The Tim Ferriss Show Transcripts: Dr. Matthew Walker, All Things Sleep Continued — The Hidden Dangers of Melatonin, Tools for Insomnia, Enhancing Learning and Sleep Spindles, The Upsides of Sleep Divorce, How Sleep Impacts Sex (and Vice Versa), Adventures in Lucid Dreaming, The One Clock to Rule Them All, The IP Addresses of Your Memories, and More (#654)

Please enjoy this transcript of my interview with Dr. Matthew Walker  (@sleepdiplomat), professor of neuroscience at the University of California Berkeley and founder and director of the school’s Center for Human Sleep Science. Dr. Walker is the author of the New York Times and international bestseller Why We Sleep: Unlocking the Power of Sleep and Dreams, which was recently listed by Bill Gates as one of his top five books of the year. His TED Talk, “Sleep is Your Superpower,” has garnered more than 17 million views.

He has received numerous funding awards from the National Science Foundation and the National Institutes of Health and is a Kavli Fellow of the National Academy of Sciences. In 2020, Dr. Walker was awarded the Carl Sagan Prize for Science Achievements. Dr. Walker’s research examines the impact of sleep on human health and disease. He has been featured on numerous television and radio outlets including 60 Minutes, Nat Geo TV, NOVA Science, NPR, and the BBC. Dr. Walker is also scientific advisor to Oura, a sleep-tracking ring.

Dr. Walker hosts the 5-star-rated podcast The Matt Walker Podcastwhich is all about sleep, the brain, and the body.

And one last thing. UC Berkeley has given the rare approval for Matt’s newly opened Sleep Center at the University to be named by an individual donor, or a named company, in perpetuity. If you are interested, please reach out to Matt and note that this opportunity is in the 7-figure range.

Transcripts may contain a few typos. With many episodes lasting 2+ hours, it can be difficult to catch minor errors. Enjoy!

Listen to the episode on Apple Podcasts, Spotify, Overcast, Podcast Addict, Pocket Casts, Castbox, Google Podcasts, Stitcher, Amazon Musicor on your favorite podcast platform. You can watch the interview on YouTube here.

#654: Dr. Matthew Walker, All Things Sleep Continued — The Hidden Dangers of Melatonin, Tools for Insomnia, Enhancing Learning and Sleep Spindles, The Upsides of Sleep Divorce, How Sleep Impacts Sex (and Vice Versa), Adventures in Lucid Dreaming, The One Clock to Rule Them All, The IP Addresses of Your Memories, and More


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Tim Ferriss: So sleep and sex. Let’s dive into this wide and exciting topic. Where should we begin in a discussion of sleep and sex?

Dr. Matthew Walker: Maybe we could start with how sleep impacts sex, and begin with actually the literal idea of separating those bedfellows, and to the question of, should you have a sleep divorce as a couple to prevent a real one?

Tim Ferriss: And sleep divorce is sleeping separately?

Dr. Matthew Walker: That’s right. Yeah. So a sleep divorce is where you will sleep either in separate locations or at least in separate beds. The diluted version of the sleep divorce, rather than sleeping in separate rooms and separate beds is called the Scandinavian method, which you think — it sounds so much more salacious than it actually is, which is, essentially, you’ve just got two separate beds that you put side by side, and that’s the diet version of a sleep divorce. But I do think that sleep divorce idea is important because it is a taboo, and it also can markedly improve things for people.

So when we’ve looked at survey data, both in the US and also in the UK with The Sleep Council there, what you find is that about one out of every four couples who are surveyed will tell you that they have had a sleep divorce, that they will sleep in separate beds. And we think that that may be in part an underestimate because of the stigma associated with it. And if you survey people anonymously, you get to a number of — almost one out of every three people will admit to waking up at least in different locations.

And there is pretty good evidence from the science as to why that number may make sense, why 25 percent of all couples suggest that — when we study couples who are sleeping together objectively on almost every measure that we can quantify about sleep, sleep is worse when you are sleeping as a couple relative to when you are sleeping separately. The twist in the tail there though is that when you ask people about the satisfaction of sleep, there is definitely some group of individuals that say, “Look, I feel more satisfied with my sleep when I’m sleeping with my partner than when I’m sleeping separately,” despite the fact that objectively their sleep is worse. So I’m not suggesting it’s a one size fits all, but I think the taboo comes from the idea that, “Well, if you’re not sleeping together, then you are not sleeping together.” And the exact opposite is true.

Tim Ferriss: That’s British for having intercourse? Is that what that means?

Dr. Matthew Walker: Thank you very much, yeah. We just get over this. It’s my desperately unfortunate Hugh Grant genes that has me trying to navigate around the topic rather than just saying it straight. So thank you, Tim. Yes. If you’re not sleeping together, then you’re not having sex, you’re not having intercourse.

Tim Ferriss: Yes.

Dr. Matthew Walker: But the — oh, come on, Matthew. Hold it together. But it turns out that the opposite is true, that when you get a couple who are sleeping well, their sex life actually improves. And it’s probably for three reasons that we’ve uncovered. The first is hormones, the second is sensitivity, and the third is libido. And I’ll try to park my Hugh Grant and get right into it. In terms of the hormones —

Tim Ferriss: Take off the gloves, Matt, take off the gloves.

Dr. Matthew Walker: Come on. It’s time. I’m wondering what you mean by saying take off the glove in terms of this conversation, but let me just skip it. You see, you opened the door, Tim, and I walked right into it.

Tim Ferriss: Oh, here we go. Here we go. Or put on the gloves, if you prefer.

Dr. Matthew Walker: Yeah, I think probably best — but we know each other quite well now, so maybe — anyway, so in terms of the hormones. Firstly, we know that testosterone, gosh, it takes a pretty sharp nose dive in males, and in females when you’re not sleeping well. Males who, if we put them on a diet of maybe four or five hours of sleep, they drop their levels of testosterone somewhere by about 10 years of aging. So a lack of sleep will age a man by a decade in terms of virility. It’s also true of estrogen in women. And so when those two sex hormones are not in play, you get a reduction in the quality of the sex life.

The second component, and this is data that we’ve only really got in females, less so in males. But the sensitivity of female genitalia increases when sleep is in high volume versus when people are not getting sufficient sleep. And we think that’s due to the estrogen, that when estrogen is in normative amounts because you’re sleeping well, there is greater vaginal lubrication, which therefore leads to greater sensitivity and greater pleasure by way of sex.

And then the final aspect is libido. We’ve also found that when a woman obtains an extra one hour of sleep, there is a 14 percent increase in her desirability to be intimate, to have sex with her partner. And I find that interesting because if you put it in context, the FDA-approved drugs for increased libido in women, things like, I think it’s called Vyleesi, it’s one of them I know. That will increase libido in women by about 24 percent. But here is the simple addition of one hour of extra sleep, you can get more than 50 percent of that benefit drug free.

Tim Ferriss: Question for you, Matt. How are these drug companies measuring increases in libido? Is it a self-reported one-to-10 scale or something like that, which can be very sort of fungible?

Dr. Matthew Walker: It is self-reported. So many of those scales are subject. It’s very much like pain. When it comes to libido, it’s somewhat difficult to quantify. And of course, it’s not just about innate biological libido, the conditions have to be right. You have to have the relationship with your partner. Which actually also reminds me, by the way, when couples are not sleeping well — and this is a study from UC Berkeley, not from my lab. But what they found is that they have more fights, they don’t resolve conflict nearly as well between them when they’re having a fight. And the reason is because you lose empathy. When you are not sleeping well, your ability to empathize with other individuals, and we now have demonstrated why in terms of the brain networks. You decrease that capacity for understanding the other. And no wonder you’re fighting, and you’re fighting in a pretty poor way.

Tim Ferriss: What’s the playbook? What’s the best practices?

Dr. Matthew Walker: I’m not suggesting that a sleep divorce is for everyone by any means whatsoever. There are some people for whom they adore sleeping with their partner for lots of reasons, safety, security, intimacy. But I think if you are interested in it, take a graded approach. And I would suggest firstly, just having an open, gentle conversation, and don’t be defensive about it. The second is, don’t suggest that it’s permanent. Offer the idea that, “Look, could we do this, darling? Could we do this for the next week or the next two weeks? And I’m not suggesting it’s forever. Let’s just see, and let’s just try it on for size.”

Then I think what people misunderstand about sleeping together in the same bed is what they miss. They don’t really miss the majority of time, because for the majority of time you’re asleep, you’re unconscious. What you really miss are the bookends of sleep. That sort of getting into bed, having a cuddle, saying “good night,” and in the morning, waking up and doing the same thing. So if you have a sleep divorce, what you can also do is build that in. So whoever goes to bed first, the other person comes in, you have your time, you sort of cuddle, do whatever you need to do. And then you leave and repeat the same process in the morning. You don’t have to do that every day, of course, it’s not going to be practical. But in that way, you sort of get the benefits of sleeping together whilst still having a sleep divorce, if that makes some sense. So I would just say be honest with yourself.

Tim Ferriss: I feel like sleep divorce needs a rebrand. Maybe furniture polyamory, since you’d be on separate pieces of furniture. Sounds really sort of risqué, taboo, kind of sexy.

Dr. Matthew Walker: I am so stealing that because when you bring that up in a dinner conversation and you finally admit it to your friends, they all think, “Oh, no, they’re on the rocks.” But furniture polyamory, all sorts of swings from the ceiling and — 

Tim Ferriss: Oh, it sounds very exciting. Very exciting.

Dr. Matthew Walker: Yeah. Yeah. Candle wax on the nipples, let’s go.

Tim Ferriss: They’re killing it, yeah.

Dr. Matthew Walker: Exactly. “Honey, we’ve got to switch things up if they’re doing that.”

Tim Ferriss: Yeah. So a question that has always been unanswered for me. I have some theories, but why is it — and this is my assumption just based on broad strokes, having had conversations with many people about this and observed this also online. It seems that men tend to run hot and women tend to run cooler, in the sense that men will often want the temperature in the room to be lower, the sheets or the bedding to be thinner. I mean, this is part of the reason why I use devices like Eight Sleep’s, not the only thing out there. They do sponsor the podcast, but I used them before that, so that you can have zones of temperature. I don’t know if this is something you’ve looked into it, is that mostly attributable to muscle mass and thermogenesis? Is it hormonal? How do you explain that if — do you have an explanation?

Dr. Matthew Walker: Yeah, it’s muscle mass, thermogenesis. It’s also regarding — and thermogenesis really comes onto metabolic rate, and then it’s also hormonal based on testosterone, which is in part a thermogenic hormone in and of itself. That temperature difference, we can measure and we can see it. Actually, studies were done before we were looking at this, not related to sleep, but just related to core body temperature. And they demonstrated that there are some age dependencies to it though, that once you get past about 50 or 60, the differences between men and women start to collapse and they start to become much more similar to each other than they are different. Why is that? It could be in part because of the reduction in testosterone. That happens also because of the muscle mass degradation that occurs in males as well. But that evidence of males in general, running hot, is well demonstrated, and it does bleed over into the night and cause those often sleep problems.

That’s some of the reason that some people will get fussy about sleeping together. A lot of it is about movement. Also snoring is a big concern with desiring a sleep divorce, or it’s a motivating factor, I should say.

Tim Ferriss: So we’ve talked about one direction. We’ve talked about how sleep affects sex. What about the other direction? Is sex helpful, deleterious to sleep quality? What are the factors if someone’s trying to give themselves the optimal dose of sex to improve sleep, if there is such a thing?

Dr. Matthew Walker: Yeah. And one should never state that that’s the reason you say, “Darling, could we just venture into the bedroom? Of course. But it’s because I’ve had really rough sleep the past couple of nights. Can you just like — please knock me out?”

Tim Ferriss: That’s a crowd pleaser.

Dr. Matthew Walker: Yeah. Isn’t it just — there’s a real divorce rather than a sleep one. But I think the evidence is actually favorable that when we survey couples, what we find is that sleep — although there’s a caveat here. Sex, as long as it’s associated with orgasm — and I’m not pointing to any one of the two sexes, maybe males. But please keep this in mind that sex, as long as it accomplishes orgasm, is associated with about 70 percent increase in reported sleep quality that following night, and people do fall asleep faster as a consequence. And we’re learning about the mechanisms, but I would say that it’s probably quite depressing to hear that news if you are, let’s say you are single, or you don’t have a partner, or your partner is away for a while. You don’t have to worry too much because it turns out that masturbation is a reasonable stand in. And what we’ve also discovered is that masturbation, again, as long as it’s associated with orgasm, produces a 47 percent increase in your sleep quality. And actually, it will decrease the speed with which you fall asleep by about 50 percent. And you’ll hear this a lot, some people will say they use it as a method when they’re struggling with sleep. They will actually masturbate to try to help their sleep. So masturbation is not as impactful as intercourse based on the data, but it’s a sizable benefit that rests in your hands, I guess. But it’s a nontrivial benefit.

It’s a playful topic of course, and we joke, but I do find it interesting regarding the biology. And we’ve tried to scratch the surface here and dig down. Firstly, what we found is that the benefit of sex with orgasm on sleep is hormonally related. But now, it seems to be that when women engage in intercourse that results in orgasm, there is an increase in a hormone called oxytocin, which I’m sure many people have heard of. Now to a lesser degree, that there is also an increase in men. But firstly, we know that oxytocin is a sleep-inducing molecule and you can inject this into the brains of different animals. We don’t do animal work, we do human work, but you can see that sleep induction benefit. The benefit in men seems to actually be about a different chemical called vasopressin. And although that story is just starting to emerge, it seems to be those two hormones. Oxytocin more so for females, vasopressin for males.

Tim Ferriss: So vasopressin, that’s interesting to me because vasopressin is, as I understand, an antidiuretic hormone sometimes given to adolescent bed wetters. Also, while what it’s prescribed as desmopressin, I suppose — this is maybe a topic for another time, but seems to have an impact on short-term memory, which is quite interesting to me. But how does vasopressin help sleep? Maybe it just keeps you asleep longer because you’re not inclined to get up and go to the bathroom. I don’t know. I mean that’s one of the reasons why it’s prescribed as desmopressin as well,

Dr. Matthew Walker: It’s possible, but it seems to have a sleep inducing mechanism and we don’t truly understand why — 

Tim Ferriss: Why?

Dr. Matthew Walker: — but we think that it’s perhaps working at two different levels of the brain. One is directly at the level of the brainstem itself, where you’re starting to shut down the wake promoting regions. I think we discussed that in the previous episode. Things like histamine or adrenaline, serotonin. So one component is working at the level of the brainstem. The second is working at a much smaller structure, but more in the middle of the brain called the hypothalamus, which is actually where we have what’s called the sleep wake switch. And it’s literally a flip flop device. And there is some signaling direction of vasopressin on that sleep switch within the hypothalamus itself too.

But right now, I think it’s pretty unclear as to exactly how those mechanisms unfold. But I do find them interesting because if we’re looking for novel sleep aids, all joking aside, then should we be thinking about combinations of oxytocin and vasopressin as novel sleep-inducing capacity. I think the second part of those two chemicals however, is also the other side of the coin, which is the nervous system itself. That when you are engaged in the act of sex, the fight or flight branch of the nervous system, what’s called the sympathetic nervous system, which is not that at all. It’s very agitating and aggravating. It actually should be called the three Fs branch, now I think about it. Which is the fight, the flight, and the fornication branch of the — 

Tim Ferriss: Good save, good save, good save.

Dr. Matthew Walker: — of the nervous system.

Tim Ferriss: Your Hugh Grant honorary degree has not been revoked. All right.

Dr. Matthew Walker: I was trying to come in there. But what’s interesting is that you cannot fall asleep when your sympathetic nervous system is switched on. And I’m sure you’ve had the experience. I’ve had this too, where you are that you are tired, you know that you are so sleepy and fatigued, but maybe it’s because you’ve just done a big event on stage and you’re just so wired. And it’s called the “wired but tired” phenomenon where you are desperately wanting sleep, but you can’t. The reason is because your sympathetic branch is still switched on.

But post coitally, what happens is that you go back to the opposite side, which is the parasympathetic, which is this quiescent, calming branch of the nervous system, and that is the royal road to better sleep. So it’s almost as though the orgasm removes the block of the fight or flight branch of the nervous system and pushes you into that relaxed autonomic state. And so I think that’s — how do we work that with new sleep inducing novel medications too?

Tim Ferriss: So a few things come to mind for me. Number one is, guys, this doesn’t mean you have free license to open your extremely bright blue light emitting laptop and watch a bunch of porn right before bed because that may stem some of the benefits. So you’re going to have to use that imagination instead of God knows what arms race you’re watching on PornHub. Second is, guys, buy a Hitachi Magic Wand. Get the wireless edition. You’ll thank me later. If you are in heteronormative relationship, that’s for your lady friend, and she will thank you as well.

Dr. Matthew Walker: I’m so wet behind the ears, I’m now — can we please link to it in the show notes so that I at least can click on the thing?

Tim Ferriss: I’m just going to edit that so that you just say, “I’m so wet.” And then I take out “behind the ears” and see what people come back with. They’ll be like, “Wow, that Matt Walker’s really taken a side road we didn’t expect.” Oh, God, I’m sorry to — 

Dr. Matthew Walker: “I knew that maybe he and Tim were friends, but…”

Tim Ferriss: I know I’m taking this down.

Dr. Matthew Walker: Yeah. Where’s that position in Austin for me at the university? I’m quick to jump from UC Berkeley. Anyway — sorry.

Tim Ferriss: So let’s talk about another, let’s say, aid, outside of the Hitachi Magic Wand and speed wank before bed — which I know I’m violating the roadmap that you and I discussed a bit, so I’m hopping ahead a little bit. But let’s talk about it because it’s on the mind. Melatonin. How would you suggest people think about melatonin?

Dr. Matthew Walker: If you look out there in terms of the silverback 500-pound gorilla of the sleep supplement world, it is melatonin. It commands a multi-billion dollar segment of the market, which is utterly stunning to me. Melatonin is not really going to be your sleep friend for a number of reasons. I think people don’t understand what melatonin does. Melatonin is a hormone, by the way. It’s sometimes called the hormone of darkness or the vampire hormone, just because it comes out at night. Doesn’t mean that you start biting into people’s necks. But it simply that it signals nighttime to the brain. And what that does is it regulates the timing of your sleep, but it doesn’t participate in the generation of sleep itself. And so you could think of melatonin like the starting official at a 100-meter Olympic race. That melatonin brings all of the races to the line and begins the race, but it doesn’t participate in the race itself. That’s a whole different set of chemicals.

So melatonin is potentially useful when you’re traveling between different time zones, but once you’re stable in a time zone, that evidence is very clear when we look across all of the studies and we gather them together in the same statistical bucket — and it’s called a meta-analysis approach. What you find is that melatonin will only increase the speed with which you fall asleep by 3.9 minutes, which is really not that different to placebo, and it only increases your sleep efficiency by just 2.2 percent, which is really not fantastic as a sleep aid. But it’s understandable when you then go back to what we were just describing as the mechanism, why would it improve the quality of your sleep if it’s there to help the timing rather than the generation of sleep itself? Does that make some sense, Tim?

Tim Ferriss: Yeah, it does. It does. And I think this is also a good place to talk about not just the minimal upside, because I would say there are people out there — and I’ve experienced this when traveling internationally. If you take a walloping dose, it can help put you down. So I would imagine the efficiency and the effect on reducing onset time is dose dependent on some level. So you can brute force it. And I have found it very helpful, say, going from one side of the planet to the other. However — 

Dr. Matthew Walker: Yeah, and I would use it too in those circumstances, that’s the only time.

Tim Ferriss: But there are taxes that you may pay. And it makes me think about — I don’t want to steal the mic here, but a conversation I had with someone, actually very smart researcher, probably 10 years ago. And he mentioned in passing that he took eight milligrams or 10 milligrams of melatonin every night. And I remember talking to him and saying — I’m no scientist, but my guess is that if you take something that is produced in the body, or something that is very similar, so you could have, say, luteinizing hormone and hCG, very comparable. And if you start exogenously, meaning from the outside in, providing your body with X, it is going to have a negative feedback loop and things are going to start to happen. So it doesn’t strike me just, again, starting from those principles that taking melatonin continuously eight milligrams a night would over the long term be a good idea. That was sort of my stance, and I’d love to know what are the downside possibilities.

Dr. Matthew Walker: You are absolutely right in your thinking. The body has a huge number of feedback loops, and when you start exogenously, meaning taking it from the outside and in the body, you can play with those feedback loops where you start to shut things down. And the concern with melatonin, even at five milligrams, or even three, and certainly at 10, what we would classify that is as a supraphysiological dose. Meaning that it’s a dose of a concentration that is maybe 10 times anything that your body would naturally release. So it is a whopping dose in that regard.

And by the way, you’ve got no idea whether it’s 10 milligrams or not. There was a study that looked at 30 different brands, and what they found was that based on what it said on the bottle versus what was actually inside of the capsules, it ranged from, I think, it was about 83 percent less to 478 percent more than what was stated on the bottle. Because at least in the US, it’s not FDA-approved. And just recently, maybe it was three, four weeks ago, there was a report demonstrating that melatonin overdoses that have been reported to the US Poison Control Center have risen by 530 percent over the last 10 years. And what’s especially concerning is where that bump is happening. It seems to be particularly in pediatric populations too. So we need to — 

Tim Ferriss: That bad?

Dr. Matthew Walker: Yeah, exactly. Keep that in mind. But coming back to your question, that is far too high of a dose, and the concern is about shutting down the brain’s feedback. That’s one of the taxes that you could pay. Some people have pushed back on social media and the internet to suggest — firstly, and I think they’re right, that melatonin overall in terms of its mortality risk profile is quite low. It seems to be a somewhat safe molecule in the sense of absolute death, but that’s obviously a very extreme threshold for you to use. People then also cite a study where they said if you dose for a high concentration for a long period of time, there was no change in the individual’s generation of melatonin itself. But if you look at that study, it’s actually a case study in a blind individual, and they were dosed with melatonin at high concentrations for, I think it was about was 37 days. So yeah, about five weeks.

And sure enough, by the end of that, when they withdrew the melatonin supplementation, the individual went back to producing the same amount of melatonin that they produced before. So you could argue from that perspective, no harm, no foul. The problem is that’s not how people use melatonin, that people are using it for six months, 12 months, five years. And therefore I don’t think we’ve got any scientific data to meaningfully tell the public that they should not have these concerns, in my humble opinion too. And the reason I say that — you can think about something like testosterone supplementation in males. You can use supplementation, and after three or four months if you stop, testosterone production from the testes themselves will start again. But there is a concern that has to be had between the physician and the male who wants that prescription that if you continue to take it long term, it may ultimately shut down the production of testosterone. And when you stop after long term use, six months, 12 months, you don’t go back to producing your own testosterone. Is that true of melatonin? We don’t know.

But the reason I also would caution people around melatonin, and I don’t mean to scaremonger. But firstly, there’s some really fascinating data in juvenile male rats where when you give high levels of melatonin, you get testicular atrophy, you get testicular shrinkage. So that is certainly a concern, especially now we’re seeing melatonin doses in pediatric populations. That’s a real big concern. We also know that high doses of melatonin will block the ability of your hippocampus to form new synapses. Hippocampus is a memory related center, and therefore it makes it more difficult to learn new information because you can’t form brain connections as well. So please keep that in mind. I do think though that there is — I said that melatonin as the sleep timing hormone. There is one study that I looked at where I think you could argue that melatonin has a sleep generating benefit above and beyond simply the timing of your sleep, which is that when you give it in somewhat high doses in rats, it’s thermoregulatory and it causes hypothermia. So not hypothermia to the degree of life concern, but basically it reduces core body temperature. And we know that you’ve got to drop your core body temperature to get to sleep. So I think melatonin, if it does have a sleep benefit, could be acting through this root of temperature and I think that’s fascinating for me at least.

Tim Ferriss: Few follow-up questions. So the study, you mentioned the case study with a blind person where I thought that was going — and keep in mind that I know just enough to be dangerous and throw around words that I probably shouldn’t — but if melatonin is, in sighted people, triggered in part by light signals or light cues, if you have a blind person — and again, I don’t know what role I immediately think of the superchiasmic nucleus, I think it is the — 

Dr. Matthew Walker: Suprachiasmatic nucleus.

Tim Ferriss: I always fuck that up. God damn it.

Dr. Matthew Walker: So close.

Tim Ferriss: Nothing ventured, nothing gained. How do you say it properly? I always screw that up.

Dr. Matthew Walker: Suprachiasmatic nucleus. And it refers to the chiasma, which is a Latin derivative term meaning crossing and it’s where your two optic nerves from your left and right eye meet and then cross over and reverse to the back of the brain. It’s right at that fulcrum of the cross, and it’s just above it. Hence supra meaning above, chiasma meaning the crossing and the nucleus, obviously. So suprachiasmatic nucleus.

Tim Ferriss: Supra — also as in supraphysiological. So I’ll just call it the SCN. So what my thinking was, well it’s really not apples to apples if you’re comparing a blind person to a sighted person, and it may be that their production of melatonin is less affected or maybe already handicapped to begin with in such a way that their processing of and recovery from melatonin administration is just completely different from a sighted person. I mean, that wouldn’t be shocking to me at all.

Dr. Matthew Walker: It’s a wonderful acumen. That’s exactly why we often will work with melatonin with these patients. Now it depends on the form of the nature of blindness. For example, if it’s blindness because, let’s say that you had damage to the back of the head and you damage your visual cortex and the eye itself, the retina is intact, the optic nerves are intact, but it’s the back of the brain where you’ve got that blindness disruption. That can happen there. That’s not necessarily a concern because the light signals are still at least coming down the optic nerves and hitting the suprachiasmatic nucleus, this 24-hour — and the suprachiasmatic nucleus, by the way, is where your circadian rhythm sits. It’s the master clock, the master 24-hour clock within the brain. You’ve got clocks all over the body, but that’s the one, it’s kind of one ring to rule them all. It’s like The Lord of the Rings. It’s one clock to rule them all. That’s the SCN.And that still gets light in people who have intact retina and intact optic nerves.

If you don’t, however, you don’t get the light signal to your suprachiasmatic nucleus, your brain gets confused about is it nighttime outside or is it daytime? And therefore sleep is very disrupted. They have actually what’s called a free running sleep system where they just run around the clock in terms of the circadian rhythm. It’s not regulated and set to the light dark cycle. Hence we use melatonin. But is that how normative is that case study? Firstly, it’s one person. Secondly, it’s in someone who has a deficit that already alters melatonin regulation. Again, I think it’s a fascinating study, but I’m not sure I put too much weight in it right now.

Tim Ferriss: Too much weight into a single case study.

Dr. Matthew Walker: Yeah, I know. I’m trying to be kind, but so I would say — 

Tim Ferriss: I mean, case studies are important, which is not to denigrate it in any way, but it’s easy to overinterpret or overapply something like that. Question then related to the — not to get too scientific, but the shrinking balls phenomenon observed in these juvenile rats. So I’m thinking of another thing you mentioned, which is say anabolic use or anabolic androgenic steroid use might be getting the AAS use, exogenous use. So it could be in the form of testosterone replacement cream. It could be injectable testosterone ate or whatever it might be. And if used for an extended period of time — and it doesn’t actually need to be that long. I mean, there are certainly anecdotal reports in case studies of people who even after what someone might consider a reasonably moderate cycle of say eight to 12 weeks, depending on the dosage, I know one person personally who had severely impaired testosterone production and libido for about nine months after a very short cycle of what I would consider moderate dosing of some of these androgens.

And the reason I bring that up is you have the testis axis, which is the hypothalamic pituitary gonadal axis, right?

Dr. Matthew Walker: Right. 

Tim Ferriss: Which is simply — and I’m fumbling around here, but you’ll see where I’m going at this. So if you interfere upstream or directly, you inhibit, as I understand, the light cells from producing any number of things and then you have this shrinking testicle phenomenon. How does melatonin — what is the plausible mechanism for that happening? Is it disrupting sleep architecture in a similar way that would be observed from too little sleep and therefore you see a decrease in testosterone? What is causing that testicle shrinkage?

Dr. Matthew Walker: No, the study or the studies really showed that the effects were directly there in the testes themselves. And it was — 

Tim Ferriss: Nasty.

Dr. Matthew Walker: Yeah, that it was directly altering the androgenic benefits that would normally happen during development, during adolescent development. And it was inhibiting that androgenic — and andro obviously being the sex hormones and genic being the promotion, the genesis. So it was inhibiting the normal development of the testes and therefore leading to a failure to promote them in terms of their size and development. I think they even have now done disease where they were showing that the seminal tubes themselves, the tubes for semen were also impaired as a consequence of high doses of melatonin as well. I could have that wrong, but that’s my recollection.

Tim Ferriss: In high doses, if we are looking at — since rats aren’t always little humans, but when we say high dose, are we are the sort of mgs per kgs, milligrams per kilogram comparable to what a human would be consuming if they are taking — let’s assume the dosing is accurate on the bottle just for the sake of simplicity — eight milligrams, 10 milligrams? Or would it be a human equivalent of someone who, say, being 160 pounds taking 160 milligrams of melatonin? Do you have any idea what the comparable would be?

Dr. Matthew Walker: It’s difficult to look at those ratios if you try to match the paper in part because of the way — 

Tim Ferriss: Administration.

Dr. Matthew Walker: — the administration, and because it’s direct administration rather than going through sort of hepatic clearance and the stomach and all of that stuff. So it’s going to be tricky, I think, to do the one-to-one transformation.

Certainly what we found with studies, if you are looking for a melatonin sleep benefit, there was one paper that demonstrated probably the optimal doses somewhere between about 0.3 to 0.5 milligrams of melatonin. Now, if you go onto the internet, it’s going to be very difficult for you to get something even as low as one milligram. And here we’re talking about maybe half of that dose of concentration. Most — you’re lucky if you can find three milligrams. Most will be five milligrams or 10 milligrams. That’s the whopping dose that we’re we’re talking about here.

Tim Ferriss: Yeah. Oh, man, what a mess. Humans, man, we make such a mess. It’s just like, I remember when they’re like, carrots are good for this. Let’s isolate beta carotene and megadose that. Oops. Yeah, sorry about that. It’s just over and over again.

So if we could keep on the sort of unconventional, let’s just say tips/perspective side of things if you don’t mind, I would love to talk about, and this is something that I haven’t discussed with you at any length, the art of minimizing sleep time. And this may tie into CBTI, which I really don’t know that much about. But I, like a lot of people I think have made the error, although it doesn’t feel like an error of getting into bed, and even if my sleep onset takes an hour, hour and a half because maybe I have that tired and wired feeling, which a lot of people do, a lot of veterans, people with PTSD suffer from this overly activated sympathetic nervous system, which I do a lot, and I’ll just stay in bed. Even if it takes me three hours to get to sleep, I will often just kind of sit there and try to meditate my way into oblivion, which doesn’t always work very well. So what’s the counter approach?

Dr. Matthew Walker: Yeah, so I think one of the sort of conventional tips for sleep, you can find all over the internet and idiots like me, you can hear speaking about the five tips of better sleep hygiene. And there’s very good evidence for why those are sensible things to put in place.

But what about the unconventional? And one of the unconventional components is to limit your sleep time. As you said, there is the principle — the principle treatment for insomnia should not be the first line defense of sleeping pills that we discussed in the last episode. The current recommendation is something called cognitive behavioral therapy for insomnia, or CBTI. And as you can tell by the term, it works on two things, cognitive things, in other words, your thoughts and your beliefs about sleep and then your behaviors. What are you not doing that you should do to help your sleep and what are you doing that you shouldn’t be doing and you should stop doing to help your sleep? And that’s the CBTI component.

Probably if you look across the studies and CBTI has a number of different features in this treatment, this therapy approach. But one of the most potent tools in the box of the CBTI therapist is what we call sleep restriction therapy, which sounds paradoxical. I come or you come to me and let’s say I’m your sleep clinician, and you say, “I am not sleeping well. I’m in bed for about eight hours, but I think I only maybe sleep for four, four and a half hours. I’m just not getting enough sleep. Can you help me?” And my response to you is, “Excellent. I’ve got a great treatment for you. It’s called sleep restriction therapy.” And you hear the kind of the record scratch and you say, “Hang on a second, I just told you I’m not getting enough sleep and you are telling me we’re going to restrict my sleep.”

It’s actually a poorly termed phrase. It should really be called bedtime restriction therapy. And it works in the following way that right now, if you take that example, you are in bed for eight hours and you’re sleeping for four hours, you have a miserable sleep efficiency. So you have a sleep efficiency of 50 percent. Half of the amount of time that you’re in bed, you’re awake, half the time you’re asleep. We want to see that around about 85 or greater in terms of your sleep efficiency. That’s what we think is healthy. And so rather than actually having you stay in bed for any longer, we do the opposite and we use the biology of your brain and something called sleep pressure.

So from the moment that both you and I woke up, we’ve been building up a chemical that we’ve sort of discussed with regarding caffeine, which was adenosine. And the more adenosine builds up the sleepier and sleepier you feel, and the longer that you are awake, the heavier that weight of sleepiness will be weighing you down. So just take the extreme of let’s say you pull an all-nighter or you’re awake for 36 hours. Imagine how tired you are at that point when you get into bed that following night. It’s almost as though nothing’s going to stop you. Earthquakes, wildfires, you’re just going to get into bed and you’re going to be knocked out. Why? Because you’ve just got so much sleepiness built up, so much adenosine that hasn’t been removed.

So we do a diluted version of that in CBTI with sleep restriction therapy where we say, okay, you’re going to bed — just for argument’s sake at midnight and you’re waking up at 8:00. Now what I want you to do is actually compress that window of time and I want you to go to bed not at midnight, but now push it — go to 2:00 a.m. or 2:30 a.m. or let’s say 3:00 a.m. but you still wake up at the same time. So where we restrict your sleep is not by having you wake up any earlier, which is kind of miserable. And most people, people feel it’s easier to go to bed later than wake up any earlier.

So we start there, we limit the amount of time that you are in bed and we restrict it down to maybe six hours or five hours, and the next day you’re going to feel miserable. You’ve only been in bed for five hours. But what happens is that as long as you commit to it and it has to be committed and you have to work with someone who’s going to motivate you, and it is hard, but it works. And after the second night of being in bed for five hours, you’ve been awake for longer. So now you’ve been awake for 19 hours during the day and you’re only in bed assuming for five hours. And that increase in your adenosine because you’re awake now for 19 hours straight for one day, for a second day, for a third day, it all starts to accumulate.

And then at one point, maybe, and it depends on the patient, let’s say about four or five days after that, they get into bed at 2:30 a.m. or 3:00 a.m. and then the next thing that they remember is their alarm going off at 8:00 a.m., and for the first time ever, they have slept all the way through from front to back. Now in that example, I’ve restricted their bedtime by three hours and they’re now sleeping a solid five hours. But remember that’s better than where they were. They were in bed for eight hours and they were only sleeping for four hours. So I’ve added an extra hour and they’re in bed for less time.

And then gradually what we do is we start to back that up. Once you’re stable and your sleep efficiency is 85, 90 percent, then we’ll say, okay, now go to bed at 2:00 a.m. and then now let’s go to bed at 1:30 a.m. and now let’s try 1:00 a.m. and gradually we back it off. And essentially it’s like hitting the reset button on your Wi-Fi router. You are retraining the sleep system. And in doing so, you can start to get people’s confidence renewed because that’s a big problem with insomnia.

Tim Ferriss: I was going to say it sounds like more than anything — well, I shouldn’t say that. Who the hell am I? But it seems like principle among the reasons that would work is that you are resetting sleep-related anxiety.

Dr. Matthew Walker: A hundred percent. Because when you are suffering from insomnia, and I’ve had my bouts too, and I know that you’ve spoken publicly about struggles before, you go into the bedroom and the bed just looks like the enemy and you have lost all confidence in your ability to sleep. And at that point your sleep controls you. But by way of CBTI and sleep restriction therapy, you turn the tables. Now, you control your sleep, not your sleep controlling you and you regain confidence. That is a huge win. I can’t tell you how big that is for people with insomnia. It’s a terrible fear when they go into the bedroom. They just convince themselves “It’s not going to be my night.” So does that sort of help? I know it’s a long explanation.

Tim Ferriss: It does help.

Dr. Matthew Walker: Yeah. And it’s a little bit like working out. If I go to the gym for an hour, and for the most part I’m probably only working out for maybe 40 or 30 minutes because I’m looking my phone, I’m chatting to people checking social media, whatever it is. And so you’re only really working out for 40 of those minutes. It’s not an efficient workout. But now my gym says, “I’m sorry, we’re limiting it to 30 minutes every day. You got no more time than that.” After a couple of days, I don’t have the choice. I’m thinking I’m not getting my workouts in. So I put my phone on silent, turn it off, and I just go in there and I hit the gym hard and I work out for 30 minutes straight. My efficiency is improved.

Tim Ferriss: So let’s segue and I’ll let you choose how you want to bridge things to lucid dreaming, and we can do it in a few steps if necessary. In part because when I reflect on the periods of best sleep, let’s just say past adolescence or early adolescence, some of my best periods of sleep — and I could unpack what I mean by best — but easiest, lowest stress periods have been when I have focused on inducing lucidity. Because instead of dreading sleep, I end up looking forward to sleep and it turned everything on its head. Now the downside is, we might get to this, there’s quite a bit of training required and things need to be a bit regimented in my experience. But how would you like to move to lucid dreaming, including a definition of lucid dreaming?

Dr. Matthew Walker: I think perhaps what we could do is start with what basic dreaming is and what it is perhaps psychologically, neurologically from the level of the brain because neurological is important when we try to understand what lucid dream, what lucid dreaming is and how it’s different to standard dreaming. And we can also touch on the functional benefits of dreaming, but maybe we could leave that aside. I think we spoke a little bit about that before in the first episode.

But from a psychological level, dreaming, I mean, it’s pretty ridiculous when you think about it because last night, you and I, when we went to sleep and we started dreaming, we became completely psychotic. And before you reject that sort of diagnosis of my nighttime psychosis, I’ll give you five good reasons. When we dream, we start to see things which are not there. So you are hallucinating. You also believe things that couldn’t possibly be true, so you’re delusional. You get very confused about time and place and sometimes also person as well. So you’re suffering from disorientation. You often have these wildly pendulum-like almost fluctuations in your emotions. And it’s what psychiatrists will call being affectively labile or emotionally labile. And then how great you and I both woke up this morning and we forgot most if not all of that dream experience. So we’re suffering from amnesia.

And if you were to experience any one of those five things while you’re awake, you probably would be seeking some form of psychiatric intervention. But for reasons that we’re now only starting to understand when it comes to the functions of dreaming, it’s a perfectly normal biological and psychological process.

The biological process is utterly interesting. We and others have done studies where we’ve been putting people inside of brain scanners and we let them go through the different stages of sleep and we let them go into REM sleep. Now dreaming, if you use a loose definition, which is the report of any mental activity upon awakening. If you use that loose definition, you dream in almost every stage of sleep. But what most people think of when you say dreaming are REM sleep dreams. Those are the emotional, the narrative, the bizarre, the strange. That’s really the state from which you dream. And when we look at that sleep stage inside of the MRI scanner, firstly vast swaths of the visual cortex start lighting up in your brain. The motor regions of the brain erupt in activity. Emotional centers of the brain become active as well as memory centers of the brain.

And in fact, some parts of your brain are up to 30 percent more active when you’re in dream sleep than when you’re awake, which is stunning to me because we often think of sleep as just this passive unconscious state. But metabolically from the brain perspective, it’s wild.

But the freakish part is what happens to another region of your brain called the prefrontal cortex, and particularly the left and the right side, which sits just above your eyes. And it’s particularly a region called the dorsal lateral prefrontal cortex, left and right side of the frontal lobe. That part of the brain, normally when it’s active, acts like the CEO of the brain that makes high level sort of executive top-down control decisions. And it allows you to have not just rational decisions but volitional decisions. In other words, you are choosing to make that choice and you’re choosing to do that action. That’s part of the prefrontal cortex job.

That part of the brain goes offline when we go into REM sleep. Your dorsal lateral prefrontal cortex doesn’t erupt with activity like many of these other regions. It is suppressed in its activity. And that I think is our current explanation as to why your dreams are so visual, so motoric, filled with past memories, also just highly emotional. But they’re utterly bizarre, utterly erratic, and you have no volitional control. The prison guards have left the building and the prisoners are running amuck. Your prefrontal cortex is down. And so that’s one of the fascinating parts of dream sleep neurologically — as well as the body by the way.

I think we probably didn’t discuss this before, but when you go into dream sleep, your brain paralyzes your body. You are completely limp. So if I were to come into the bedroom and just pick you up during REM sleep, you would be like a ragdoll. All of your skeletal muscles are inhibited. And people don’t need to worry, by the way. Your involuntary skeletal muscles that control your respiration and your heart, they’re not affected, but all of your voluntary muscles are because your brainstem, which is where the REM and non-REM mechanisms play out. Not only does it beam an activating signal up into the dreaming brain, it sends one down the spinal cord and it paralyzes what’s called the alpha motor neurons of the spinal cord that control your voluntary skeletal muscles.

So you are locked into a physical incarceration during REM sleep, during dream sleep, which by the way explains something called REM sleep paralysis upon awakening and adequately explains most alien abductions. But we don’t need to go there. We can always move on to what’s different about dreaming when it comes to lucidity or just pause there and go into anything that comes to mind.

Tim Ferriss: No, let’s jump into lucid dreaming. I’m ready. I’m done now. And I do want to talk about tracking of time or perception of time at some point. But I think we can do that vis-à-vis lucid dreaming, because I have some yes questions, so I’ll get there. But let’s jump into lucid dreaming.

Dr. Matthew Walker: Yeah, lucid dreaming. It used to be a complete charlatan science back in the ’60s and the ’70s. To suggest that you could gain control over a normally non-volitional process only added insult to the idiotic nature of this thing called sleep and dreaming by itself. And now you’re telling me, okay, we’ve got these things called dreams, and also you claim to be able to control them and do whatever you like in them. Really? Show me some good science.

But now we have some exquisite science and it’s not even debated anymore. It’s not a charlatan science. And the first experiments actually come back to our first topic, which was sleep and sex. The first experiments used orgasm and ejaculation as the test. So with a lucid dreamer, when they are asleep, just like you and I, when we’re not lucid dreaming, they are paralyzed. So they’ve got no good way to tell you, “Okay, I’m now lucid,” and they have no way to tell you what I’m dreaming about and what’s happening, except that they do, which is their eyes.

Because one of the two muscle groups that is spurred from the voluntary skeletal paralysis of your muscles are the extraocular muscles that move your eyes up and down and left. And that’s why by the way, you still have rapid eye movements during REM sleep, because those muscles are not inhibited. So we can now generate essentially a language between me, the experimenter, and you, the lucid dreamer, which is like an ocular Morse code. And you can be telling me, using predefined eye movement instructions, what’s going on.

So at the moment you become lucid, you’ve gone into dream sleep, and I can see that in the next door sleep control center. And then all of a sudden I see, based on your eye movement traces that I’m measuring, you do three deliberate flicks to the left. And that’s your signal to me that “Me, the participant, I’m now lucid.” Okay, great. Now then you’re going to do two big circular movements to the right. And that’s you saying, “In my dream, I’m now clenching my right hand and then moving your eyes circular to the left. That’s me moving my left hand.” And so you can be telling me every time that you’re doing something in your dream what it is that you’re doing, which is just — I mean, could you imagine?

Tim Ferriss: And then if you’re like, “If you like that trick, now watch me ejaculate!”

Dr. Matthew Walker: Well, that was exactly what they did. So then they said, okay, you claim to be able to — because when you control — lucid dreaming, by the way, the definition, is just that you are aware that you are dreaming as you are dreaming. That’s our basic scientific definition. But what most people in the lay public think of as lucid dreaming is not just that you know that you’re dreaming, you take control over your dreams. And of course, if you can control your dreams, one of the things that people enjoy doing is having sex and having an orgasm.

Tim Ferriss: That’s all they’re going to do. That’s all they’re going to do.

Dr. Matthew Walker: Yeah, exactly.

Tim Ferriss: Orgy all — everywhere.

Dr. Matthew Walker: It was the original dreamscape pornography. Forget PornHub, you just had to lucid dream.

Tim Ferriss: It’s a heavier lift, but yeah.

Dr. Matthew Walker: It is. But I could argue it’s well worth it. So we’ve got these experiments now — and by the way, we’ve done imaging studies that are less messy for the experimenter to — but I should come explain that by the way. People would then say, “Okay, I’m now starting to have sex and I’m now just about to have an orgasm.” And then they would say, “I’ve just had my orgasm.” And you can go into the room and sure enough, with males especially, you’ve got proof positive data that what they said was real. And hence, you’ve just scientifically proven lucid dreaming is great.

We’ve got much more sophisticated MRI scanning methods now, and I won’t bore you with the studies, but it’s very clear that we know that lucid dreaming is real.

The next question then was how do people lucid dream? What is the underlying neural mechanism? And this comes back to the prefrontal cortex and those dorsal lateral prefrontal parts of the brain, which are the volitional control centers which go offline. What we found is that activity, both the electrical activity and also when you put people in scanners, the imaging activity in those regions, starts to ramp back up again, as if when you become lucid, you regain your rational logical control over the dream state. And so the prefrontal cortex gives you that capacity to take back what you lost, which is volition.

There was a study recently, however, that I think did a pretty good job to say that may not be the case, that some of those are results are confounded by the method of the analysis and the method of the recording. So I think it’s — the jury is still a little bit out, but even in that study, they demonstrated that there’s something about their brainwaves that is radically different at that fulcrum point where they shift from going from non-lucid dreaming to lucid dreaming. It’s not a question of if, it’s just how.

Tim Ferriss: What is the jury still out on? I’m sorry, I missed that.

Dr. Matthew Walker: So the jury is still out on this idea that the electrical bursting brainwave activity is — it comes back online over the prefrontal cortex. And what they were finding is that it’s potentially an artifact of the eye movements that start to happen. So the eye movements, when you’re moving those muscles, those extraocular muscles, you move muscles using electrical impulses. And those electrical impulses that are coming from the eye will also bleed up into the brain. And when you get all of this frenetic eye movement, it starts to masquerade as if it’s the prefrontal cortex which sits directly above them as getting reengaged. And hence, when you control for that, you don’t see as powerful an argument for the re-engagement of the prefrontal cortex.

Tim Ferriss: What is your personal experience, if any, with lucid dreaming?

Dr. Matthew Walker: Unfortunately, I am not a common lucid dreamer. It’s happened probably about two or three times in my life. And when it’s happened, it’s immensely pleasurable. Have I tried to curate it, develop it, and use different techniques? And we can speak about the current techniques that are out there in the science. I have not chosen to do that. And it’s not necessarily because I see in the science anything to be worried about. I can steel man both sides of that argument.

We know that only about 10 to 20 percent of the population are natural lucid dreamers. And you could argue from an evolutionary standpoint that if lucid dreaming is so adaptive, so beneficial to us as Homo sapiens, then the reverse would be true, that Mother  Nature would’ve heavily selected it, and 80 to 90 percent of the population would be lucid dreamers. But I can push back on my own argument because there’s a desperate flaw in that logic. That argument assumes that we’ve stopped evolving. And we haven’t, right? So maybe that 10 to 20 percent of natural lucid dreamers are the forefront of hominid evolution and we don’t need to be worried about AI — we need to be worried about the lucid dreamers becoming the next super race of humanity. So I wrestle between those two, but if it’s that volume though, that 80 to 90 percent of people don’t naturally do it at this stage after 3.X million years of evolution of hominid development. My sense is that do I think that I understand better than Mother Nature’s blueprint exactly what I should be serving up in my dreams at night to get all of the benefits of dreams. And, by the way, we know that dreaming, above and beyond REM sleep itself, serves a number of key different functions like emotional therapy and emotional first aid. It supports creativity. And I’ve worried myself, is it hubris for me to think that I should then take the reins and get into the driver’s cockpit and start steering the vehicle, rather than just allowing whatever Mother Nature thinks should happen for me?

I don’t know. The only other strike against lucid dreaming, and I don’t think it’s a big one and I don’t think it’s anything to be worried about, when you survey people and when we’ve examined people who claim to be lucid dreamers, on a night after lucid dreaming, they typically report that their sleep is less restorative and less refreshing. They find it to be, perhaps, more mentally fatiguing, but I don’t think that’s really a big — 

Tim Ferriss: The second night? The subsequent night of sleep?

Dr. Matthew Walker: No, sorry. The next morning when they wake up after — 

Tim Ferriss: Oh, I understand.

Dr. Matthew Walker: — the night when they have had lucid dreaming they find that it was more fatiguing, perhaps because it’s more effortful because you’re engaging the prefrontal cortex. That’s one argument, but I don’t think that’s a particularly good argument to say that if you are a lucid dreamer you need to be worried or if you want to lucid dream you should not engage in some of the different methods that we’ve developed to improve it.

Tim Ferriss: I’m curious what the state of the art is from a scientific perspective, because people may hear the term lucid dreaming and think that it is a relativity new construct/exercise of the human mind, but that’s not true at all. I mean, at least for thousands of years in Tibetan practices and elsewhere — 

Dr. Matthew Walker: Exactly.

Tim Ferriss: — there have been elaborate descriptions of training and philosophical and cosmological implications of this type of sleep engineering, let’s call it. What are the predominant methods of or for inducing lucidity in these studies? Or that you’ve seen covered in the literature? I’m very curious.

Dr. Matthew Walker: Yeah, right now in terms of the science, we probably have two methods that have been put out there that have some degree of validity to them. Although, I would say that when you look at each one of the papers, the statistical robustness, in terms of the reliability of these things, it’s not especially high. I mean, some of these techniques do gain statistical significance, meaning that when you try them, it does significantly, from a statistical perspective, increase your likelihood of lucid dreaming. The first one, it’s called the MILD method for short, but it stands for the Mnemonic Induction of Lucid Dreaming, M-I-L-D method. And, essentially, it’s pretty simple that you create a conscious and very deliberate intention to remember that you’re dreaming and usually this is pre-bed, that you’re lying there before you go to sleep and you start repeating this intention, “I am going to deliberately remember that I am dreaming as I’m dreaming.”

And you keep doing that, night after night, over and over again, and it sounds hokey, it sounds really quite science L-I-T-E, lite. But the evidence is suggesting, it’s in favor. I think the other one that’s probably more popular is called the reality testing method and, oh, gosh, it was popularized in a — at least I think it was popularized — 

Tim Ferriss: Stephen LaBerge?

Dr. Matthew Walker: No. Well, so Stephen LaBerge was a fascinating researcher who was working here in the Bay Area in the 1980s and ’90s who probably was really the pioneer of modern day lucid dreaming. And then, at some point, he was doing academic really interesting scientific studies and then he moved away and he developed his own Lucidity Institute and sort of was selling CDs how to do that. So I think it went off in a slightly strange direction, and I don’t know what came of him. But the reality testing method actually came to fruition, on many people’s radars, with a brilliant movie called Waking Life by Richard Linklater. Have you seen this?

Tim Ferriss: It’s great. Yeah.

Dr. Matthew Walker: And maybe we can link to it in the show notes. If people haven’t watched it, don’t worry if you’re not interested in lucid dreaming, yes, the movie revolves around lucid dreaming, but the philosophy and the conversations will blow your mind. It is one my favorite — 

Tim Ferriss: And the visual treatment of the movie — 

Dr. Matthew Walker: Oh, is so — 

Tim Ferriss: — is perfect.

Dr. Matthew Walker: — clever. Isn’t it genius? And maybe we won’t spoil it for people who haven’t seen it. But the idea of the reality testing method is that during the waking day, you start to test reality, in a way that you don’t normally do. So let’s say that I would walk over to the table that I’m sitting next to here and I press my hand down on the table and the table is resisting my hand, just like the waking laws of physics would predict. Or I go over to the wall and I switch on the light switch, do the lights go on? And when I turn them off, do they go off? And hence, I understand that I’m probably in conscious waking reality. And you start doing this throughout your entire waking day to the point where it becomes a reflexive habit, and then the hope is that that habit bleeds through into your dreaming life from your waking life and you start to do the same reality testing in dreams. And then, all of a sudden I press my hand down on the table and it moves all the way through the table to the other side. And at that point I think, “Oh, the jig is up. I’m not awake. I’m dreaming,” and then you gain lucidity. Does that sort of — 

Tim Ferriss: Yeah, yeah.

Dr. Matthew Walker: — make some sense?

Tim Ferriss: Oh, it does. Actually, if you don’t mind me just — because I don’t think I’ve discussed this at any real length in any podcast, but this was a very strong focus of mine for a part of the last two years of high school. And then, I revisited it a few years later in college, and one might ask, “If you enjoy it so much, why the break?” And the break is because there’s training involved and I do suggest, this is an oldie but goodie, I’m sure there are, actually I know there are many, many, many books that have been published since, but Exploring the World of Lucid Dreaming by Stephen LaBerge. B-E-R-G-E. I’m probably mispronouncing the last name because I can’t speak French. But that book lays out the MILD technique that you mentioned and the reality testing. And I love to just give folks an idea, perhaps a few stories, and these are, yes, anecdotal, and of one. But I hope them to be, perhaps, inspiring in a sense.

So number one, I do not count myself among the people who are natural lucid dreamers, at all. I think most people have had the experience of lucid dreaming. “Oh, my god, I became conscious. I was dreaming and then I immediately woke up or went back into non-lucid dreaming.” Most people have had that experience, and I’d had that experience who knows, much like you, two or three times scattered over a very long period of time. But then, I read Stephen’s book and step one is practicing dream recall and putting together a dream journal. And there are a number of reasons for this, but one of the reasons is to identify good candidates, recurring patterns, that you can use as cues for your reality testing in waking life.

So, for instance, if you identify and your dream recall improves dramatically when you begin to journal in this way, immediately upon waking. You can’t check your phone, you can’t brush your teeth, you need to just roll over and immediately do this. And I do not think voice memo works nearly as well, because you’ll go back and you’ll reread the skeleton outline of fragments and that will prompt further recollection and you can fill in the blanks and that is a productive way of approaching it. You might identify that you walk through many doorways, for instance, or for whatever reason you end up in areas where you see grass or perhaps you look at your watch often in dreams, at which point you would identify those as candidates for this reality testing that you were referring to.

Or you can simply have an alarm, after you’ve started doing this dream recall, and at random points in the day, you have to do a reality test. Let’s give a couple of recommendations for folks. The first is if the reality test is hard to precisely convincingly test, it may not translate to dreams. So what I mean by that is, a lot of folks, when they’re starting this will say, “Well, I will try to fly.” And yes, you can fly in dreams, and I wasn’t kidding earlier when I said that people just go complete nymphomaniac. Generally, when people first gain the ability to intermittently induce lucidity, they’re just fucking everything and they’re flying everywhere. Those are the two things that everybody does. And that’s fine. But if, during your waking life, it’s like you have lunch and then the alarm goes off and you’re like, “Let me reality test.” How are you really going to attempt to fly in a convincing, compelling way?

But there are other options. For instance, and who knows, science can be expensive and who knows if these studies will ever get done or how they would even be done? But what I think experienced lucid dreamers will probably corroborate it that if you look at a pattern, let’s just say you have long tiles that have one orientation in a restaurant and you look away from them and look back at them, in reality, they stay the same. In a dream state, they very often, almost always reorient, because your mind is reconstructing that pattern, if that makes sense. And similarly, if you look at, say, a digital clock read out, something like that, the numbers will not be the same, the time will change.

And just for the practical applications here, yeah, you can have fun doing stuff, but at the end of high school I was going to be competing at a national-level in wrestling and so I would actually train with this coach from Oklahoma, John Smith, who’d I’d never met, still haven’t ever met, and I would actually do drilling in lucid dreams and, again, and of one, who knows? But I really seemed to discern a translation of that added practice time to the in-world practice, so to speak. So it’s a fascinating experience, I encourage everybody to try it out, but it is a commitment. It’s quite a commitment.

Dr. Matthew Walker: It is.

Tim Ferriss: It’s kind of like if you want to control your anger and you want to have a pattern interrupt and you need to develop that over time and to take something that is subconscious and make it conscious does take some time.

Dr. Matthew Walker: And I think that it’s fascinating, that last part that you said where when you were working with the coach that you truly, actually never worked with, but you saw it translate to the mat in the waking, real world. I think it fits very well with the idea of one of the functions of dreaming, which is this notion of abstract creativity, of problem solving. And we know that it’s during the dream state, it’s during deep non-REM sleep when we take individual memories that we’ve been learning and we cement them and we essentially hit the save button on them and we sort of concretize them in the neural architecture of the brain. But it’s during dream sleep that we take those newly, freshly minted memories and we start to interconnect and associate them with this vast catalog of previous knowledge that we have, so that you start to divine solutions to previously impenetrable problems, and the reason that happens is not because the dreaming brain is designed to build the obvious connections, it seems to do a Google search gone wrong, where it takes the new information, it inserts it and it immediately puts you to page 20.

So maybe I type in “The Tim Ferriss Show” and it takes me immediately to some field hockey game in Utah. And I think, “Hang on a second, how on Earth is that related?” But if I look, there is a distant. non-obvious connection, and this is what the dreaming brain and perhaps the lucid dreaming brain is particularly good at. It starts to fuse things together that shouldn’t normally go together, but when they do, cause marked advances in evolutionary fitness and it’s the biological basis of creativity. And so, I think what’s happening with that description that you mentioned, is that you’re waking up in terms of your skills, your motor skills, but also happens with knowledge, with a revised mind wide web of associations. It’s almost like informational alchemy that happens at night, and that’s why you can have these remarkable stories of people solving problems and coming up with incredible creative solutions and wonderful pieces of art and music and literature have all been inspired by way of dream creative insight.

And I think that’s why, perhaps, in part why you were feeling good about that benefit, is there are certain ways that you were performing skills and movements that you just couldn’t see when you’re awake, but when you go into the dream state and you force that to be on the menu of the dreaming digestion at night, then all of a sudden the dreaming brain was taking what you were learning and coming up with these novel, new insights. So I think it fits very well with what we know about one of the functions of dreaming, and it’s the reason that you’ve probably never been told to stay awake on a problem.

Tim Ferriss: Yeah, and I have not experienced the subsequent fatigue, which I think would’ve be, at least for me, very obvious, because I was training every day. And so, I think I would’ve subjectively noticed a decrease in performance. And I will just put a call out to the audience, if anyone out there is aware of someone who is the heir apparent or maybe the version two, version three or not, but of Stephen LaBerge, but somebody who is really taking lucid dreaming seriously, the different techniques for induction, perhaps, looking at the interplay of sleep, nutrition, other variables on inducing lucidity, please let me know on Twitter @tferriss. T-F-E-R-R-I-S-S, because I am deeply interested in this. And I remember back in the day when I was at school, I mean, this was in the ’90s, but some of Stephen’s acolytes were experimenting with things like — actually I was experimenting with huperzine A, but others were experimenting with galantamine and all these various supplements in the hopes that they would increase the frequency of inducing lucidity.

Dr. Matthew Walker: And there are some devices out there right now where people have sort of tried to have these ocular devices where they start to sort of flash lights into the eyes, and the reason that they use the ocular device is that the device itself can measure some parts of the brainwave activity, it can measure the eye movements, it senses when you go into dream sleep, and then it begins the flashing and the hope is that that flashing is an instigating trigger to build lucidity and make you aware that you’re dreaming. I’ve seen no data on how effective those are scientifically. But people are trying to take this to the next level. People have played around with compounds, they’re now playing around with technology.

Tim Ferriss: Yeah. So I’m going to give some further unsolicited thoughts that will, no doubt, just be very bothersome, because they’re not based on any data to speak of, other than my personal experience and also having read a number of books and different reports and gone on all these crazy forums, but experientially, and this could be pure placebo effect, but for most folks, when they realize they’re dreaming it’s like, “Oh, my god, I’m dreaming,” and then they snap right out of it. Either they wake up or they go right back into normal REM sleep, let’s just say. For whatever reason, looking at your hands or spinning, attempting to spin, like just spin in place much like you would physically, seems to help extend the session of lucidity, so to speak. Again, no studies to cite, no hard data to point to, but for people who want to screw around with it, there you go. It’s free advice, maybe worth what you pay for it.

I would love to, if we could go from here, perhaps, to segue to learning and memory and I know that you’re very deeply familiar with research as it relates to sleep, different phases of sleep, and various aspects of cognition, including memory. If one wanted to optimize for learning, now there are different types of learning, right? You could have procedural knowledge, like riding a bike of skill acquisition, like in my case, the wrestling. You could have declarative knowledge, more data-driven, memorizing Chinese characters is one that I’ve thought about a lot. How would you suggest people think about sleep and are there ways to optimize for learning or skill acquisition, aside from ensuring that your sleep is just not broken in some fundamental way?

Dr. Matthew Walker: I think what we’ve started to understand is that different stages of sleep do different things for different systems of memory at different times of night. So yes, the story is simple that you need sleep for learning and memory, but there is evidence that we can pattern match what type of things that you’re learning with a particular stage of sleep, if you wanted to try to dial it up. If we were so replete as scientist to have dials like a mixing deck where we could instantly say, “Okay, tonight you want more stage two non-REM sleep or you want more spindles, you want more deep sleep.” I mean, we’re getting there with brain stimulation, but it’s not quite there yet.

Tim Ferriss: The Deadmau5 DJ of sleep cocktails.

Dr. Matthew Walker: Exactly. Yeah, yeah. Maybe I should grab that Twitter handle already. But certainly what we know from the bigger perspective is that, firstly, you’ve got to get sleep before learning to prepare your brain for the initial act of imprinting and learning new information. And we’ve done some studies where we’ve deprived people of sleep and that night of deprivation, should you pull the all-nighter? Is it a wise idea? And the answer is no, because you’re about 20 to 40 percent deficient in your learning ability when you have not been getting sufficient sleep, which I do think is interesting when you consider what’s happening to sleep in our education populations right now, but I can put that aside. We also know why that’s the case. We did a study where we were looking at the brain trying to learn information with and without sleep inside an MRI scanner and there’s a structure that we’ve spoken about before called the hippocampus, which sits on the left and the right side of your brain and it’s almost like the inbox for memory, the informational inbox, that it grabs new memories. And when you don’t have sleep, that hippocampal structure, it’s almost like it becomes waterlogged, as it were, and you can’t — 

Tim Ferriss: Doesn’t sound good.

Dr. Matthew Walker: — absorb new information. No. Well, coming back to inbox analogy, I suppose, it’s almost like the inbox is full and you just start bouncing those incoming mails, you don’t commit the experience to memory, because what we discovered is that the hippocampus is shut down. And so, no wonder you can’t imprint that new information. We also found that if you want to reverse that trend and say, “How can I increase my learning capacity?” we did a nap study during the day and what we found is that it’s not just sleep, but it’s a particular bursting electrical brainwave called a sleep spindle, and the more of those sleep spindles that you are having, the greater the restoration of your learning ability. So the way we did the study, we took a group of people and we had them try and learn a whole set of information at midday, and then we brought them back and then at 6:00 pm we had them learn an additional new set of information.

And so we could simply compare what’s your learning capacity at time point one versus time point two. But then, half of the subjects had a nap in the middle of that six-hour period, the others did not nap, they remained awake. And there was a deviation, there was a separation such that those people who napped, they actually had a restoration of their learning ability. Those people that didn’t had a deterioration in their learning ability. And the greater the number of spindles during the nap, the sleep spindles that happen during what we call non-rapid eye movement sleep, the greater the refreshment and the recuperation of their learning ability.

Tim Ferriss: How long were the naps?

Dr. Matthew Walker: Yeah, so the naps there were 90 minutes in duration. Now, I wouldn’t recommend that for most people and I’ll sort of come back to why, but — 

Tim Ferriss: Is that an ultradian rhythm or is that a bullshit term?

Dr. Matthew Walker: Yeah. I mean, you were close with suprachiasmatic, and you’re bang on with the ultradian. So ultradian simply means it’s shorter than a day and circadian, when we describe it, it means approximately or around a day’s length. Ultradian, shorter than a day. And yes, in human beings, our sleep cycle going from non-REM to REM, which we repeat, is every 90 minutes. Now, that’s in us human beings. It’s different across different species. Our sleep cycle is actually quite long relative to others. For example, birds may just have a non-REM to REM cycle of about two minutes, which is very, very short. They flip back and forth. Us, 90 minutes. And so, usually when we do these nap studies, we give the brain the opportunity to cycle through both non-REM and REM, so then we give the sleeping brain the chance to say, “Look, this is the stage of sleep where you’re going to see the correlation with the benefit that you measure when you wake that individual up.” So we want to give REM and non-REM an equal opportunity to show their prowess in transacting a functional benefit for the brain. That’s why we usually do 90 minutes.

But if you’re trying to optimize napping, I should probably do a podcast on this myself, on the optimal version of napping, the short and long of it is, nap for about 15 to 20 minutes and no longer, because when you nap for longer, what happens is that you start to go down into the deeper stages of non-REM, and then when you wake up after 30 or 40 minutes, you’re coming out of the deeper stage of sleep and you have what’s called sleep inertia, which feels like a sleep hangover, and it’s even worse when you wake up than it was before you took the nap. But if you do 15 or 20 minutes, you don’t get that heavy hit of sleep inertia, but you still get sleep benefits. Once you get down to about nine, eight, or seven minutes, we really don’t see brain or body benefits. Getting to 15 to 20, you get some nice cognitive benefits, but you lose the downside of the sleep inertia affect.

But I’m digressing, so that’s sort of the sleep before learning, you also need sleep after learning, however, to then take those new memories and, as we mentioned before, to sort of fixate them into the neural architecture of the brain. It is like hitting the save button, but the problem is, it’s not digital in your Word document, which happens in milliseconds. The saving of memories in the brain is an organic process, it requires the building of new proteins between your synapses, so it takes hours. But it takes hours not just during wake, but during sleep. And there, what we found is that it’s during deep non-REM sleep or deep non-rapid eye movement sleep that the brain will cement those new memories. It’s almost like that scene in Jurassic Park where the amber has fixated the fly in perpetuity. And sleep futureproofs the information within your brain. And this perhaps comes onto both the mechanism, but also the idea of time that we discussed or that we should discuss, perhaps.

Tim Ferriss: Yeah, could I pause before we get to time just to ask about the kind of neuroanatomical or plausible mechanisms for ongoing need for sleep in order to have accurate recall later? Now, I may be misremembering this, but when I read your book, one of the studies that seemed to hop out to me, maybe I was having a fever dream, so please correct me, but it was looking at sleep deprivation at different points after initial acquisition of knowledge. So you had students who were studying, and this may have been alcohol-related, as well, so you’ll have to clarify for me, but one might think sleep before learning, important, yes, of course. Sleep, say, the night after learning, important, yes. But as I recall, it was something like three days later, if you interrupted the sleep, whether by deprivation or alcohol, that you subsequently saw lower recall scores, something like that. Am I inventing this?

Dr. Matthew Walker: Yeah, no, your memory is pinpoint accurate. So your sleep is not, perhaps, quite as bad as one would fear. You’re right. So we’ve done these studies and there are perhaps two studies that speak to your point. One of the studies, you have people learn some information, and then you deprive them of sleep the first night after learning. But then you don’t test them, you give them all of the recovery sleep that they want on a second night and a third night, and then you test them. And what we find is that the memory recollection is still impaired out on day five. So, in other words, if you don’t sleep within the first 24 hours after learning, you lose the chance to consolidate those memories. So sleep, for memory, is an all-or-nothing phenomenon. And if you’re not snoozing that first night, you’re losing, and no amount of recovery sleep, on the second or the third night, was going to salvage the process because it seems as though that there is a selective time window of opportunity for consolidation and if you miss it, unfortunately, it’s gone.

So in that way, sleep isn’t like the bank, that you can’t accumulate that debt and then try to pay it off at a later point in time. That was the first study. Then, there was another study done by Carlyle Smith, a great memory researcher, we didn’t do the study, but I’m so jealous, because it’s such a brilliant study. He was looking at different forms of sort of creative learning, which we know is more dependent on REM sleep. Learning facts, textbook information, and saving that stuff, that’s about deep non-REM sleep and we can speak about the mechanisms. When it comes to integrating and associating the information, as we spoke about, that’s more about REM sleep. So he did a very clever study, he knew that one of the major consequences of alcohol’s disruption on your sleep is not just that it sedates you, not just that it fragments your sleep, but it’s very potent at blocking your dream sleep, and the reason is because of the aldehydes, the metabolic byproduct, and something called acetaldehyde is the main reason that your REM sleep is demolished by way of alcohol.

And he was very interested in this idea, because we knew at the time that REM sleep, dreaming, was associated with this type of creative memory. So he took a group of individuals and he separated them into about four or five different groups and everyone learned this information on the first day, which required them to sort of create — it was actually very much like learning a novel language. It was an abstract analogical language, almost like learning a computer code that’s completely foreign to you and it’s not just about learning the individual pieces, it’s understanding the grammatical rules of this big picture structure, associative. So they learned it on day one, and then out on day seven, they tested those individuals. So they learned it without any alcohol in their system, and then they were tested seven days later without any alcohol in their system.

But here was the clever twist, one group across those subsequent six nights, they slept normally with no alcohol. The second group, the first night after learning that information, they got them, essentially, just to the point of inebriation, to about the point of being blood alcohol illegal, 0.08 percent, and it was a body standardized dose across individuals. So you had one group, the control group, the second group they got a little bit tipsy on night one, and then the subsequent nights they were alcohol free. Then there was a third group of individuals who had — they learned on day one, sober, then they had natural sleep the first night, no drinking. Then they had natural sleep the second night and no drinking. And then, on the third night, that’s when they dosed them with alcohol, and then, again, everyone was tested on day seven.

And what did they find? Firstly, relative to the group that got a full night of good sleep every single night across the six nights, their memory was still there, it was present. But in the group that had alcohol dosed on the first night, there was a greater than a 50 percent loss of their memory out on day seven, because of the impact of alcohol on night one on REM sleep. But the frightening part was the night three group. So the third group, they were very good, they said, “Okay,” let’s say it’s a student, “I’ve been learning on Wednesday and I’ve got all of this information, I’m not going to go out with my friends drinking on Wednesday night because sleep is important for memory, and then I’m not going to go out on Thursday night because I’ve just learned all this information, but then, on Friday, surely, my memories are now safe. I’m going to go out. I’m going to have a few drinks. Au contraire, because even alcohol on night three caused almost the same. It was about a 40 percent deficit in memory. And what that tells us is not just something about alcohol, it tells us that the sleeping brain is still processing and consolidating and digesting information three days after the act of learning itself. Yeah, it was a great study, and you’ve got a fantastic memory. Yeah.

Tim Ferriss: That’s the one that the blew me away, and I was like, “Oh, my God.”

Dr. Matthew Walker: It’s tough, isn’t it? It’s like, “Please, come on.”

Tim Ferriss: I know. Why does biology have to steal all the fun? But it raises all these interesting questions that, again, not to belabor the point, but having been very involved through the Saisei Foundation with funding various scientific initiatives, science costs money. And there is federal funding and you have NIH and so on, but some of these studies are probably unlikely to be done any time soon. But I wonder what the fragile plasticity range is for, say, associative/creative work versus straight declarative, memorize this list of 35 things, right, and if those windows are different. I would imagine they probably are, it’s hard to say, but it highlights for me, yes, we know a lot of things, but how many exciting questions there are that we don’t have, as of yet, really clear answers to.

Dr. Matthew Walker: I think that’s a really interesting point when it comes to therapy because therapy is not just about targeting any one individual memory, it’s trying to put it together both in the context of your back autobiography catalog of knowledge and experience and it’s also, often in therapy, trying to recontextualize it with new information to dissipate the negative affect. That is an incredibly complex thing for a memory system to achieve. In other words, what you’re trying to do is break previous associations, form new associations, and change, essentially, the emotional and the informational weighting of memories and the weighting of the different connections, dissipate some, increase others. That’s a process that I suspect does not happen across one night of sleep, it happens across multiple nights of sleep, and I think it has implications for therapy too.

Tim Ferriss: Have your therapy on Monday and not on Thursday if you’re going to drink on the weekends.

Dr. Matthew Walker: Exactly, before you go out, yeah. I think it’s very —

Tim Ferriss: I’m not kidding, right? It sounds like a flippant comment, but — 

Dr. Matthew Walker: No, I don’t think it is a flippant comment. Look, life is to be lived. Have a drink, of course, I’m not being puritanical, but if you are, let’s say, a student or you’ve been learning new information for a new job or you’ve been learning a new skill for a new particular sport and you know when you’ve been learning and you know when you probably want to have a night out, restructure those things to implement them in the smartest way possible for optimizing outcomes.

Tim Ferriss: Yeah. I will say, fortunately for me, in college, I have just a strange pseudo-allergic reaction to most beers, so given that I was dirt poor, along with most other students, that was the only thing really on offer, so I didn’t drink very much. I did pull a lot of all-nighters, and what I would say, and this is not to encourage anyone to pull all-nighters, but if there’s a 20 to 40 percent penalty, but you have not covered 80 percent of the material that might be on a test, you could still hypothetically net out positive, right, which is not to say you should do it.

Dr. Matthew Walker: Yeah. No, I think that’s very true, but one of the other interesting things that we did a study, and we never actually ended up publishing the data, we wanted to do some follow-up studies, but it comes on to this point. I think you’re right in that logic that, if you’ve not learned 80 to 90 percent, even though your learning is going to be 20 to 40 percent deficient in its capacity, time on task in that break-glass-in-case-of-emergency situation is still going to be in your favor, you could argue, setting aside, of course, all of the deleterious consequences that come of that night of sleep. Not to mention, if you’re driving to your exam the next day, your chances of getting in a fatal car accident are astronomically high.

Tim Ferriss: Oh, so bad.

Dr. Matthew Walker: But let’s just put that aside for now. Let’s think about it from an educational context, because I wrote an op-ed for when I was back as faculty at Harvard and I was asked to write a piece for the Harvard Crimson. We’d just published some work on sleep and memory, some of the first in that area, and I wrote the op-ed and said the frequency of pulling all-nighters at the end of the semester for exams is so rife and it is not the student’s fault. The fault is us, the faculty. Why? Because we end-load the semester with all of these inane, idiotic exams, and no wonder, what do you think is going to happen? You’re putting students in a pressure cooker, of course, they’re all going to be pulling all-nighters, and it’s counterfactual to the very idea of higher education.

It’s not the student’s fault. We are the people at fault and we need to reorganize and restructure how we examine individuals. Now, of course, that was the last time I was ever asked to write an op-ed for the Crimson. I suppose that told me everything I needed to know. But it comes on to my point, which is this: what’s the goal of education? The goal of education, in my mind, is twofold. The first is to brainwash you into thinking for yourself. The second is for you to gain long-term information.

We did a study where we suggested, okay, you haven’t learned any of the information, and we tested your hypothesis, and sure enough, yes, time on task returns some degree of a greater benefit if you pull the all-nighter. And they were better in terms of the testing relative to if you chose, obviously, not to engage in the material at all. At that point, there’s no learning whatsoever. Of course, you’re worse. What was interesting, however, is that, in the people who had the same amount of learning opportunity, but then got a full night of sleep afterwards, relative to the next day, yes, the people who got sleep were better than those people who were sleep-deprived, but then we brought them back four weeks later, and then we tested them a second time, and the difference between those two groups now was magnified almost tenfold.

In other words, the people who had been sleep-deprived the first night, yes, they could still test to a degree, they were worse, but they still got some degree of the answers right, but the amount of catastrophic forgetting that happened across those following four weeks relative to the group that imprinted those memories and saved them the first night was far less. There was a lot less forgetting in the group that had — and I put this in context simply because I don’t want to simply educate human minds, which is what I do as a job, only for you to test well the next day, but then, two years later, you’ve got none of that information in your brain. What’s the point of higher education then? It should be long term. And so it’s a very insightful suggestion that you make, and we tried to test it. I should publish some of that data.

Tim Ferriss: Question on that study, were the groups randomly assigned, or were the members of each cohort choosing which cohort they wanted to belong to?

Dr. Matthew Walker: No, they were randomly assigned.

Tim Ferriss: I was just wondering because I was thinking, if somebody chose to be in the sleep-deprivation group, their self-care might suck over the subsequent four weeks.

Dr. Matthew Walker: Yeah. Now I would say, though, the study is partly flawed in terms of its selection bias because, ahead of time, we tell them in the consent form, “Look, you could be in a group that is going to be sleep-deprived or a group that you’re going to have your sleep well-rested and full, and so would you like to continue?” In some ways, they know that they’re rolling the dice, they could or could not be sleep-deprived, and so you could argue there’s still a selection bias in that regard, but we don’t do selection assignment. We do random assignment.

Tim Ferriss: Science is hard, man. It’s like people, I shouldn’t say people, that’s too broad, but a lot of folks don’t realize just how hard it is, right?

Dr. Matthew Walker: It is, but — 

Tim Ferriss: It’s really hard.

Dr. Matthew Walker: — it’s so rewarding though.

Tim Ferriss: It is. It is.

Dr. Matthew Walker: At the moment when we analyze the data, and I’m sitting there with a student or I’m analyzing data, and we finally run the statistics, at that moment in time, if I’m lucky, I know something that has never been understood in the entirety of human civilization, and I cannot tell you how much of a thrill and a privilege that is. And so is science hard? It’s brutally hard, but just that alone, the hedonic rush that you get from de novo knowledge, gosh, it’s never left me, and I don’t think it ever will.

Tim Ferriss: Yeah. Yeah, what a drug.

Dr. Matthew Walker: It’s quite the drug. Get a belt around my arm, the vein is up, and I will go intravenous with that all day long.

Tim Ferriss: I want to ask you about sleep spindles because you mentioned that in the context of napping and how that seems to be a determining factor or a critical factor in later performance, cognitive performance. I want to come back to see if there are any levers you can pull, even if you wouldn’t recommend them for a long period of time, right? Are there levers you can pull to increase the frequency or amplitude of these sleep spindles? And I say that not really knowing sleep spindles well, but I’m planting that seed, so I’m going to let that germinate.

But, first, I want to tell you a personal experience and see how you might speak to it because I have a pretty good out-of-the-box memory, I think my hardware and genetics are reasonably good for it, but I’ve had a few outlier experiences that are still, to this day, stand-out experiences, and one of them was, while I was studying at a university in China, and we were responsible, at the advanced levels, for being able to produce, so not just recognize, but also actively write many thousands of characters, and some of these characters have 15, 20 strokes. They’re very intricate.

And I had this experience of getting very sick. I can’t remember exactly what caused it, maybe I never learned what caused it, but I had a fever. And there was this big exam the next day, and it was mostly characters, but in the context of essays. It was not just memorizing characters and being familiar with new terminology, some of it, very abstract. It’s not like the cat, it’s like hyperinflation, that kind of stuff. And I was bedridden because I had a fever, but I knew this test was coming the next day, and I had a very high fever.

And the way that my studying proceeded was I would wake up for 30 minutes and study super intensely, and then I would feel really sleepy and I would just fall asleep right on the book on the bed, and then I would wake up and I would do another 30-minute burst and then fall asleep. And, when I went into the test the next day, I was feeling somewhat better, but I’d slept a lot of the previous day, and I’d studied a lot of the previous day and it was intended to be, I want to say, maybe a 90-minute or two-hour exam. And I finished the exam in something like 25 minutes and I handed it in and they were like, “What are you doing?” and I was like, “I think I’m done,” and they’re like, “You can’t be done,” and I was done.

Not only was I done, but I scored 95-plus percent on the test, and that blew me away and I don’t really have a great way to explain it. And maybe it was just a freak incident and I’m reading too far into it, but I’ve spent a lot of time around very, very, very smart people, including people who have very impressive memories, and, for me personally, in my life, I think I’ve done a good job of learning many different skills and memorizing many different things, but that particular test stands out as very unusual. Do you have any thoughts on that?

Dr. Matthew Walker: Yeah, I do, and I think it comes back to the neural mechanisms of memory consolidation. There are at least two different mechanisms, non-mutually exclusive, that promote the cementing of that new information, but also the freeing up of your short-term memory capacity. And what we’ve discovered, we and others have done this work, the first method is a file transfer mechanism that, when you go into deep non-REM sleep, which, by the way, is dialed up by way of infection, when you get sick, you have an increase in sleep drive, particularly for deep non-REM sleep. We know why. There are a number of immune factors, inflammatory factors, that call up to play this thing called deep sleep. Those immune factors are things like cytokines and they are very sleep-inducing. That’s why you typically want to curl up and get into bed. That’s why you typically sleep more when you are sick because the human organism understands that the very best health insurance policy that it has, the very best Swiss Army knife of health, is this tool called sleep, and it brings all of the armament of sleep to the call.

Part of the reason you were sleeping so much is because you were undergoing the infection. You had a supercharged amount of deep sleep, it turns out. What happens, the first mechanism of deep sleep, is that during — and it’s not just the sleep spindles, and it’s not just the big, powerful, slow waves of deep non-REM sleep, it’s the combination of those two that we’ve discovered. We’ve published some work where, as long as you get this perfect timing between a slow wave and then a sleep spindle, it’s almost like making sure that the drummer is directly on the beat in this rhythmic capacity, so you have a slow wave and then you have a sleep spindle riding on top of it, this electrical burst of activity.

The slow waves, they go up and down maybe once or twice a second. The sleep spindles, they burst at about 14 or 15 times per second, 14 or 15 hertz. And it’s the timing, the combined quality of these two deep sleep brainwaves, that will shift memories from a short-term, vulnerable reservoir, the hippocampus, to a more permanent long-term storage site within the brain and protecting them. And that long-term storage site is the cortex that sits on top of your brain. I don’t want to do computer-brain analogies, but I suppose the idea would be your hippocampus is a little bit like a USB stick, that it’s very good at running around during the day and grabbing individual files from different locations, but it has a limited storage capacity. But then, at night, you shift those memories from that short-term reservoir of the hippocampus to the hard drive, the cortex, which gives you two benefits.

The first is that that which you learned before sleep is now shifted over and protected and safe in the new location, but the second benefit is that, because you’ve cleared out the USB stick of the hippocampus, when you wake up, you’ve got a refreshed learning ability and so you can start acquiring new files all over again. It’s a symbiotic relationship that we’ve discovered. And I think that’s one of the explanations for why you were able to just rip through the material, do it in a short burst. 

By the way, we know that that’s optimal for learning. It’s called massed versus spaced practice. If you try to learn in one long bout, not great. If you chunk it up into different segments, your learning is much better. You still spend the same two hours of learning, but, if you spread it across four hours than two hours straight, much better. But sleep is a part of that. That’s the first of the two mechanisms.

Tim Ferriss: That’s fascinating. I have a number of follow-up questions. The first is just on the — there are many different iterations of spaced repetition, but in these short-burst study sessions is, how do you explain the benefit of that versus longer duration? One thing that leaps to mind for me, which may or may not be true based on your read of the literature, but is that you have this primacy and recency effect in any given study session, but you can, in a sense, keep the — what that would mean is the first thing you study and the last thing you study, you’re generally going to recall, say in a word list, better than things in the middle. Okay. Now, if that’s true in a four-hour session, you have, let’s just say, this almost Golden Gate Bridge, high-tension wire type of dip in the middle, but, if you have shorter sessions, the actual drop of that high tension wire is going to be less, so your average retention over each individual session will be higher. And maybe that’s just me spouting nonsense, but that’s what jumps to mind. Does that mesh?

Dr. Matthew Walker: No, it does mesh very well, which is that you’re getting the primacy and the recency. It’s like this bow shape where the information in the middle of the list, you don’t remember very well, but the stuff at the front and the back end of it, you do remember well. Well, if you do only one learning session, you only get two stanchions, either end of the bridge of primacy and recency, but, if you split it up into six chunks, then you’re getting six hits of primacy and recency, which gives you a greater benefit. That’s one of them.

The other we think actually relates to attention, which is that your ability to focus and attend and have a spotlight of attentional focus, you need attention to imprint information, at least consciously, there is non-conscious learning too, and when you are constantly time on task, that spotlight of attention starts to fade and your ability to focus on what you should learn decreases and therefore what you learn decreases. It’s not really related to the fact of your memory fatiguing itself, but I think there’s evidence for that too.

One of the things that I’ve always been fascinated by, and I want to do the study, but it’s one of those bucket-list studies, I don’t think it’s quite as simple as that. I, at least, have found in my own personal experience, and heard from others, that I could be learning information about organic chemistry for an hour, and I just know that I’m just starting to fade. My learning is just getting miserable. It’s just diminishing returns at this point. But then, if I close the book and I start trying to learn French, I actually think my learning capacity is renewed and refreshed. And so I think there is something about the context of the information that the familiarity versus the novelty can also reinstantiate your learning ability. Does that make some sense?

Tim Ferriss: Yeah, yeah, totally makes sense.

Dr. Matthew Walker: I think this idea of fatigue, we don’t really understand it.

Tim Ferriss: No. Yeah. There seem to be these compartmentalized capabilities. It’s very — 

Dr. Matthew Walker: Isn’t that — 

Tim Ferriss: It’s wild. It’s so wild. I will say for folks, also, I use the example of word lists, but having attempted, somewhat successfully in most cases, to acquire different skills, motor skills, sports, et cetera, different capabilities, it could even be something like poker, which is a combination of all sorts of things, that the same type of short duration sessions and breaks help. It’s not limited to pure, what we might consider book learning, at least in my experience. Let me ask two questions and I’ll let you pick the first one. I’d love to hear you comment on both though.

The first is, if you wanted to put your sleep spindles on hyperdrive for a short period of time, who knows, final exam, right, I expect the slow wheels of institutionalized academia will probably not completely reformat the end-of-semester testing default that they have had for so long, so if someone had infinite resources and they wanted to put their sleep spindles on hyperdrive, how might they do that? The other one is you mentioned a term earlier with respect to lucid dreaming. That was charlatan science. It was considered charlatan science for a long time until it wasn’t. And I would be super curious to know if there’s anything that is currently, and this might make you uncomfortable, but I’ll do it if there’s anything that is currently considered along the lines of charlatan science that you think might similarly bear out as lucid dreaming did?

Dr. Matthew Walker: In terms of the sleep spindles, and I wouldn’t probably just focus on the sleep spindles, I would focus on the combination of deep slope brainwaves and —

Tim Ferriss: The synchronization.

Dr. Matthew Walker: — yeah, the synchronization of this. What we call it is phase amplitude coupling is the technical term, which is — 

Tim Ferriss: Yeah, that makes sense.

Dr. Matthew Walker: — the phase of the wave and the coupling of the peak of that.

Tim Ferriss: Two people jumping on a trampoline at the same time.

Dr. Matthew Walker: Exactly, yeah, and you want those to just go just in this lovely rhythmic sync. We’ve been developing some brain stimulation technology to see if we can do this. We can certainly boost your deep sleep brainwaves with brain stimulation. We can also improve your sleep spindles. And, here, what we’re doing is we’re applying electricity through the brain where you don’t feel it it’s so small, it’s a small voltage, but we can stimulate the slow frequency brainwave and we can act like a choir to that flagging lead vocalist and boost those slow waves, but we can also stimulate at the frequency of the sleep spindles, which is a much faster frequency, somewhere between 12 to 15 hertz, 12 to 15 cycles per second, and we can also induce those sleep spindles.

By the way, motor learning is another good example. We did some studies, gosh, 10 years ago now at least where we found that motor skill learning was also dependent on lighter stages of non-REM sleep, but, once again, on sleep spindles. And a recent group, this wasn’t us, although we’re doing these studies too, they applied stimulation at the sleep spindle frequency range and they were able to improve aspects of motor skill learning as well, which is wild when you think about airline pilots, musicians, and professional athletes. Can you actually adopt and learn some of these new skills and then supercharge them overnight with electrical brain stimulation? Is that going to be, in 10 years time, a banned electro-ceutical rather than a banned pharmaceutical in sports?

Tim Ferriss: Yeah, or will it be a required electro-ceutical for, say, airline pilots and what ethical questions does that raise, right?

Dr. Matthew Walker: Exactly, and what are we trying to do, and always got to think about free lunches and if you ever get one. I would say that that’s probably one of the areas. I would also say that the sleeping brain often takes care of itself. What we’ve learned is that, when you have people do intensive learning sessions and you measure their sleep that following night relative to when they’ve not been doing intensive learning sessions, lo and behold, the brain after the intensive learning session, artificially for that night — it’s not artificially. Adaptively for that night, increases the amount of spindles that it gets. Your brain actually knows what it needs and it self-medicates with greater numbers of spindles.

Tim Ferriss: How cool.

Dr. Matthew Walker: So we may almost not need to worry about that. Yeah, it’s wild, isn’t it? When we made that discovery.

Tim Ferriss: What an amazing piece of wetware we carry between our ears. What a thing.

Dr. Matthew Walker: Yeah. The other aspect of memory that you could optimize, and people have been doing this, and I don’t think it’s mainstream yet, comes back to the second mechanism of why sleep is good for memory. It’s not just about shifting memories from short term to long term. It’s about memory replay. And this study, or this story, emerged back in the 1990s when a scientist called Bruce McNaughton at the University of Arizona, he was measuring the memory cell activity in rats as they were running around a maze and he was trying to learn how the hippocampus codes a maze and, basically, how it builds a memory circuit of the maze. And he was recording individual cells in the hippocampus, and he wasn’t doing this, but you can just think of this as each cell has a tone to it and, as the rat would run around the maze, what he would hear is the signature of learning that would sound a little bit like (singing).

As the rat was running around the maze, he was listening to the brain imprinting these memories. The brilliant part of his study was that he didn’t stop recording when the session ended. He kept recording from that memory center as those rats went into sleep and went into deep non-REM sleep. And, when they went into deep non REM sleep, he kept listening. And, when you eavesdrop on the sleeping brain, not only was the memory replayed, but it wasn’t replayed at waking speed. It was replayed almost 10 times faster. Instead, what he was hearing, instead of (singing), he was hearing — as if these rats were just replaying the memory at high frequency speed as if they’re etching the memory into the glass surface of the brain and scoring the memory trace even more powerfully. We know that memory replay is a critical component of that.

Then studies — it probably restarted back with some French scientists in the early 2000s, and then there was a big paper in Nature by a German group, and they tried to hijack the system of memory replay, and it was brilliant. It was so clever. And now Ken Paller at Northwestern has been doing some of these studies. Here’s what they did. They had people learn information, but they associated that information with somatosensory stimuli. And what I mean by that is you’re learning a list of words and then, during that list of words, I am infusing a rose perfume up your nose with a mask, and what you’re doing, the brain is bonding the scent, the odor, of the rose with the learned information, so now you’ve got a bonded memory with the odor.

Then what they would do is they would let those individuals fall asleep and, during deep non-REM sleep, when we believe the memories are being replayed, they started to reperfuse that rose odor up their nose. And, as a consequence, the next day, there was about a 40 to 50 percent improvement in their memory because they had brute-forced the reactivation of the memory. It’s almost as though they decided to take that memory and give it VIP access to the memory replay during non-REM sleep, and you start to cherry-pick information. And then Ken Paller and others, they started to look at this and they did it even more cleverly.

I think the way the game over here in America is actually called Memory, where it’s a set of cards all out on the table, and each card has its own pair. You turn one card over and it’s a house and you turn another card over, and somewhere in the rest of the deck there is another house that’s the match. And then there is one teakettle and then there is one fire engine. And so they would do all of these things. But they did this on the computer, and each time they were learning this associative spatial layout of information. When they would turn over the teakettle, they would hear a teakettle sound, and, when they’d turn over the fire engine, they would hear a fire engine sound. Once again, they were bonding a sound, a congruent semantic sound, with that particular information visually. And then they let them sleep.

And, as they went into deep non-REM sleep, they would replay those sounds at what we call a sub-awakening threshold, where it was loud enough to get into the brain, but not loud — 

Tim Ferriss: Critical detail for people asleep.

Dr. Matthew Walker: Yeah, please, please, please don’t do that. And what they were able to do is, essentially, an even more selective process of cherry-picking. Now, whatever I want to serve up to the menu of this thing called sleep at night in terms of the different dishes of memory, I get to choose. I can say, “No, no, no, I don’t want that information. I want this particular information tonight and I’m going to develop this auditory playlist.” And so the question then becomes can you start using that method? Is the cheap version of that that I’m going to study organic chemistry and I’m going to blaze up some green tea incense, which I personally really like, and then, before I go to bed at night, am I going to put back on the green tea incense and start trying to stuff that back up my nose and either improve my memory or burn my house down and be a scientist no more and chargrill the rest of my body, because it’s a desperate fire safety hazard and you’d never want to do it?

But this is the idea, that there’s something that we’re starting to understand about the sleeping brain that not just is understanding, but it gives us the ability to take control. And, at that point, that becomes scary because should we be taking control of a process that maybe is not really our purview to be in control of?

Tim Ferriss: Sounds like the story of humankind in a nutshell right there.

Dr. Matthew Walker: Yeah, I know. Yeah, you can almost see visions of the atomic bomb. By the way, I would say that, it’s a bit extreme, Matthew, but what happens during REM sleep is really quite different. It’s during deep non-REM sleep that those memories are replayed at, as I said, about 10 times faster. But, when you go into dream sleep, and this is work done by Matt Wilson, not me, Matt Walker, Matt Wilson at MIT. He found that the rat brain does replay memories during REM sleep, but it doesn’t replay them faster and it doesn’t even replay them at waking speed. It replays them at about 0.5 times the speed. It’s like listening to this podcast and, all of a sudden, you hit that button that says — 

Tim Ferriss: Yeah, 0.5x.

Dr. Matthew Walker: — go slow and everyone slows down. And I think this has relationships to the component of time and our time perception, which is totally freaky, by the way. Time, and I’ve written about this and have a few theories and we’re really interested about how to do this — by the way, I haven’t forgotten about your question, as to what is charlatan science, and I will come back to that, because I’ve vaguely still holding onto my memory despite being in the foothills of middle age. The time perception is interesting. When you and I, let’s say we go on a long-haul flight, and you’re lucky enough to actually fall asleep on the flight, and it’s dark on the flight. When you wake up, what is one of the first things that you do? One of the first things that you do, is you check your watch, you check your phone, because you’re trying to look to the time. Because when you sleep, you lose all conscious perception of time. You’ve got no idea. And that’s the reason that you check, “How long have I been asleep?”

Well, why don’t you know? I don’t know, because I don’t track sleep time when I’m sleeping. However, when you dream, something different happens. And maybe you’ve had this experience. I certainly have, and many people have. Your alarm goes off, and you have a snooze button, and the snooze button is for five minutes. So the alarm wakes you up, and you hit the snooze button. And you were dreaming, and you go back to sleep and you go back to dreaming. Maybe it’s the same dream, maybe it’s a different dream. And then the alarm goes off again, and it’s been five minutes in the waking world. But you, personally, you think, “That wasn’t five minutes. I felt like I was dreaming for 20 minutes, 30 minutes, 40 minutes.” As if time is different in the dreamscape. And what I’ve described this as is time dilation. That it’s during dream sleep, that we almost stretch time out.

What would be the neurobiological basis of that? Well, I think it could be some of this rat work that suggests that perhaps during dream sleep, the brain slows down the recapitulation of time. And you can have all sorts of fun with this idea. Christopher Nolan was wise enough to consult some sleep researchers, and come up with this idea in Inception, where we’d have different dream levels, where in the first level, five minutes in the waking world is now 50 minutes at the first level of the dream. And you go down the next level, and now five minutes is now five hours, and then the next level it’s five years, and the next level it’s 50 years. And you’re constantly doing this sort of time dilation, as it were. It comes up with some fascinating ideas, but science is just getting to that position now, where we can understand time during sleep. Because it is strange. It’s a very strange thing, time, with sleep.

Tim Ferriss: Yeah. I mean, if you sit with that for a minute, I mean that is one of the strangest experiences that is very hard to fit into our sort of paradigms of thinking about things right now, right? I mean, the idea that you could have more than five minutes, you could have 40 minutes of experience, subjective experience, in five minutes of waking, Earth time. No matter if we take the fidelity of the firsthand experience to be high, in so much as it being a real experience, it raises a lot of very, very hard-to-answer questions.

Dr. Matthew Walker: Yeah, it’s fascinating too. And right now, I do have a neural hypothesis for this, and there’s a part of the brain called the insular cortex, that sort of is in the left and the right side, but it’s buried deep inside. And it serves many different functions, but one of its functions is the mapping of your bodily state, of your emotions, and the updating it, from one moment to the next, to the next. So the insular cortex is consistently mapping the physiological state of your body, from one moment, to the next, to the next. The reason I bring that up is because the physiological emotional state of your body contributes to time. How does it do that?

I think you and I, and everyone listening, has also had that experience, where they said, “I just had this emotional experience, and all of a sudden time slowed down.” I remember when I was an avid cyclist, and I’ve been knocked off my bike a few times. And I remember one time, I was going through, and a car came out of a junction, and I could just see it. And it hit me, and I went through the windscreen of the car and came out. And that moment of time, which was, obviously, a pretty traumatic, pretty emotional event, when you get knocked off your bike through a car windscreen. Time just slowed down. The emotion was so intense, that all of a sudden it was like when you see on a video camera, you go from a standard frame rate, and all of a sudden — and you can now do it on your iPhone, you can slow it down, and you can get really high resolution, slow temp, or slow motion activity.

It was like that, because the insular cortex was starting to map with much higher frame rates, and therefore time slowed down. I realized I was going to be hit, and I realized I’m clipped into my pedals on the bike. I’m going to clip out, because I don’t want to go under the car, where my bike is going. I’d much prefer to go over the car, onto the windscreen, and off. So I remembered — 

Tim Ferriss: Wow.

Dr. Matthew Walker: And that happened, obviously, within milliseconds, but I remember clipping out, thinking all of this within time.

Tim Ferriss: Wow. Yeah.

Dr. Matthew Walker: And I think what’s happening is that the insular cortex has some interesting changes. We see it changing in its activity during dream sleep. My prediction is that if I start to map your perception of time in dream sleep, I think it’s going to be predicted by changes in activity within this part of the brain, called the insular cortex, which is constantly mapping the affective visceral state of your experience consciously. So I’ve got a neural theory. It’s hand waving, though.

Tim Ferriss: Yeah, the time machine.

Dr. Matthew Walker: Time machine. 

Tim Ferriss: So if I try to then just restate that, so I ensure that I’m understanding it correctly. Is it your insular cortex? No.

Dr. Matthew Walker: Yes. Insular cortex. Yeah.

Tim Ferriss: Insular cortex has the ability to effectively increase your frame rate in certain circumstances, which is ostensibly resource-intensive, and there’s a cognitive load, therefore it doesn’t do it all the time. Right? Because I mean, perception of reality, in a sense, is a shorthand, a lot of the times, of sorts. I mean, it seems that way at least, otherwise we would just be on psychedelics all the time, experientially, and that would be just unmanageable. I suppose where I wanted to — that’s just a restatement. Is that a fair lay restatement of what you just said?

Dr. Matthew Walker: It’s an accurate statement in the sense that the insular cortex does do that mapping of time, but it doesn’t seem to do it all of the time, and some of it probably non-consciously. But they have done studies, where let’s say that you ask people to, say, count time, count two minutes of time. And they’ll just sit there, and they’ll just try and sense time, quantify time. The accuracy from one individual to the next, in terms of mapping that subjective sense of two minutes, is predicted by the insular activity itself. The greater the insular activity, the greater your precision of mapped timing. So it really does seem to be one of the seats of mapped time.

Tim Ferriss: Yeah. It makes me wonder if this is one of the unmeasured performance-enhancing variables in, for instance, batters in major league baseball, who claim to be able to see the stitching on the baseball as it travels towards them as a fastball. How much of that is innate versus trained? If it’s innate, it would be very interesting if that were a deciding factor in performance in certain sports.

Dr. Matthew Walker: Yeah.

Tim Ferriss: Let’s hop to the charlatan science. No, hold on one second. So the question is not so much what is charlatan science, because I think that’s somewhat evident in the term itself. I think most people kind of grok what that means. The question is: what is currently being dismissed, or cast aside, much as lucid dreaming was for a long time, that may in fact become a credible area of inquiry in the foreseeable future? 

Dr. Matthew Walker: To me, and this is probably just because we’ve been talking about dreaming for so long, I do have a theory of dreaming that is currently not very well supported. Most science right now suggests, just as I did when it comes to dreaming, that we are amnesic, that we forget most, if not all, of our dreaming life, that it’s just not imprinted into our brains. I think that there could be a day and a time in the future where we realize we have been desperately wrong about this, and that our dreaming lives are influencing our waking lives in a far more powerful way than we ever thought. I was going to say dreamed, than we ever thought possible. And here’s the reason. We know that there is such a thing as non-conscious memory, or implicit memory, and I think people have conflated an issue with memory that is about accessibility versus availability.

And what I mean by that is you can learn some information, and it can be available, it can be there in your brain, that memory is present, but you, for whatever reason, lose the IP address to the memory, so it is not accessible. And right now, we have conflated accessibility of dreams, with availability of dreams, such that we say, “Well, you can’t remember most of your dreams, so we assume that that memory is not available, that that memory is not present in your brain.” I don’t believe that’s true. I think that memory could be present, available, but it’s simply not accessible. And the evidence I have for this, and it’s happened to me multiple times, I’ll wake up in the morning and I know for a fact I was dreaming. And the harder I try, I just can’t remember it, and it just seems to evaporate, as if the memory is gone. And the availability of the memory, its presence in my brain, we all assume in science, is no longer there. That memory has evaporated.

But then, two or three days later, I could be in the shower washing my hair. I look at the shampoo bottle, and there’s something about the label that triggers the instant recollection of that dream from three days ago, and it all comes flooding back. In other words, it wasn’t a problem of availability of the dream, it was a problem of accessibility of the dream memory. The memory is there, it’s just that I don’t have conscious access to it. Now, if that is true, and if I can prove that, and I’ve got some ideas. I mean I’ve always got way too many experiments than I can do, but if I can prove that that’s true, what that could unleash is the maybe scary fact that most of our dreams, firstly, are residing within us, and vast amounts of our dreaming life are non-consciously implicitly unaware to us, influencing our everyday choices and our behaviors. That, right now, sounds a lot like charlatan science. That sounds like hooey to me, that sounds like total BS.

Tim Ferriss: Oh, and strong words. Strong words, Matt Walker.

Dr. Matthew Walker: Matt Walker used to do some fairly hard-nosed, good neuroscience data, and then towards the end of his career, he kind of lost it. He was going on podcasts, and he started dreaming of all these crazy theories, and that was the end of him. Next we know, he is selling books door-to-door in some odd country. But I think that, to me, that could be a wild and plausible, currently charlatan nonsensical idea. But if we can prove it, and I think it’s a testable hypothesis, that’s why I entertain it, because I’m a scientist and it has to be a testable hypothesis. What does that mean for us as a species, in terms of what dreams do and influence, to us as a species, and us as a society?

Tim Ferriss: Yeah, and it’s also, if you can’t get the funding for the study, you might be able to sell it to Hollywood. I’m just imagining a film premise, where you have something like Waking Matt and Dreaming Matt. And those are certainly one and the same in some respects, but perhaps in the same way that you can consciously attempt to recall experiences, data, things you’ve memorized, from your waking life, perhaps through lucidity, you can query your dream memory, and be more active as a participant in that mindscape.

Dr. Matthew Walker: And sculpting that experiential —

Tim Ferriss: I mean, how amazing would it be if, and I’m getting way out there now, but if in the same way that you could try to recall, perhaps with the help of someone like a family member, what your fifth birthday was like, or what happened when you graduated from elementary school, and perhaps you could have a similar attempt, perhaps successful, at sort of aided inquiry to identify what your dreams were like when you were three, four, five, eight, 11. It opens up all sorts of narrative possibilities, if not scientific.

Dr. Matthew Walker: Let’s write the screenplay. I’m represented by WME. I don’t know if you’re with the same agency, but we should definitely — let’s do the joint screenplay, and let’s sell it for probably about $20.

Tim Ferriss: Yeah. It’s like, “Here’s a great idea, and it’ll cost just a mere $20 to $100,000,000 to try to do a test reel. Good luck.

Dr. Matthew Walker: Yeah, I’ll email Christopher Nolan, see what he wants to do.

Tim Ferriss: Well, yeah. If you can email Christopher Nolan, I’d love to have him on the podcast too, but that’s a whole separate conversation. 

So if we’re looking at a few different things here, I mean we’ve covered a lot of ground. I would like to chat for a second about my fever-induced hypermnesia, my experience with that Chinese test. And I was listening to you describe the cytokines, and inflammatory markers, and so on, which would be associated with that fever. And it raised the question for me of how you might simulate that without going out and eating rotten beef, or whatever gave me food poisoning, because I wouldn’t recommend that.

And then I started to think about exercise, and its relationship to, or how it might affect, sleep and memory. And certainly, you have a whole cascade of things that can happen with different types of exercise, including brain drive, neurotrophic factor, into all these various things. But I was wondering, if you go through intense exercise, let’s just say intense resistance exercise, you are going to trigger, I would think, many of the same type of inflammatory responses and compensatory mechanisms that you might when you are experiencing an infection, in a sense. And they’re not identical, I’m not saying that, but where I’m going is, I’m wondering if there’s a role for intense exercise, that is pro-inflammatory in the short-term, for enhancing memory.

Dr. Matthew Walker: I think there is, and it’s funny you should mention that. Literally this week, on my podcast, I released the first of a three-part series, all about sleep and exercise. And it’s exactly what you predict, that exercise is hugely beneficial for sleep. The principle stage of sleep that it seems to induce is an increase in the amount of deep non-REM sleep, and particularly the power of those powerful, big, slow brainwaves. One of the interesting things is, though, that there is no free lunch, that when you exercise intensively, if you look across the studies, yes, you increase the amount of deep sleep, but it does seem to come at the cost of REM sleep. That you will have a reliable and statistical drop in the amount of REM sleep. Now, I don’t think that’s anything to be concerned about if you are exercising. I think it’s simply that, once again, mother nature knows what the menu of sleep stage options should be, and prescribes the right one for whatever conditions you’ve been doing that day. Whether it’s physical exercise, whether it’s learning intensively material, that is figured out for you.

But you are absolutely right; exercise will induce that. Part of that is because of the low-grade inflammation, that it’s a pro-inflammatory state by way of exercise. I think there are other factors too, that probably help with that. Some of them may be related to temperature, some of them may be related to the degree of parasympathetic down shoot that you get after exercise. So you get very sympathetic and stressed, in terms of the nervous system, of course. But then you typically have this drop that comes down, and you dip below your typical level. That’s what you see in heart rate. You see it in blood pressure. That’s one of the benefits of exercise.

So I think this nice down shoot, shifting from the fight or flight, down to the parasympathetic, in part, is one of the reasons why you get better sleep by way of exercise. It benefits across all ages, by the way. It’s not just that young people benefit from exercise, all people do as well. You can look at different forms of exercise. And right now, I don’t think there’s enough data. There’s some data that aerobic versus resistance training may lead to somewhat greater benefits on sleep, at least on deep non-REM sleep, and the consistency — 

Tim Ferriss: You’re saying on the aerobic side?

Dr. Matthew Walker: So aerobic seems to, potentially, outdo if you put them head-to-head in a sort of Coke-Pepsi challenge. It seems to be that aerobic wins out, somewhat, relative to the, sorry. So yeah, so the aerobic, so basically doing cardio seems to produce a greater benefit relative to resistance training. In other words, lifting weights. But lifting weights is still better than doing nothing at all. So don’t feel worried about the fact that, “Oh, my goodness, I’m principally someone who just goes into the gym and lifts weights. I’m not going to get the sleep benefit you will, relative to being sedentary.”

That’s definitely the worst situation. But aerobic seems to, and of course it’s not, we call it aerobic exercise, but most of the time it’s anaerobic. It’s where you go without oxygen. That’s where all of the good stuff can happen to, although kind of Zone 2 as well, Peter.

Tim Ferriss: Well, hold on a second. So let’s talk about that for a second. So if we’re talking about anaerobic, does that mean that you’re talking about cardio, in quotation marks, that is above your lactate threshold, or otherwise sort of pushing the boundaries of your aerobic capacity, as opposed to lower intensity, steady state aerobics? Because the devil’s in the details with this stuff, right?

Dr. Matthew Walker: Yeah.

Tim Ferriss: And that’s true for resistance training, because there’s such a spectrum of different types of resistance training. And I’ll just say as a quick side note for folks, do both.

Dr. Matthew Walker: Absolutely.

Tim Ferriss: You really don’t want to have sarcopenia, and lose muscle mass year-on-year, as you get older. That is just a recipe for disaster. So do your weight training or resistance training. But when you say anaerobic in this case, what type of protocol are we talking about?

Dr. Matthew Walker: Yeah, so people have looked at HIIT routines, H-I-I-T.

Tim Ferriss: High-Intensity Interval Training.

Dr. Matthew Walker: Interval training, and they’ve also looked at steady-state cardio. Right now, I don’t think we have enough data to separate between those two. Simply that both of those will provide a nice sleep benefit, and a boost both in the — it’s not just that it boosts the amount of deep sleep, it also boosts the continuity of your sleep, meaning that you’re going to wake up fewer times throughout the night, and you’ll have a nice longer consolidated bout of total sleep as a consequence. That’s one of the other benefits of exercise on sleep. But again, resistance training also provides those benefits, too. They’re just not quite as voluminous.

Tim Ferriss: Mm-hmm.

Dr. Matthew Walker: But to your question, no one has done the systematic study, where you try to — I mean, it’s only now being worked out in the field of exercise itself, which is really understanding when you put all of these different flavors of HIIT, versus Zone 2. Exactly, what are the nuanced neurobiological and biophysical changes within the body and the brain regarding sleep? We’ve got no idea.

There are studies that have done these different flavors, but they’ve never done a randomized controlled trial, where you assign people to each one of these two in the same protocol, and then ask basically, Coke, Pepsi, Dr. Pepper, Sprite — whatever you want to line up, challenge, and put them all head-to-head, to see which one wins out. We don’t know right now.

Tim Ferriss: Yeah, it’s really hard, from what I can tell, to implement studies in exercise science, in a really clean, precise way. And I don’t want to name names, but I’ve, at many points, volunteered to be a subject in experiments all over the place, and in some very fancy places. I remember being in one study, and it entailed circuit training. And so you’d go to different stations, and you had to do bench press, pull-up, et cetera. There were a number of other subjects in this room, and we’re rotating around these stations.

And I would see one person doing bench press, very controlled, in a slower cadence, like four seconds down, two seconds up, and then the next two people would be bouncing the bar off their chest using momentum. And I just thought to myself, “The time under tension, and the loading here, is apples and oranges.” You’re not actually getting a clean signal, because it’s not standardized well enough. So that’s certainly a challenge, I think, with a lot of these studies.

Let me ask you, though, I’m going to do a hard left turn, just because you’ve inspired me, and I actually want to try to get to the gym now. But let’s talk about urination. So I love drinking beverages. I’m very well hydrated, and there’s a lot of upside to that. But one of the downsides is I almost always get up and pee in the middle of the night. That is not a new thing. I mean, I’m sure that the plumbing starts to wane in its strength over time, unfortunately.

Dr. Matthew Walker: It does, yeah.

Tim Ferriss: But this has been pretty consistent for me. I drink a lot of liquids. So the question is, and I’ll say a few more things, but the question is what are some approaches for minimizing this as an issue, as a problem? Because it does interrupt that continuity of sleep. And I see a market difference in my feelings of restfulness, on subsequent mornings when I do or do not get up to go to the bathroom.

Dr. Matthew Walker: Yeah.

Tim Ferriss: So one is drink less. Okay, fine. I seem to be very bad at following that advice. Another is, hey, take something like a desmopressin, which is an anti-diuretic hormone, that which no one should do without medical supervision.

Dr. Matthew Walker: No.

Tim Ferriss: I tested that. The problem is, I ended up experiencing orthostatic hypertension, where I would stand up and get really dizzy.

Dr. Matthew Walker: Dizzy, and then, yeah, potentially pass out. Yeah.

Tim Ferriss: I’d get really dizzy. And I thought, “Wow, that’s dangerous. I don’t want to screw around with it.” Are there any other techniques, or thoughts that you have, on this particular issue? Because I know a lot of men, in particular, seem to contend with it as they get older.

Dr. Matthew Walker: Yeah, I’ve definitely experienced this as I’m getting older. I used to sleep throughout the night. Now I probably get up, on average, at least once every second night, to go to the restroom. We don’t have a particularly good approach to this, in terms of medications. There are a few medications out there, to try to decrease the likelihood and the frequency of those. And I think those medications are more about trying to increase the expulsion of urine, such that before bed, you expel more of that fluid, and so less is left as you are casting off into sleep to trigger the awakening. But there’s nothing that I know that helps suppress that reflex and that desire during sleep. And it’s really, then, at that point, unfortunately, down to, “How do I taper off my fluid intake throughout the late afternoon, in the early evening, and is it worth it to me to get that continuity of sleep?”

Is it that I don’t stop drinking the number of drinks that I have, but starting at 5:00 p.m. or 4:00 p.m., I actually will just have half the size of the drink that I normally would. So I don’t fool my brain into thinking, “You are in a famine of fluid.” I still have the same number of drinks, so my habit is still satisfied with having three, or four, whatever drinks I’m having, but the volume is halved and therefore the psychology is still easier to adopt, but the impact is reduced by 50 percent. That’s one of the ways that you could try to, or at least I’ve tried to, get around the effect. And when people speak to me, I advise them that that’s what one method that you can try to fool your brain. Don’t feel as though you are stopping yourself from doing what you normally like to do, but you still get half of the fluid intake. Other than that, it’s very challenging.

Tim Ferriss: Yeah. All right. Well, I’ll try the Dr. Walker half-glass trick tonight, and see how that goes. I’ll report back. Matt, this has been so much fun. We’ve covered a lot of ground. Is there anything that you would like to mention? Anything you’d like to point people to? Certainly, I think we could refresh where people can find you online, just so they can track you down and see what you’re up to. So please feel free to add your closing comments.

Dr. Matthew Walker: Yeah, people can find me. I’m on Twitter, @sleepdiplomat. I’m on Instagram, @drmattwalker, that’s D-R-M-A-T-T-W-A-L-K-E-R. And I also have a podcast. If you’re not sick and tired of my voice. And it’s creatively called The Matt Walker Podcast, which can be found on all platforms. And that’s probably about it.

Tim Ferriss: All right. Well, thank you for taking the time, and I always enjoy our conversation — 

Dr. Matthew Walker: Just being a repeat offender, second repeat offender on the podcast, for all of the sins that I’ve offered, in terms of sleep advice. So thank you for having me.

Tim Ferriss: Oh, I’m all about repeat offenders.

Dr. Matthew Walker: Right.

Tim Ferriss: And of course, thank you for putting on the gloves. To everybody listening, we will have links to everything that we discussed in the show notes, as per usual, at And until next time, try those half glasses of water out, and see how that works. Let me know if — 

Dr. Matthew Walker: A little bit of sex in between, as well, and maybe — 

Tim Ferriss: A little bit of sex.

Dr. Matthew Walker: Yeah.

Tim Ferriss: Yeah, a little bit of sex sprinkled here and there. And if you don’t have a fantastic partner, then maybe your right or left hand will do the trick for that 47 percent.

Dr. Matthew Walker: Half glass full in left hand, keep your right hand free, and you’re good to go for sleep.

Tim Ferriss: Yeah. Be safe out there, folks. And as mentioned, till next time. Thanks for tuning in.

The Tim Ferriss Show is one of the most popular podcasts in the world with more than 900 million downloads. It has been selected for "Best of Apple Podcasts" three times, it is often the #1 interview podcast across all of Apple Podcasts, and it's been ranked #1 out of 400,000+ podcasts on many occasions. To listen to any of the past episodes for free, check out this page.

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One Reply to “The Tim Ferriss Show Transcripts: Dr. Matthew Walker, All Things Sleep Continued — The Hidden Dangers of Melatonin, Tools for Insomnia, Enhancing Learning and Sleep Spindles, The Upsides of Sleep Divorce, How Sleep Impacts Sex (and Vice Versa), Adventures in Lucid Dreaming, The One Clock to Rule Them All, The IP Addresses of Your Memories, and More (#654)”

  1. Hello Tim – regarding “I almost always get up and pee in the middle of the night” – I used to have exactly the same problem. There is a very effective solution for that which has worked 100% for me for years now. It is based on the circadian rhythm of urine production by the kidneys. It is very simple, as follows:
    Every time you pee in the night, it is “programming” your circadian clock of your kidneys to say that producing urine in the night is fine because it will be able to be expelled (by peeing). Therefore all you need to do is not gut up and pee in the night even if you feel that you need to. This is uncomfortable at first, but after a few days your kidney’s circadian clock will start to adjust and this need will diminish each day until it stops. Generally this is pretty much there within 1 week. To start with, to make it easier to “hold it in” and not get up, you may want to limit how much you drink in the 2 hours going to bed.
    If I travel to another time zone that is significantly different (e.g. Japan) then my kidneys will be producing significant urine at night again, so I have to do the same thing again, and also when I come back home again.
    So I now never have to get up in the night to pee – for me it is a 100% successful solution to this problem. I hope you fine it useful!