Dr. Matt Walker: How to Structure Your Sleep, Use Naps & Time Caffeine | Huberman Lab Guest Series

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 marks the third episode in our six episode series All About Sleep with expert guest Dr. Matthew Walker. During today's episode we discuss how to structure your sleep for optimal mental health, physical health and performance. We discuss monophasic sleep schedules, which are the more typical sleep schedule where you go to sleep at night and then wake up in the morning. So sleeping in one bout as opposed to polyphasic sleep schedules which are when you sleep in two or more bouts either at night or perhaps a shorter bout of sleep at night and another bout of sleep during the day. We also discuss naps, including how to nap, how long your nap should be, whether or not naps are good or bad, in particular whether or not they're good or bad for you. It turns out this varies according to individual we also discuss how your needs for sleep and nap naps vary across the lifespan and we discuss body position during sleep, which might seem excessively detailed, but it turns out that body position during sleep is critical for ensuring that the sleep you get is optimally restorative. As with the first two episodes of the six episode series, today's third episode is filled with both science, that is the biology of sleep and napping and body position and how those relate to one another, as well as practical tools that you can use to to vastly improve your sleep. 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 BetterHelp. BetterHelp offers professional therapy with a licensed therapist carried out online. 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 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.comhuberman to get 10% off your first month. Again, that's betterhelp.comhuberman Today's episode is also brought to us by Element. Element 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 want to 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 want to be hydra, we want to be hydrated with proper electrolyte levels. With Element, 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 Element 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 element 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 Element, you can go to drink element spelled lmnt.com huberman to claim a free Element Sample pack with your Purchase. Again, that's DrinkElementlmnt.com Huberman Today's episode is also brought to us by Waking Up. Waking up is a meditation app that has hundreds of different meditations, as well as scripts for yoga, NIDRA and Non Sleep Deep Rest or NSDR protocols. By now, there's an abundance of data showing that even short daily meditations can greatly improve our mood, reduce anxiety, improve our ability to focus, and can improve our memory. And while there are many different forms of meditation, most people find it difficult to find and stick to a meditation practice in a way that is most beneficial for them. The Waking up app makes it extremely easy to learn how to meditate and to carry out your daily meditation practice in a way that's going to be most effective and efficient for you. It includes a variety of different types of meditations of different duration, as well as things like Yoga Nidra which place the brain and body into a sort of pseudo sleep that allows you to emerge feeling incredibly mentally refreshing. In fact, the science around Yoga Nidra is really impressive, showing that after a Yoga Nidra session, levels of dopamine in certain areas of the brain are enhanced by up to 60%, which places the brain and body into a state of enhanced readiness for mental work and for physical work. Another thing I really like about the Waking up app is that it provides a 30 day introduction course. So for those of you that have not meditated before or are getting back to a meditation practice, that's fantastic. Or if you're somebody who's already a skilled and regular meditator, Waking up has more advanced meditations and Yoga Nidra sessions for you as well. If you'd like to try the Waking up app, you can go to wakingup.comhuberman and access a free 30 day trial. Again, that's wakingup.comhuberman and now for my conversation with Dr. Matthew Walker. Dr. Walker, welcome back Dr. Huberman.

An absolute pleasure.

Let's talk about the different types of sleep, because I think most people think of sleep as just one thing. Most people sleep at night. Some people also nap. A topic we'll also discuss today. But turns out there are a lot of different types of sleep. What are the different types of sleep and what do they do for us? And I guess everyone's probably wondering already. I certainly am. What types of sleep are we already engaging in? Meaning am I involved in or having multiple types of sleep each night?

This is a fascinating question and it comes back to something we've discussed in a previous episode. The different stages of sleep and how they unfold. We've described that fascinating stuff. What you're really asking, though, is an incredibly sort of subtle but relevant question. How should I be sleeping in terms of the phases of sleep? Should I have one phase? Should I have two phases of sleep? Or should I have many phases of sleep? In some ways you can answer that question on the basis of the lifespan because how it is that we sleep in terms of those chunking sessions changes as we develop. To be clear in nomenclature, I'm saying monophasic, biphasic, polyphasic. Unpack that. Monophasic obviously just simply means a single phase. Monophasic.

And when you say phase, you mean one bout of sleep.

Correct. So that would be within a 24 hour period you are having a single bout of sleep. Biphasic then means that within that 24 hour phase you are having two bouts of sleep. And we'll speak about how those bouts are split up. Are they split up between two halves in the middle of the night or are they split up in terms of longer at night siesta, like nap in the afternoon? And then we can speak about polyphasic sleep. Polyphasic sleep we in sleep science have been using for many years in the context of infancy. Because there, as any new parents will know, infants do not just simply have a nice single bout of sleep. They're up, they're down, they're up, they're down. And they have many bouts of sleep within that 24 hour period. And that's polyphasic sleep. The other term, or the other application of that term, polyphasic sleep, has been used more so in this sort of interesting biohacker movement. And we'll come back to that perhaps later on. So how do these different phases of sleep change across the lifespan? Well, we've already said that when you're an infant and you're first born within the first year of life, you are incredibly polyphasic and you are probably going through wake sleep phases every two hours. Why do you do that? Why can't you just simply be born and sleep in a monophasic way? It's for at least two reasons. First, an infant needs to feed every two hours. So their energy needs and their food intake requirements dictate that you can't sleep for very long because you need to be awake to feed. And then you go back to sleep within probably the first six months, things will start to change a little bit. But the second reason that you are highly polyphasic when you are first born is because your suprachiasmatic nucleus. And in another episode we spoke about this central master 24 hour clock that beats out your circadian rhythm, the rise and the fall, the wake and the sleep that has not yet developed. It hasn't been glued into place into the brain, this 24 hour clock. So the infant seemingly knows nothing about when it's light or when it's dark outside. They're just awake, asleep, awake, asleep. So that's the second reason. Energy feeding needs is the first. And then an absence of yet a fully developed 24 hour clock in the brain to beat out that beautiful dictated rhythm. By about age 1, that number of phases of sleep are starting to decrease. But it's still highly polyphasic. It's not until you get to probably age 2 or 3 that now you're starting to see this consolidation of sleep. What do I mean by that? Sleep is now happening more dominantly in the night phase of the 24 hour cycle. And there are a few abouts of sleep during the daytime. Then perhaps by the time you're in kindergarten, you may be down to just two sleeps. So now we've switched from polyphasic sleep as infants to biphasic sleep as kindergarten.

Could you describe that as biphasic patterns? I recall in kindergarten having nap time in the afternoon. It put out these little mats and every kid would just kind of like roll up. It actually sounds really nice.

It's one you know, wouldn't. And we'll speak about how some adults do this too. But almost every kindergarten system that I've inquired about around the world, different nations, they all have this nap time. And any teacher will tell you if one of those children does not nap during that period of time, they are the loose cannon. They are the live wire. And in subsequent episodes we'll speak about exactly how sleep harnesses and improves our emotional and mental health and how it falls apart when we don't. So that that's how it certainly is emerging biologically and that's how we as a society respect that and accommodate that. And then probably by the age of starting school, so sort of five or six now we're starting to see fully monophasic sleep. Children sleeping long bouts at night and then being able to sustain wakefulness during the day. At that point you have locked in your monophasic pattern. And that will continue throughout adulthood and into old age. With a few caveats that we'll speak about. So that's how sleep unfolds in the monophasic, biphasic, polyphasic sleep across the lifespan. It doesn't quite tell you however, how those different stages of sleep change across the lifespan. So I've shown you the view of sleep across the lifespan through one lens of the microscope. If we click down one lens and focus more deeply on the different stages of sleep, there we see a fascinating story in utero. For the most part you are in a sleep like state as a fetus once you get to a certain point of development in utero, that sleep like state seems to be more so something that looks like REM sleep. Now, it's not fully fledged full fat REM sleep yet, but it seems to be something very much like REM sleep. I say this because in the first episode, I told you, as we go into REM sleep and we start to, as adults, dream, the brain paralyzes the body so that the mind can dream safely. Those kicks and those punches and those elbows that a mother will feel from the fetus seem to be during this dream state often. And I don't want to shatter any illusions of you start singing or you're cooing and you get these bumps and these elbows and these legs kicking and it's beautiful. It is beautiful. But it turns out that it's probably the REM sleep state, but the muscle sort of paralysis has not yet developed. So you're getting these electrical bursts, this frenetic activity of REM sleep that we described, but you're not getting any of the blockade of the motor output. And so it expresses itself as these kicks and these bumps. And then during the first six months of life, and at that point in the first six months, those infants are sleeping anywhere between 14 to 17 hours a day. That's. It's immense, isn't it? I mean, it's right up there. If you look across phylogeny and you ask, which is, by the way, a fascinating topic, at some point we should do a separate podcast on sleep across different species, because I know, like me, you love, you know, the whole variety of species. But you've got elephants who will sleep as little as four hours. And then you've got the little brown bat who is the rock star of sleep. And it will sleep almost 17 to 18 hours a day. It nudges out the sloth in that sense.

Can I ask you a question about that little brown bat?

Yeah.

Does it sleep hanging upside down?

Does.

So it can't have sleep paralysis in.

Its little claws, so it will not have that paralysis. But it goes through the stages of sleep very quickly. And this happens with birds as well. So birds that flock on a branch, they will sleep. And they sleep in some fascinating ways, sometimes with one half of the brain, sometimes with both halves. But then you say, well, if I'm on a branch and there's this wonderful force called gravity underneath me, and I go into REM sleep and I have that muscle paralysis, which they do, how does that work? Well, they only have very brief REM sleep periods that last just for a few seconds and then they regain their muscle tone.

Got it. Couldn't help but ask.

It's genius.

The flora and the fauna.

Oh, I look, don't get me started.

But especially the fauna enchant me that much. So I don't want to draw us off course, but now we know that they can. That's why the bats don't fall. That's why the birds don't fall.

Correct. So when you are then as an infant sleeping 14 to 17 hours, what's happening with those different stages of sleep, non REM and rem. At that point, we can't really define and separate the different stages of non REM because it's not yet fully formed. But we have what looks like a REM sleep, active sleet and a deep non REM sleep passive state. Almost 50% of the time that an infant, a newborn, is asleep is spent in REM sleep. Why do I say that with some kind of wonder in my voice? Because as adults, we're perhaps down to maybe 20% of our time spent asleep is in rem sleep. But 50% of the time when an infant is asleep, they are in rem. Why would this be the case? And across all species that have REM and non rem, the time when we see REM sleep in highest volume amount is always after birth. There is something special about REM sleep and its function during that early period. And we now start to understand why. When you are first born, you are still going through a huge amount of brain maturation. And the recipe for the day there, unlike when we are teenagers, is exploding the brain with synapses, all of these connections throughout the brain. What we've discovered is that REM sleep acts as an electrical fertilizer to stimulate the growth of these connections within the brain. And it's almost as though you could think about an Internet service provider with this huge new neighborhood and the first call of business is to go in and wire up each one of those homes with these fiber optic cables. That's what REM sleep is doing. And if you start to deprive, and these were studies, gosh, done many years ago by Howard Rothwalk and others. If you deprive animals of REM sleep, you stunt the developmental growth of the.

Brain and presumably the whole animal.

And yeah, as a consequence, I mean, if you look at its social behavior, even just that, it's profoundly abnormal because you don't have that REM sleep developed brain. I mention this not because there is any causal evidence, but we have seen REM sleep impairments in certain developmental disorders such as autism, as well as adhd. I don't think there is any supportive evidence yet to come out with a claim that part of the trajectory underlying those conditions is abnormalities of REM sleep. But it's a very active area of research. So it's a fascinating time though, during infancy when you get these huge amounts of REM sleep. Why? Because of what we call synaptogenesis, which is simply the creation of synapses. Genesis. Then as you move from six months across the next 18 months, something odd happens. Total sleep time starts to decrease, REM sleep starts to decrease, but non REM sleep actually increases even though total sleep time is decreasing. And there's a strange peak in lighter stage non rem, what we call stage two, non rem. And those sleep spindles that I was describing in the first episode, these bursts of electrical activity, we will speak about the role of those sleep spindles in improving motor skill learning. And we've done many, many years of work in this area. Why is that relevant to this phase of life? That's right around the time when infants start to coordinate their limbs in a skilled way and begin to walk. And we believe that it is part of the process of the development of the motor system and enabling walking to begin.

Amazing.

So then things will change further. Sleep time continues to decrease and by about age 5 or 6 now, the cocktail blend of non REM and REM is down to a stable ratio that will remain throughout the lifespan, which is a 4 to 1 ratio. So about 20% of the time that you're asleep will be REM sleep. And the remaining time will be 80% of that time will be non REM.

Sleep, provided one is getting sufficient total amounts of sleep.

Correct. And getting it at the right moments in time that we described in the first episode, getting that sort of that appropriate chronotype match to the 24 hour clock, that will certainly alter those things too. So that's how sleep unfolds, both at the first level of the lens, monophasic, biphasic, polyphasic, and then double clicking. How the different stages of sleep unfold and what the reasons are behind that. I then said, once we're adults, we become monophasic. Yes, to a degree. But there is some contention about the way that we sleep in modernity, that we may not be sleeping in the way that we were designed to sleep. Which brings us back to biphasic sleep. In the first episode, we spoke about this strange afternoon dip in our alertness that happens called the postprandial dip. And it happens somewhere between the 1 to 4pm region and it's measurable and it seems to be biologically wired into us. If you look at certain cultures that are not touched by modernity, so we know this. Have studied hunter gatherer tribes. They don't quite sleep the way that we do and they don't sleep the way that we do for at least two reasons. The first is that they will often have a siesta like pattern of behavior where especially in the hot dry season, they will take a nap in the afternoon. In the wet, cooler season that may not be the case, but they certainly have more of a biphasic pattern where they'll sleep longer at night and then have a short nap, siesta like. And then of course there are Latin and Mediterranean cultures and they have this practice of the siesta like behavior. Coming back to the hunter gatherer tribes, the way that they also do not sleep in a similar manner to that which we do is their timing of sleep. They don't go to sleep as the sun goes down. They will usually, on average as a group, they will usually go to sleep about two hours after sundown and then they will wake up, not with the rising of the sun, they wake up just before that. And you think, how are they predictive of the light? No, the thing that changes first before the sun truly rises is temperature. And temperature is a very strong predictor that forces them awake. So when you think about how they're sleeping, then consider the term midnight. Most of us never really think about what the term means. Midnight refers to the fact that it is the middle of the night. But for most of us in the modern world, that's the time when we're thinking about sending our last email or posting to social media. Midnight is no longer midnight for society, but it is for them.

So should we be thinking about midnight as the middle of the night in the context of the extreme early person morning person who presumably likes to go to bed around 8pm, wake up around 4am Most people hear 4am and they go, oh goodness, that's early. Sort of like the mighty Jocko. Willink is famous for posting images he is of his digital watch. Usually I think it's 4:30am, wake up. And that's when he starts his workout. So his Twitter, I guess they call it X now feed and Instagram is replete with images of his watch 4:30. And people think, goodness, that's early. But he was a guest on this podcast, spoken to him before, but he goes to bed pretty early.

That's right.

Most nights. So in some sense midnight for him or for somebody with a similar schedule is truly middle of the night.

That's right.

But for the other chronotypes, for people that prefer to go to sleep or who naturally get sleepy around 10 or 11pm or even later, how should they think about this biphasic polyphasic business? Because at some level we all have to reconcile our sleep schedule with the demands of work and family and so on.

That's right. So I was very specific when I said the hunter gatherer tribes, on average, that's the way that they will sleep. But like the rest of society, there's a huge distribution and there will be some proportion of them who are a little bit like Jocko, who will be on the early side of that, on the very early side of that. But then there are other people who are clear night owls and they may not be going to bed until, you know, 10 or 11 and waking up later. So there is a distribution there. You don't have to worry that my statement of midnight on average, that does seem to be when we are dislocated from all of the trappings of modernity, how a group of representative humans on average will sleep. But there is huge, as I said, differences from one individual to the next. By the way, you can ask the question, why do we have these things called chronotypes? Why is there such variability in how people have a preference for when they sleep? Wouldn't it just be easier if biology designed us all to be asleep at the same time? Not so. We mentioned in the first episode that sleep is truly idiotic in the sense that you know you're not protecting yourself or the people that you care about. And if everyone slept at the same moment in time, you as a collective and as an individual would be vulnerable to, for an eight hour period, seven to nine hour period. But by way of this wonderful injection of variability as to preferences for when people sleep, maybe there are some people who are going to bed at 8pm and there are other people and they're waking up at 4am There are other people who go to bed at midnight and wake up at 8am so then think about that at some point, what you've done done is that there will always be someone or a collection of people awake until midnight and then will always be a collection of people who are awake starting at 4am so as an individual, everyone gets their eight hour opportunity. But as a collective, as a clan, you are You've reduced your vulnerability down by 50% because Mother Nature injected the variability by way of genetics of chronotype to distribute that and lessen the burden. Does that make any sense?

It does. And it reminds me of how the circadian rhythm, which we discussed in episode one, is about 24 hours, not exactly 24 hours. The rhythm of the suprachiasmatic nucleus, neurons that generate the circadian rhythm, as I recall, is rarely exactly 24 hours. It's 24.2 or 24.4. And the idea in mind, the gesso story, is that that variation allows for entrainment matching to the outside light dark cycle, which changes across the year. So you don't want it rigidly 24 hours, because if there's any variation in light dark, which of course there is, you know, even at the equator across the year, there's subtle variations, but certainly as you move away from the equator, and so these variations in, you know, your circadian rhythm clock, SCN, superchiasmatic nucleus might be 24.2, mine might be 24.6, someone else 24.1, and in that sense allows some malleability to matching the circadian rhythm to outside light dark rhythms. Is that a decent parallel for what we're talking about here?

It's a beautiful demonstration that there is always some, it's almost wiggle room in how biology is programmed because some degree of sort of noise, almost stochastic noise, can be very beneficial and it's much more predictive of the way in which the world works. And it's much more adaptive for a species to enact and to embrace that kind of variability. And yours was a beautiful example that it's about 24 hours, but it's certainly responsive to changes in light duration across the year. And it has to be because we need to buckle ourselves to the light dark cycle for optimal survival. And here is another demonstration of where it's not about the circadian rhythm, but it's about the chronotype distribution not within an individual across the year, but across individuals at any one moment in time. And that variability once again provides a biological benefit in the first episode.

And again now you're discussing chronotypes. And one thing that I've been meaning to ask is you said that chronotype is genetically determined, but does that necessarily mean it is directly inherited from mom and or dad? Meaning if your parents are both extreme early morning types, will you grow up to be an extreme early morning type? You already established that during infancy and development, adolescents, et cetera, that our chronotype is somewhat masked by some of the developmental necessities. But once we reach young adulthood and our chronotype has been established, can we look to our parents to determine whether or not we are more likely to be a morning person or late shifted?

It's very unlikely to find anyone whose parents were were both extreme morning types who is a neutral or an evening type and vice versa. So my guess is that people with, if they know of their biological parents and they know of their rhythms, it's highly likely that you will at some point acquiesce in your lifetime to being very similar to them. Now, there are certain life conditions and contexts where you can, you know, fight that. If you're really into, you know, if you're someone who is in punk rock band and you're touring all the time, even though your mum and dad may be morning types and you may be a morning type, you're on the road, you're playing gigs, there's no chance. But at some point, let's say you retire and you give yourself the opportunity to express your natural rhythm, you will go back to that. So yes, it's highly genetic. It's not entirely genetic. There is some degree of modification that happens on the basis of content, context. And I've just given you a good example of context and also your exposure to light. You can be someone who is, let's say, a neutral, like me. But if you're constantly invaded by electric light at night, you're drinking too much caffeine and you're on your laptop and your computer and your phone, and you're always activated by social media, it's very easy for someone like me to drift and become a 1am to, you know, 9am person. That's not my natural type. But context and the environment have shifted me. But for the most part, yes to your question.

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 going to 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 drink ag1.comhuberman to claim a special offer. You'll get five free travel packs plus a year supply of vitamin D3K2. Again, that's drinkag1.comhuberman okay, so getting back to these different phase opportunities for sleep. Clearly I'm getting the language wrong here, but no, it's lovely vernacular monophasic, biphasic and polyphasic. Could you give us a few more examples of different types of biphasic and polyphasic sleep?

So coming back to biphasic sleep, I describe one version once we are adults, which is the siesta like notion, one long bout at night, short about during the day. And that bout during the day is usually matching that drop in alertness that we described. It sort of hits that sweet spot right there. And it's quite easy for some people to fall asleep in that period between.

Somewhere between one and one to four.

Yeah. And I know it's a large window, but that just allows us to sort of know, okay, if you are someone like yourself who's a morning type, you would probably start to want to nap a little bit earlier. If you are biphasic, someone like me, a neutral, probably an hour and a half, two hours later still. But there is a different version of biphasic sleep for adults that has been described in the literature. And it's fascinating, but I don't think it's biological. It's the notion that some people will have heard called first sleep, second sleep. And now you are splitting your sleep into two phases, but they're split across the night. So the idea is that you fall asleep and you'll maybe have 4ish hours and then you wake up and you then are awake for several hours and then you go back to sleep for another three or four hours. If you look in history and the record of human history, it's very clear that there were some cultures doing this, particularly if you look at some of the European cultures, Great Britain in particular, There is good evidence that somewhere between about the 15th to 19th century seems to have ended during the kind of Dickensian era. People were describing this behavior and they would wake up in the middle of the night after about four hours. They would make food, they would play music, they would write, they would make love. It was a real thing. And I'm not suggesting that it did not happen. It clearly did. And there's a, there's a great book that outlines this. But is it the way that we were designed to sleep biphasically versus the siesta? Like, and I don't think it is. There is no good collection of evidence, if you look at the biology of our human rhythms, that argues that there is this magical period of a huge spike in our circadian rhythm that happens right in the middle of the night that should force us awake. There is one paper that's often cited for this, and in truth, that paper, if you read it, says nothing about first sleep. Second sleep doesn't speak about biphasic sleep at all. And that paper I think is unfairly used as a justification of first sleep and second sleep. And the paper to me has at least three problems. It's a great paper. There's no problem with the paper and its hypothesis, but, but its use as justification for first sleep. Second sleep has three problems. The first is the artificial nature of the study. They weren't designing it to test the hypothesis, but they had individuals in bed for 14 hours straight relative to a standard eight hour period. And sure enough, what they found was that when you force people night after night to be in bed for 14 hours, somewhere after about six or seven hours they wake up and then you can't get out of bed in the study, so you just lie awake. And then at some point, I don't know if it's through boredom or you drift back off into sleep. And that was argued as a clear demonstration of this split sleep. But as I said, they're awake usually for about six and a half, seven hours. Also, there was no magical awakening period. It's a probability distribution. And what that means is if you look at the data, it's just more likely that people will wake up after about six or seven hours and they're more likely that they will go back down into sleep. It wasn't as though the whole experiment demonstrated a very clear termination of sleep that everyone had at that moment in time. So that's the first issue. And the second issue, which is first issue, it's kind of an abnormal thing. 14 hours forced in bed. The second is it wasn't a clear separation, it's just simply higher probability. The final issue is that it was a study done in only seven individuals, healthy males. And so I have yet to see it scaled up. Did it happen? First sleep, second sleep? Yes, it did. Is there any strong evidence that that's how we naturally were designed and have evolved to sleep? In truth, I don't think so. At least I don't see good evidence right now supporting that, but remain open to it.

In episode one, we talked a little bit about body position during sleep and how different degrees of incline or decline might impact some of the features of sleep. And I can't help but ask now, as you described this biphasic pattern for people that were essentially experimentally restricted to the bed, is there something about being horizontal that makes us sleepy?

There is. And it's perhaps not for the reasons that you would think, which is, okay, I'm just pre programmed. When I lie down and my head hits the pillow, it turns out that it seems to be temperature that when your body is recumbent, lying flat, horizontal, the distribution of how your body is able to move blood around the different regions and decrease your core body temperature, meaning it can push blood, warm blood out of the core of your body to these surface areas. And when you push it out to the surface areas, you release that heat. It's this huge thermal dissipation that happens when we move blood out of the core to the surface. You emit that heat and your core body temperature plummets. When your body temperature, your core body temperature decreases, your, you have a higher likelihood of sleepiness. In fact, it's very difficult for you to fall asleep if your core body temperature does not drop. And by lying down, the body's what we call vasoactive ability to distribute that blood in a way that is permissive for thermal dissipation of core body temperature is superior. And that's the reason why we find it easier to fall asleep lying down than let's say semi recumbent or certainly propped all the way up. And it's probably the reason naturally we evolve just to lie down on the floor. Very interesting.

Maybe now's a good time to talk about biphasic sleep in the context of a bout of sleep at night and the afternoon nap. You've mentioned this postprandial diploma that most people experience between 1 and 4pm that many people try and combat with caffeine. We will also talk about caffeine this episode. Such an interesting substance and I think the most commonly used drug. It is a drug, after all, worldwide. I think more than 90% of adults worldwide consume caffeine on a daily basis.

That's correct. And I believe it is after oil. It may be perhaps the second or at least the third most traded commodity on this planet. And it is what we call a psychoactive stimulant. It is a stimulant and it's probably one of the only stimulants that we will readily give to our children and, you know, not be too concerned about it.

We'll get to caffeine in depth a little bit later in this episode, but I can't help but just mention that someone, I think it was Michael Pollan, said that, you know, caffeine is one of the few drugs that almost everybody takes just to, quote, unquote, feel normal. Yeah, exactly.

You know, it's sort of, I think sometimes, you know, sleep deprivation is, is simply just the absence of, of caffeine. And so it's a very interesting chemical which I have in truth changed my mind on. And I'm happy to speak about why I've changed my mind. But also some guardrails too.

We'll go there. Meanwhile, I'll take a sip of my triple espresso here as we discuss naps. Are naps good for us? Should we nap? What if we don't like naps, why do we wake up from naps groggy sometimes and other times we feel refreshed. Tell us about napping.

Naps are both good and bad, depending on the situation. Naps can be a double edged sword. In other words, we and others have done lots of studies on naps and the benefits are fascinating and stunning. I'll tell you about one study we did. We had participants assigned to one of two groups and at midday they all learned a whole list of new facts. So it was a study about learning and memory. And then one group took a 90 minute sleep opportunity, sort of focused right around that drop in alertness. The other just remained awake lying on a bed and they just watched a nature documentary. And then five hours later we had them do another learning session. And so they've woken up after the 90 minute nap. They've got through that sort of initial lull that we'll discuss what that is after you wake up. Everyone's now back to operating temperature. So in other words, I've had you try to cram in a whole list of facts at midday and then a whole list of facts, new facts again at 5pm And I can ask what is the learning capacity of your brain at midday and at 5pm? And is there any difference in your learning ability when you have had a nap in between versus not. And sure enough, what happened in the group that did not nap, their learning capacity gradually declined across the day. The nap group, they were able to sustain their learning and in fact if anything improve it. And the difference between those two groups at 5pm was about 20%. So that's certainly non trivial in terms of if you're to say, you know, here's a new compound that can boost your learning capacity by 20%, would you take it? I suspect it would probably make some money. So that's a demonstration of full learning and memory. We did another study very much like that in terms of its design, but we looked at your emotional brain and we were showing people different types of emotional expressions and having them rate them. And we did that firstly before a nap and then after a nap versus that same time in sort of midday versus 5pm and then another group did not nap. And sure enough, the group that did not NAP, by about 5pm they were starting to rate fearful faces and angry faces as much more fearful and much more angry. But if you looked at the group that napped, it was different. They actually lessened the response to fear and they blunted the normal increase in anger sensitivity across the day. And, and the nap seemed to boost how positively you rated happy faces. So a nap there had the ability to reset the magnetic north of your emotional compass. And there was a beneficial, almost added rose tint to your worldview glasses after you'd napped. What was also interesting in those two studies, two different types of sleep were transacting those benefits. In the nap group that was doing the learning. The learning benefit that they got wasn't just about them napping and sleeping, it was about them having these sleep spindles. The more of those sleep spindles that you had, the greater the restoration of your learning capacity when you wake up. For the emotional recalibration that I described in the nap, that had nothing to do with sleep spindles or even non REM sleep, it required REM sleep to produce that benefit. So there are certainly many benefits. And we've looked downstairs in the body. Blood pressure, cardiovascular measures, immune health, they all seem to benefit. So at that point everyone may be thinking, of course this sounds good, not to mention the basics, which is your attention, your concentration, your focus and your energy. All improvements by way of naps. Even your decision making.

You said decision making?

Yeah, even your decision making is improved. So your capacity to make the correct decisional outcomes based on this weight of evidence that you're facing, that's also improved. So almost all areas of cognition that we've looked at and many areas of your emotional and mood health we've looked at seem to benefit by way of a nap. At that point, you're thinking, so then what's the problem? The problem is that when you nap, you release some of that sleep pressure that's been building up. So in the first episode, we spoke about a chemical called adenosine. And the longer that you're awake, the more adenosine that builds up. The more adenosine that builds up, the sleepier you will feel. And after about 16 hours of being awake, you should have lots of healthy sleepiness of adenosine in your brain to put you asleep and keep you asleep. And when we sleep, we are able to clear that adenosine from the brain. So we wake up after seven to nine hours. And if it's been good quality sleep, we're refreshed because we've cleansed the brain in part of that adenosine. When you take a nap, like a pressure valve on a steam cooker, you just release some of that healthy sleepiness that you've been building up. So the dark side of napping is if you are struggling with sleep and you suffer from insomnia, the advice is do not nap during the day because you're setting yourself up for an even higher probability of failure at night. Why? Because when you nap, you release some of that good sleepiness that we need to build up for you as someone who is struggling with sleep, to give you the greatest chance of a weight of sleepiness on your shoulders. So if you are not struggling with sleep and you can nap regularly, I would say naps are just fine and we can unpack. What is an optimal nap and the protocol for what napping should be? I would say that's great. The only caveat is make sure that you're not napping too late into the day. And this is one of the components of the protocol of how to nap. Because napping late in the day is too close to sleep, and you can think of it almost like snacking before your main meal. A nap late in the day just takes the appetite edge off your sleepiness so that when it comes time for sleep, you're not as hungry anymore. So just keep that in mind. But we can unpack. Perhaps the optimal way to nap. If you are going to nap and exactly the do's and the Don'ts of that. If that sounds of somewhat interesting.

Yeah, that is of immense interest to me and I know many other people. I'm a huge believer in naps. I've always enjoyed short naps of about 10 to 30 minutes unless I'm somehow sleep deprived, in which case I will sleep for an hour or even a little bit more. But I make sure I set an alarm really based on advice that you gave me which was to first of all decide whether or not a nap is beneficial for me or for whoever is considering that. But then to make sure that however long that nap is zero to 90 minutes, that it not be longer than 90 minutes. Because the real goal is to not disrupt nighttime sleep.

That's right.

Which is essentially just a more long winded way of saying what you just said. So how does one determine the optimal duration of nap? And in particular to avoid the problem of disrupting nighttime sleep by napping. But also this rather common phenomenon of waking up and feeling kind of groggy or even kind of grumpy. The post nap face, or we should call it the post nap expression.

Right. The pne.

What's your pne? Do you wake up in the. And for morning too. Somebody will wake up and they're like, like that, that face. And then there's the like good morning. You know, and I think people that wake up with the good morning are particularly delightful. Unless you're of the post nap expression that is kind of the crumpled face and then you just, you don't want to be around those people. No, absolutely, yeah, yeah. And this probably relates to spirit animals and things like that. Some people wake up like a, like a cheerful chipmunk and other people seem to wake up like my bulldog Costello where it's, you know, jowls still in contact with the floor.

Yeah. So peony, I'm trying to hold it together and not absolutely just fall apart. It's brilliant. Please trademark it. So firstly to your question how to optimally nap. The word optimal is interesting because when people say how long should I nap? What's the optimal nap duration? The question I have back to them is what are you trying to optimize? Because once I understand what you're trying to optimize, I can give you a better prescription non medical, I'm talking about here a better sort of, you know, protocol piece of advice for how to nap. I mentioned the study about emotional faces in part for a specific reason because I told you there the benefit came by way not of non REM sleep, but REM sleep And in our first episode we said that when you go through these on average 90 minute cycles, you get most of your non REM sleep first and then you'll have this bout of REM sleep at the end. And it always seems to go that way. When you are a healthy, normal person, you go into non REM sleep and then you go into REM sleep. It's very rare that you ever go directly into REM sleep. There are only two reasons when that seems to happen. The first is a clinical condition called narcolepsy where you can have sleep onset REM sleep and it's very rare. The second is if you are horrifically deprived of REM sleep night after night after night, I let you sleep then at that point REM sleep, the pressure for REM sleep has been built to the point of being almost just insatiable and your brain goes straight into REM sleep. But with those two things aside, you go into non REM sleep first. So I brought up the emotional study of resetting your sort of mood, compassion, because to get that REM sleep you had to nap for a longer period of time because you had to get through the non REM sleep first before you get the REM sleep. But let's come back to then assuming optimal is for most people when they speak about naps. I just want the quick reboot. I want my alertness and concentration, which are failing because I'm staring at the screen or I just can't concentrate on the work that I'm doing. I want my alertness and my concentration to be improved. I want that sort of slight boost in brain energy where I know I can sustain myself for now, a longer period of time. And I've got the motivation, which is really in some ways how I like to think about energy as well. I've got the motivation, the drive to keep going, which is just starting to fail me, to get those basic things, which is what most people nap for. Aim for a 20 minute nap. Why 20 minutes? If I thin slice the nap duration and those studies have been done where we look at essentially what's called a dose response curve, I give you five minutes of a nap, 10 minutes of a nap, 15 minutes, 20 minutes, 30 minutes, 45 minutes, 90 minutes. After five or 10 minutes you don't really get very much. You will wake up and you'll have some degree of improved alertness and your basic reaction time may be a little bit quicker, but that fades very quickly and you don't sustain that benefit. Once you get past about 15 to 17 minutes now things start to look different. You get these nice benefits for concentration, alertness and motivation and those things sustain. So once you wake up out of that probably really, I would say 20 minute nap, at that point you've got some good wind in your concentration and energy sales for the brain. And that will sustain you throughout the rest of the afternoon and into the evening. The benefit of the 20 minute nap is that you don't get the PNE trademark Andrew Huberman. You don't get that almost sleep hangover. So some people will say it's strange. I nap, maybe I'll nap 45 minutes, 50 minutes and I wake up. And to be honest, Matt, I almost feel worse after the nap than I did before. And I don't understand it. It's something called sleep inertia. And an extreme version of this is in the first two hours of your night of sleep, you get a phone call or an alarm goes off and you wake up and you are just kind of lost in the ocean. You're looking around at your surroundings, you're just in this groggy state. You're half awake, half asleep, and you can respond and you can do things, but boy does it feel miserable. And it's almost as though you're going from the ground floor right up to the penthouse suite, but you get stuck somewhere in between, kind of, you know, floor 13. And it's this rough state. If you go out into sleep light stage one non rem, then stage two, non removal. And just before you get into the very deeper stages of non REM, 3 and 4, that starts to happen around 30 to 40 minutes for most people. But by cutting your nap off at 20 minutes, you still get these nice benefits from a good chunk of healthy non REM sleep. But you're not going so far into the cycle, so deep into your non REM that when you wake up after 20 minutes, you're not in that, what we call sleep inertia phase, that sleep grogginess, that sleep hangover phase. So it's a nice benefit that you get all of these improvements in your brain, but you wake up and very quickly you're back up to operating temperature and you don't suffer that inertia. Now that's not to say that when you sleep or you nap longer, you don't start to get more benefits, you do. And those benefits are both greater in their magnitude and sustain for a longer period of time. They do. It's just that you have to understand the trade off that you will suffer, which is I will get more bang for my buck and I will get more benefits. But I will, in the first sort of hour or so, have to understand that at that point I may even be functioning worse than that which I did before I even started napping. But if you're patient and you go through it, the rewards on the other side are significantly better still. So that's the first piece of advice. And when it comes to how to nap, I would say the dose and the timing make the poison, and poison is hyperbole here it's simply just the poison being how much sleep inertia you're going to suffer. So aim for about 20 minutes. That's the dose. The timing comes back to that which we described before. Do not nap too late into the day. So what's the rule of thumb here for a protocol? On average, for the average adult, I would say don't nap after about 3pm, 20 minute naps sometime between 3pm and if you're struggling with sleep, don't do this at all. If you're not and you're able to get to sleep, fine. This seems to be a good ingredient for the basic return on your investment. Again, if you tell me what's the optimal nap duration, we need to have a conversation to understand what is it that you're going after here? What are the benefits? And then I can sort of create a finger buffet kaleidoscope match to what you need and we can think about the nap duration as a consequence.

Thank you, that's very informative. I have a colleague at Stanford who's a Howard Hughes investigator, which for those that don't know is a rather elite club of academic researcher. They have to essentially try out for it every five years they go up for renewal. It's a lot of money, which gives them a greater capacity to take on greater risk work, higher risk work. And he's also a member of the National Academy. And he was one of these people who graduated high school at 15 years of age, one of these phenoms. And he is so religious about his napping such that when he travels to give seminars at other schools, he insists that they schedule a nap time for him after lunch and in his office, you know, between 12:30 and 1:00pm he's napping. Everyone knows this, and I mention this because I think that oftentimes people think of the nappers as the lazy ones. But his output is near superhuman. And he attributes much of that output to, to the nap, not just the post nap work that he's able to perform. But his ability to just kind of manage so many ideas. He has an enormous laboratory. And that's just one example. I think there are examples from sport of sprinters taking naps on the, you know, on the side of the track field. I mean, so it seems that a capacity to nap is also something worth considering because I think many people listening to this are thinking, well, I can't nap, should I nap? And can one teach themselves to nap? So that's the question if one would want to explore napping. And is that something that one should even consider doing? If you don't have a propensity to nap, should you avoid it? If you want to try naps, how could one teach oneself to nap? You just mentioned earlier, lying down relates to body temperature, body temperature relates to sleepiness. And then as a third question, I promise I'll repeat these if we need to. As a third question, I'd like to have a little bit of a discussion about some of the pseudo nap states that I certainly am intrigued by. For instance, just lying down. And I'm doing a progressive bodily relaxation things like Yoga Nidra, Non Sleep, Deep rest, which is an acronym I coined simply to make it clear what I was talking about. But it's very similar to Yoga nidra, things of that sort. In other words, put simply, should everyone think about having an early to mid afternoon protocol to reset their cognition in their body? We call it a nap, but does it have to be a nap? And if we're not good nappers, should we try and if so, how should we go about it?

Yes. So to your three questions, firstly, if you're not a natural napper, should you start doing it? If you want to start doing it, how should you do it? And then the third is, is this some kind of, you know, substitute for a like kind, which would be these, these. I love the phraseology that you use. These liminal states, do they mimic that? Are they different to that? How should we think about those? The first thing I would say to point number one, if you are not a natural napper, don't necessarily force yourself to be. As long as you're getting the sleep that you feel you need at night and you feel refreshed and restored during the day and you don't have that sort of postprandial drop to the point of thinking I almost need to nap during the day, there is no pressure based on anything I've been telling you for you to start napping, nor should there be any reason that you do start napping. But let's say that you want to try. What would be the right protocol to improve and increase the likelihood? The best way you can do this is to mimic nighttime as best you can. So wherever you are, if you can shut off the lights, make sure that you can block out curtains, blinds. If you can't do that fully. And many people won't be able to develop an eye mask procedure. So put an eye mask on. Make sure you block out noise. Earplugs. You can use a sound machine if you want, and we can speak about sound machines and whether or not they're good or bad on sleep.