness, and we can measure it. It's very reliable.

    24. AHAndrew Huberman1:08:33

        Mm-hmm.

    25. MWMatt Walker1:08:33

        You can see this dip in your brain electrical activity, and you're getting warm at the surface, which brings blood to the surface, releases that heat from the core, it drops, and boy, do you want to fall asleep.

14. 1:08:46 – 1:09:51

    Sponsor: InsideTracker

    1. MWMatt Walker1:08:47

    2. AHAndrew Huberman1:08:47

       I wanna take a brief break and acknowledge our sponsor, InsideTracker. InsideTracker is a personalized nutrition platform that analyzes data from your blood and DNA to help you better understand your body and help you reach your health goals. Now, I've long been a believer in getting regular blood work done, for the simple reason that many of the factors that impact your immediate and long-term health can only be analyzed from a quality blood test. The problem with a lot of blood tests out there, however, is that you get information back about metabolic factors, hormones, et cetera, but you don't know what to do with that information. With InsideTracker, they make it very easy to understand your results, and they also point you to specific directives that you can follow in the realm of nutrition, exercise, supplementation, even prescription drugs that can help bring the levels back into the ranges that are optimal for you. InsideTracker also offers InsideTracker Pro, which enables coaches and health professionals to provide premium and personalized services by leveraging InsideTracker's analysis and recommendations with their clients. If you'd like to try InsideTracker, you can go to insidetracker.com/huberman to get 20% off any of InsideTracker's plans. Again, that's insidetracker.com/huberman.

15. 1:09:51 – 1:14:09

    Sleep, Animals & Evolution

    1. AHAndrew Huberman1:09:52

       I took us on, uh, a bit of a journey into some, um, I don't wanna call them sidebars, but some, uh, specific features around sleep and falling asleep, et cetera. Let's get back to the different stages of sleep, and frame that under the question of what is great sleep? What is mediocre sleep? I think we all know what bad sleep is. It's when you can't get sleep, but I think there's a whole different category of bad sleep that you're gonna tell us about-

    2. MWMatt Walker1:10:20

       (laughs)

    3. AHAndrew Huberman1:10:20

       ... which is sleep that we think is good, but is actually not as good as we, we think it is.

    4. MWMatt Walker1:10:24

       I'm always the bearer of-

    5. AHAndrew Huberman1:10:25

       Yeah.

    6. MWMatt Walker1:10:25

       ... doom and gloom. Is the- (laughs)

    7. AHAndrew Huberman1:10:26

       No, but well, and, but also, but also the, um, the deliverer of, of powerful tools to improve one's, one's sleep, and thereby wakeful state. So along those lines, you know, what is sleep for truly and what happens when we don't sleep well is perhaps more intuitive to most people. You know, "Oh, I feel cranky," or, "I, I can't remember things," or, "I just gotta..." You know, um, stress seems to feel a little more intense. The same amount of stress feels more intense. Um, and what is great sleep? You know, and, and, and this is, I think, all under the umbrella of, of, you know, why do we sleep? I mean, why do we spend a good third to, you know, uh, or more of our life in, in this incredible state of mind and body that we call sleep?

    8. MWMatt Walker1:11:13

       And it really is quite stunning state of idiocy wh- (laughs) when, when you consider it, because when you're asleep, you're not finding a mate. You're not reproducing. You're not foraging for food. You're not caring for your young, and worse still, you are vulnerable to predation. (laughs) On any one of those grounds, but especially all of them as a collective, sleep should have been strongly selected against in the course of evolution. And in fact, one of the founding fathers of sleep research, Allan Rechtschaffen, once said that if sleep doesn't serve an absolutely vital function, it is the biggest mistake the evolutionary process has ever made. (laughs) And now what we've learned through, you know, almost 10,000 plus research studies over the past certainly 70, 80 years now, is that nature did not make a spectacular blunder in creating this thing called sleep. So maybe I can firstly address wh- what is, what is sleep doing, and what happens if we're not getting sufficient sleep? And then the other question is, wha- what is, what is good sleep? In terms of what sleep is doing and why he was right in saying that mother nature didn't make a, a blunder, and it hasn't, by the way, because if you go back, every species that we have carefully studied to date seems to sleep. And what that tells us, even, you know, very old, evolutionary old ancient, um, earthworms seem to sleep. They will have a period of what we call lethargicus, which is where (laughs) they seem to be inactive. So what I, I bring that point up because it means that sleep appears to have evolved with life itself on this planet, and then it has fought its way through heroically every step along the evolutionary path. And that by itself must tell us that whatever sleep is doing, it must be non-negotiably life support necessary.In what ways is it life support necessary? Well, we now know, many of those. First, when you're not getting sufficient sleep, I can speak about your hormonal systems. Let's say I take a group of really healthy young men, and I limit them to four or five hours of sleep for five nights. They will have a level of testosterone which is similar to someone who is probably 10 years older than them. So a lack of sleep will age you within five days by a decade. We also see equivalent imp-, uh, impairments in female reproductive health caused by a lack of sleep, impairments in estrogen, in follicle-stimulating hormone, and also in luteinizing hormone.

16. 1:14:09 – 1:27:13

    Poor Sleep & Health Consequences, Sleep Deprivation

    1. MWMatt Walker1:14:09

    2. AHAndrew Huberman1:14:09

       What, what about the f-, uh, effects of a single night's poor sleep on, on hormones?

    3. MWMatt Walker1:14:14

       Yeah.

    4. AHAndrew Huberman1:14:14

       Um, and not to get too down in the details here, but, uh, is it necessary to have four or five nights of minimal sleep in a row before you start to see these effects? Or let's say somebody's getting good sleep for three nights or four nights of the week, but then the other three are kind of challenging for whatever reason.

    5. MWMatt Walker1:14:32

       Yeah.

    6. AHAndrew Huberman1:14:32

       But does one see a graded effect, a kind of intermediate reduction in, uh, sex storage hormones like testosterone, estrogen, follicle-stimulating hormone?

    7. MWMatt Walker1:14:39

       There is some degree of a dose response curve, but we haven't mapped it out with high f- So the way I would want to do it as a sleep scientist would say, okay, I'm going to do this for one night, and I'm going to thin slice you to seven hours, six hours, five hours, and then I'm going to do it for two nights, and you're going to again be in the six hours, seven hours, four hours. And I would like to build up this high-fidelity map and understand that we don't have that. But certainly what we know is that a night of total deprivation will markedly impair those hormones, and we know that after about, you know, a working week of short sleep, you see those impairments too. Um, but let me come back to one night. So that's the hormonal system as an example, and we've already spoken, or I'll come back to it, um, right now, the metabolic system and another hormone, um, insulin. What we found is that if I take you again and I limit your... and you're perfectly normal, healthy, you don't have any signs of type 2 diabetes, and I limit you to let's say five hours of sleep for four nights, and then I measure your ability to dispose of blood sugar and, um... your level of blood sugar impairment is so disrupted that at that point your doctor would classify you as being pre-diabetic. So I could take an individual and within five nights of short sleep, I can move them towards a path that's getting very close to type 2 diabetes. And as I said, we've under... and we, uh, royal we, yeah. Uh, whenever I say we, by the way, it usually means that, um... Well, whenever I say I did something, I mean, at my center, we did something, and when I say we did something, I mean that they did something. (laughs)

    8. AHAndrew Huberman1:16:24

       That's a, that's a, a fair shorthand for, uh, for attribution.

    9. MWMatt Walker1:16:28

       Um, and so, so there have, there have been studies that have really decomposed exactly how that impairment in blood sugar happens, and we mentioned that earlier in this episode. I can also then move on to, for example, your, um, your immune system. This is a very good demonstration. Firstly, there's a great study done by Michael Owen and his colleagues at UCLA, and he took individuals, healthy individuals, and he limited them to just four hours of sleep for one single night, and he measured levels of critical anti-cancer fighting immune cells called natural killer cells. And what he found is that after that one night of just four hours of sleep, there was a 70% reduction in natural killer cell activity. That is a striking state of immune deficiency. And just to give people a, you know, a reference point, these natural killer cells, well, think of them almost like the Secret Service agents of your immune system. These natural killer cells, they are very good at identifying dangerous unwanted elements in your body, like cancer, and going after them and destroying them. So you wish for a very virile set of these immune assassins in your body at all times, and if you're not getting sufficient sleep, that may not necessarily be the case. We also know that if you are not getting sufficient sleep in the week before you get your flu shot, and this is just another example of how sleep is critical for your immune system, if you're not getting that s- sleep in the week before you get your flu shot, you produce less than 50% of the normal antibody response, therefore rendering that flu shot largely ineffective in terms of vaccinating you. We also know that if you're not getting sufficient sleep on average, let's say that you're getting less than six hours of sleep or less on average, you're almost three times more likely to develop the common cold, common flu. And I know that you, at the time of, uh, us r- recording this, um, you've released some fantastic content about the, the, the flu and, and the rhinovirus in particular. So that's a good demonstration of your immune system. We also know that it's not just that, it's also your cardiovascular system that suffers when you're not getting sufficient sleep. And here, again, the data I think is very strong, cardiovascular disease writ large, including stroke and, and heart attack. And there is one study that I think illustrates this, and, and granted now in terms of the replication, the effect sizes may not be as big, but the study was interesting. They didn't do something radical like depriving you of sleep for an entire night, nor did they just limit you to five hours of sleep for, you know, four nights. There is a global experiment, sleep experiment, that is performed on about 1.65 billion people across 70 countries twice a year, (laughs) and it's called daylight savings time.... now, in the spring, when we lose an hour of sleep, what they observed in that paper was a 24% relative increase in heart attack risk the following day.

    10. AHAndrew Huberman1:19:36

        Wow.

    11. MWMatt Walker1:19:36

        Yet, in the autumn, in the fall, when you gain an hour of sleep, there was a 21% reduction-

    12. AHAndrew Huberman1:19:42

        Amazing.

    13. MWMatt Walker1:19:43

        ... in hosp- so it's bidirectional, and by the way, and as I said, that, that paper there are, you can, there are some aspects that you can sort of discuss, but it has been replicated. We see increased rates of hospitalization after that one hour of lost sleep in the spring. There are higher rates of car accidents on the road after one hour of lost sleep. We also see higher rates of suicide after one hour of lost sleep during the spring time change. We even see it, this is great data, they, they looked at, um, the sentencing of federal judges in the United States, and because it's the federal system, the government system, all of those things are cataloged and well documented. So you have a huge database, and they went back, and what they found is that in the spring when we all lose that one hour of sleep opportunity, those judges doled out harsher federal sentencing (laughs) in the day after they had lost one hour of sleep because their emotional and mood states were impaired, and we'll speak about this in a later episode too. So if you're up for sentencing or pro- please try to avoid that spring time change as, as best you can. Go for the, go for the fall date if, if it's possible. Um, so that's, that's your cardiovascular system. I could also tell you that it goes all the way down into the cellular and molecular state of your body, and this, I'm trying to do this to impress the fundamental importance of sleep. There was a wonderful study done by my colleagues at the University of Surrey back in the UK by, led by Derk-Jan Dijk, and what they demonstrated was that if you take healthy individuals and everyone is going to act as their own control, and you limit them to, um, six hours of sleep for one week versus allowing them to sleep at least eight and a half hours or more time in bed. And then what they did was they measured the change in their gene activity profile relative to when those same individuals, as I said, were getting a full eight-hour-plus opportunity in bed versus the six hours of limited sleep, and they found two interesting things. First, a sizable and significant 711 genes were distorted in their activity caused by a lack of sleep. By the way, that's relevant. We know that almost one out of every three, maybe even one out of every two if you look at the data, people that pass you on the street, is trying to survive on six hours of sleep or less during the week. So it's a relevant ecological manipulation. The second result was that about half of those genes were increased in their activity, the other half were decreased. Now, those genes that were impaired by way of one week of short sleep were genes associated with the immune system. So once again, you can see this immune deficiency, but now playing out at a genetic level. Those genes that were increased, or what we call overexpressed, were genes that were associated with the promotion of tumors, genes that were associated with long-term chronic inflammation within the body, and genes that were associated with cellular stress, and as a consequence, cardiovascular disease. And to me, that study impressed the fact that there is no aspect of your wellness that seems to be able to retreat at the sign of sleep deprivation and get away unscathed. It's almost like a broken water pipe in your home, that sleep will leak down into every nook and cranny of your physiology, and it will even tamper with the very DNA nucleic alphabet that spells out your daily health narrative. So I, I paint this, this picture which seems dire and it, I think someone w- once said to me, "Look, your, your TED Talk," which I think was called "Sleep," uh, "Sleep Is Your Superpower," they said, "That talk should have actually been 'Sleep or Else...' " (laughs) which is a completely fair thing because I think, you know, very early on as a public figure for sleep, uh, um, I did a terrible job. I was very dictatorial. I was very-

    14. AHAndrew Huberman1:23:52

        Oh, I disagree.

    15. MWMatt Walker1:23:53

        Um, well, I was, I think I was very absolutist and I've, I've learnt my lesson, um-

    16. AHAndrew Huberman1:23:59

        I disagree and, and, um, and I'm going to interrupt intentionally-

    17. MWMatt Walker1:24:02

        (laughs)

    18. AHAndrew Huberman1:24:02

        ... uh, not to, to puff you up just because, but I, I think that it's fair to say, I know it's fair to say that the cautionary notes that you spoke about in those, uh, early TED Talks and in your book Why We Sleep, um, while they may have stimulated some anxiety for some people-

    19. MWMatt Walker1:24:21

        Yeah, right.

    20. AHAndrew Huberman1:24:22

        ... uh, they absolutely had and have a net positive effect in the sense that they cued people to the importance of this thing called sleep because prior to you doing that, or those things, it was the case that it was th- the, "I'll sleep when I'm dead," mentality.

    21. MWMatt Walker1:24:40

        Right.

    22. AHAndrew Huberman1:24:40

        Um, and as somebody who's pulled many all-nighters in his career, many, many, um, although not these days any longer, uh, thank goodness, um, I can tell you that that information was transformative for m- for my behavior and also for people in the arenas of military, sports, children, adults. I, I, it, it is fair to say that we have better parents, better kids, better citizens of every country as consequence. So I, I, uh, won't allow you-

    23. MWMatt Walker1:25:08

        (laughs)

    24. AHAndrew Huberman1:25:09

        ... it's one of the few things I'll, uh, I, you know, will, uh, have a hard line on, I won't allow you to, uh-

    25. MWMatt Walker1:25:15

        (laughs)

    26. AHAndrew Huberman1:25:15

        ... malign your contribution. Um, and the good news is w-... this series is also going to include a lot of discussion about things that one can do-

    27. MWMatt Walker1:25:24

        Absolutely.

    28. AHAndrew Huberman1:25:24

        ... anyone can do to improve their sleep, so.

    29. MWMatt Walker1:25:26

        Yeah. And I- I- I-

    30. AHAndrew Huberman1:25:27

        Enou- So enough with that, Walker.
17. 1:27:13 – 1:31:56

    Positive Effects of Good Sleep, Health Improvements

    1. AHAndrew Huberman1:27:13

       We hear less often about the great things that happen when we get great sleep.

    2. MWMatt Walker1:27:17

       Mm-hmm.

    3. AHAndrew Huberman1:27:18

       Um, perhaps we can talk about a few of those. I mean, obviously, um, many of them are going to be just the inverse of what you just described-

    4. MWMatt Walker1:27:26

       Yeah.

    5. AHAndrew Huberman1:27:26

       ... but, uh, for instance, learning, neuroplasticity, the nervous system's ability to change in response to experience. Uh, sleep deprivation impairs learning, yes?

    6. MWMatt Walker1:27:37

       Yeah.

    7. AHAndrew Huberman1:27:38

       Um, and a great night's sleep makes it a lot easier to learn, right? So wha- what are the data in- in terms of the relationship between sleep and learning? Again, something we're gonna go into in, uh, quite a bit more detail, but can you give us a, um, uh, can you- can you throw us a bone about-

    8. MWMatt Walker1:27:54

       Yeah.

    9. AHAndrew Huberman1:27:54

       ... some of the... Can you incentivize us for getting good sleep, not just through fear, but we heard the sticks, um, you know, throw us a carrot.

    10. MWMatt Walker1:28:01

        Yeah, so there are so many wonderful carrots. So when you are sleeping, your brain's capacity and its learning centers are so much more ready to absorb information. So think about y- these memory centers in the brain, almost like a dry sponge if you've been sleeping well, and they are so excited to soak up new information and retain that information. So firstly, sleep before learning is going to help you acquire and imprint new memories very effectively, and we've demonstrated that, and we'll- I'll tell you about the studies in- in a later episode. We also know, though, sleep after learning does something delicious. It will take those freshly minted memories, and it will consolidate them into the brain, meaning that it will start to fixate them, almost like sort of setting them in concrete into the brain, and so you are far less likely to lose those memories, which is to say you are far less likely to forget if you've been sleeping after you've learned. It's not just that, though. Sleep does more than simply strengthen those individual memories. Sleep will start to cross-link and connect those memories together, and as a consequence, the next day you will wake up and those- that memory back catalog has now been updated with all of the recent information, and it's integrated, and it's associated, so you are now able to come up with new creative solutions to issues or problems that you've been facing because you've updated what we call the associative networks in your brain. And this is the reason that people will describe having had these insights by way of sleep and these problem-solving capacities, and really, that's what... To me, a good student is not simply a student who can learn all of the individual rote facts and then just regurgitate them. An individual memory is not- as sitting as an isolate island is not particularly useful. That's why your laptop isn't... Well, uh, as long as it's not connected to the internet now and- and, uh, OpenAI, it- it's not particularly intelligent. I mean, it has a storage capacity that is almost more perfect than your brain. It doesn't make some of the- the memory sort of mistakes that we do. The reason it's not as intelligent as we are in part is because it has not integrated the information. It doesn't link all of the... Wouldn't it be wonderful if you woke up one day and you'd installed a program on your computer and your computer just understood how all of the files were interrelated and connected, and it was saying, "Okay, you- you know, you've double clicked on this file. Well, now I'm going to tell you that there is this related information, you should pull this in here, and it would enhance this paragraph that you're working on," or, "It would improve this experimental idea that you're coming..." It doesn't do that, but your brain does that. How does it do that? In part, it's because sleep is building these associative networks so it's not- it's not simply the student who learns the rote facts, it's the student who learns the facts and then understands what they mean.Sleep is not just about learning and it's not just about knowledge, it's about wisdom, which is knowing what it all means when you fit it together. And that's one of the other roles of sleep. So those are some of the beneficial things, the sort of, the- the- the carrots that can come by way of- for your learning and memory. There are so many other carrots, though. We described for your immune system how there is this restoration that happens during deep sleep, and it

18. 1:31:56 – 1:42:55

    Sleep & Mood; Appetite & Weight Management

    1. MWMatt Walker1:31:56

       primes that. But there are other benefits too. One of the things that we've discovered, and we hopefully will get to discuss this in more detail, is that sleep provides almost a rebooting of your emotional and your mood states. And as a consequence, you wake up the next day and you are dressed with a very different set of emotional clothing. And sleep, when you're getting it, almost it's like a set of emotional windscreen wipers that has just cleared those things off and you wake up... It's the reason that people will tell you, you know, you sh- i- if something is troubling you, don't worry, just come back tomorrow. Just give it a night of sleep and you'll probably feel better tomorrow. That feeling better notion is sleep acting as this emotional balm that just soothes that, those jagged edges that we've, you know, been sort of almost like a CD getting scratched, if anyone out there knows what a CD is these days. But, you know, these scratches that we get, emotional wounds, sleep is starting to heal those as well. So those are benefits. I could also mention some other aspects of your weight control and your weight gain, and this is a huge, huge effect size. Sleep moves the needle on almost every aspect of brain and body health. I think it's very clear at this stage that there is no single tissue or major physiological system in your body and no operation of your mind that isn't wonderfully enhanced by sleep when you get it, or demonstrably impaired when you don't get enough. But when it comes to appetite and regulation of weight gain, th- this is immense. Firstly, what we know is that when you're getting sufficient sleep, you can create a- a nice, um, concentration ratio of two appetite regulating hormones called leptin and ghrelin. And let me go sort of in the reverse, uh, to probably give you a better example. Let me say I deprive you of sleep. And what we see is that, uh, these two hormones that... And I joke, you know, they- they sometimes sound like, um, leptin and ghrelin sound like hobbits from Lord of the Rings, but they're not, they're real, uh, hormones. And leptin essentially is the signal that tells your brain, "Okay, you're- you're satiated by your food, you're full and you don't want to eat more." So hunger and appetite decrease. Ghrelin does the opposite. When ghrelin increases, now it's the signal of hunger and you get increasingly unsatisfied, despite eating a fill- full meal. If you've got still high levels of ghrelin, you don't feel satisfied with that meal. And many people listening may start to say, "I have this feeling where I'm just eating and I just don't feel satisfied on some days." And those days, I suspect, can be days when you are not sleeping well. And I think everyone has had this feeling of saying, "I just didn't sleep well last night and I al- I just get ravenous and my h- I just unleash this unholy hunger and appetite." That's in part because these two hormones. So what happens is that when we're not getting sufficient sleep, leptin, the signal that says, "You're satisfied with food, stop eating," that is impaired by way of lack of sleep. If that wasn't bad enough, the hormone ghrelin that says, "No, you're not satisfied with your food, eat more," that's the signal of hunger, that increases. So it's almost like double jeopardy. You're getting punished twice for the same crime of not sleeping. Once by way of a drop in leptin, stop eating, and once by way of ghrelin, foot to the floor acceleration, I want to start eating. That's in part why you're going to, your waistline can start to expand when you're not getting sufficient sleep. But when you do, it's a, it's a fantastic way of controlling. I guarantee you if you start to implement better sleep, your ability to regulate your basal levels of appetite and hunger will decline. But it's not just that you want to eat less or you at least want to eat an appropriate amount for your body mass, it's also what you want to eat. And what we've discovered is that when you are, again, not getting sufficient sleep, you start to eat more, yes, you do, but you eat more of specific things. You crave things like these heavy hitting, sort of stodgy carbohydrates like bread and pasta and potatoes and pizza, and also you crave simple sugars. And so those foods we know in excess can be what we call obesogenic foods. They are foods that can lead you to a more rapid amount of weight gain. Whereas when you are getting sufficient sleep, now you're reaching at the food bar for, you're saying, "Well, act- actually, I think the- the salad and those healthy nuts and the fruits and, those things look quite appetizing today." Versus when you are under slept, all you want to do is go after the junk food and, because you've kind of got these munchies. What's interesting is that a recent discovery came back to that notion of the munchies. When I say I got the munchies, people sometimes think of a drug reference, they'll say, "Well, I've been smoking weed, I always get the munchies." Uh, why is that? Because when you, when you are bringing in-... cannabis into the body and these cannabinoids, these what we call exogenous cannabinoids, they will increase your appetite. They will stimulate your appetite. Cannabinoids are appetite stimulating components. But we all have our own version of cannabinoids that we produce inside of our body, that you've s- spoken about before, called endocannabinoids. When you are under slept, the brain releases more endocannabinoids and that's in part why you get this strong impulse for... And thus, uh, go when you start sleeping better, you moderate all of these hormones and these chemicals and your appetite is controlled. When you eat, you feel satisfied with your food, you're not craving more. When you make your food choices, you're making better food choices. We did a study with brain imaging where we under slept individuals and we had them see food items inside of a brain scanner and they had to rate, you know, how much do I desire and how much do I want these items? And those items ranged from very healthy items all the way to unhealthy items. Things like ice cream and sort of pizza and all of that good stuff and, and sweets. Um, candy, as you would say over here. And we looked at their ratings. And by the way, we... To make this a more ecological... 'Cause you could say, "Well, th- they're going to know what's the healthy choice, so they're probably just going to be, you know, politically correct and say, 'Oh, I desire the healthy food,' because..." The way that we tried to get around that was we said, "Anything that you said was desirable when you come outside of the scanner, we've actually got all of these foods and you're going to have to eat them." Um, so they were making more realis- realistics. And each person went through the experiment twice, one night after a full night of sleep, one night with significantly less sleep. And sure enough, inside of the scanner, they were rating unhealthier foods as more desirable. So your preference was going in that unhealthy direction. But what was interesting was what was going on in the brain. We saw that the frontal lobe regions, these sort of areas that sit above our eyes that almost act like the CEO of the brain and they help regulate our deep emotional centers, those regions of the brain had gone offline by way of a lack of sleep. And these emotional centers that are usually associated with more hedonic reward and they're also excessively more active in people with obesity who have what we call hedonic eating patterns, those regions were ramped up by way of a lack of sleep. So it's not just that there are chemical changes in your body that conspire to have you eat more, there are also changes in your brain that prevent you from making the healthy food choices. But when you're getting sufficient sleep in the control condition, when they were getting that sleep, their brain was beautifully regulating the optimal food choices. So that's just another example of a car- (laughs) carrot, no pun intended now, um, that when you're getting sleep, if one of the ways you want to manage your, your body composition and manage your appetite is by way of getting sufficient sleep, it's actually a very powerful tool that we probably underrate. And then this other aspect, I would say, is emotional and mental wellness. Everyone knows that your emotional and mood states will take a nosedive like a dart into the ground when you're not getting sufficient sleep. It's that idea of I just snapped... And those are the words that usually, you know, are uttered by people who are not usually sleeping very well. But when you're getting good sleep, it's so much easier to regulate and manage those emotions. And Michael Grandner, great sleep researcher, he did a interesting study and it was one of those studies, like many studies I read from my colleagues, that my initial reaction to the study was jealousy because it was such a good study and I was jealous that I didn't think of the idea. And now gradually with my senior age, I've disabused myself of that ego and very quickly I then think, "This is the best paper and I can't wait to tweet it out." But he did a great study, and it was only quite recently. He asked, "What are the reasons that people want to try to improve sleep?" You would have thought that we'd have known this, you know, decades ago. And it's a relevant question to the point that you're asking, which is about these carrots. I know that there is still probably some degree of a sleep loss epidemic out there in the world. There is still that sleep machismo mentality that I can sleep when I'm dead. So how can we try to motivate people? Well, I can do it with the stick and I can do the whole sort of, you know, if it bleeds, it leads and do the doomsday stuff, and that can, that can motivate. But why don't I try to understand what it would be for most people that would have them try to enact better sleep behaviors? And they asked all sorts of different options, and the two things at the end of the paper when they did all the statistics that stood out like s- two sore thumbs. "I want to try to improve my sleep because I want to improve my mood. I want to improve my sleep because I want to improve my body weight." People know it. They already knew it. We didn't have to show them the data. And so it's just interesting, so I'm just bringing those two things up as a car- as carrot examples. There are many others, of course, too.

19. 1:42:55 – 1:47:57

    Sleep Deprivation & Looking Tired, “Beauty Sleep”

    1. MWMatt Walker1:42:55

Episode duration: 2:59:33