EVERY SPOKEN WORD
150 min read · 30,036 words- 0:00 – 2:05
Introduction
- LFLex Fridman
The following is a conversation with Matt Walker, sleep scientist, professor of neuroscience and psychology at Berkeley, author of Why We Sleep, and the host of a new podcast called The Matt Walker Podcast. It's ten-minute episodes a couple of times a month, covering sleep and other health and science topics. I love it and recommend it highly. It's up there with the greats, like the Huberman Lab Podcast with Andrew Huberman, and I think, uh, David Sinclair is putting out a, an audio series soon too. I can't wait to listen to it. I'm really excited by the future of science in the podcasting world. To support this podcast, please check out our sponsors, Stamps.com, Squarespace, Athletic Greens, BetterHelp, and Onnit. Their links are in the description. As a side note, let me say that, to me, a healthy life is one in which you fall in love with the world around you, with ideas, with people, with small goals and big goals, no matter how difficult, with dreams you hold onto and chase for years. Life should be lived fully. That, to me, is the priority. That, to me, is a healthy life. Second to that is the understanding and the utilization of the best available science on diet, exercise, supplements, sleep, and other lifestyle choices. To me, science in the realm of health is a guide for what we should try, not the absolute truth of how to live life. The goal is to learn to listen to your body and figure out what works best for you. All that said, a good night's sleep can be a great tool in making life awesome and productive, and Matt is a great advocate of the how and the why of sleep. We agree on some things and disagree on others, but he's a great human being, a great scientist, and as of recently, a friend with whom I enjoy having these wide-ranging conversations. This is the Lex Fridman Podcast, and here is my conversation with Matt Walker.
- 2:05 – 2:26
Putin moment: Lex takes Matt's sunglasses
- LFLex Fridman
You should try these shades on and see what you look like.
- MWMatt Walker
So they are now your shades?
- LFLex Fridman
(laughs)
- MWMatt Walker
And that's not a question.
- LFLex Fridman
It's the same thing as, uh, Putin took the Super Bowl ring and it's now his ring.
- MWMatt Walker
(laughs)
- LFLex Fridman
(laughs)
- MWMatt Walker
Uh, yeah, one wonders if he was offered it, but, um, they are yours.
- LFLex Fridman
(laughs)
- 2:26 – 6:35
Fascination with sleep
- LFLex Fridman
When did you first fall in love with the dream of understanding sleep? Like-
- MWMatt Walker
Mm-hmm.
- LFLex Fridman
... where did the fascination with sleep begin?
- MWMatt Walker
So back in the United Kingdom, you can sort of start doing medicine at age 18, and it's a five-year program, and I was at, uh, the Queen's Medical Center in the UK, and I remember just being fascinated by states of consciousness, and particularly anesthesia. I was thinking, "Isn't that inc- Within seconds, I can take a perfectly conscious human being, and I can remove all existence of the mentality and their awareness within seconds," and that stunned me. So I started to get really interested in conscious states. I even started to read a lot about hypnosis, (laughs) um, and all of these things, hypnosis, even sleep and dreams at the time, they were very esoteric. It was sort of charlatan science at that stage, and I think almost all of my colleagues and I are accidental sleep researchers.
- LFLex Fridman
(laughs)
- MWMatt Walker
You know, (laughs) no one, as I recall, in the classroom, when you're sort of five years old and the teacher says, "What would you like to be when you grow up?" You know, no one's putting their hand up and saying, "I would love to be a sleep researcher." (laughs) Um, and so when I was doing my PhD, I was trying to identify different forms of dementia very early on in the course, and I was using electrical brain wave recordings to do that, and I was failing miserably. It was a disaster, just no result after no result. And I used to go home to the doctor's residence with this sort of little igloo of journals that, at the weekend, I would sort of sit in and, uh, and read, and, (laughs) which I'm now thinking, "Do I really want to admit this?" 'Cause it sounds-
- LFLex Fridman
(laughs)
- MWMatt Walker
... like I had no social life, which I didn't.
- LFLex Fridman
Yeah.
- MWMatt Walker
I'm a social leper, but, and I started to realize that some parts of the brain were, um, sleep-related areas and some dementias were eating away those sleep-related areas. Other dementias would leave them untouched. And I thought, "Well, I'm doing this all wrong. I'm measuring my patients while they're awake." Instead, I should be measuring them while they're asleep. Started doing that, got some amazing results, and then I wanted to ask the question, "Is that sleep, um, disruption that my patients are experiencing as they go into dementia, maybe it's not a symptom of the dementia. I wonder if it's a cause of the dementia." And at that point, which was, (clears throat) (laughs) cough, cough, 20 years ago, um, no one could answer a very simple fundamental question, "Why do we sleep?" And I, at that time, didn't realize that some of the most brilliant minds in scientific history had tried to answer that question and failed, and at that point, I just thought, "Well, I'm going to go and do a couple of years of sleep research, and I'll figure out why we sleep, and then I'll come back to my patients and this question of dementia." And as I said, that was 20 years ago, and what I realized is that hard questions care very little about who asks them. They will meter out their lessons of difficulty all the same, and I was schooled (laughs) in the difficulty of the question, "Why do we sleep?" But in truth, 20 years later, we've had to upend the question. Rather than saying, "Why do we sleep?" And by the way, the, the answer then was that we sleep to cure sleepiness. (laughs) Which is like saying-
- LFLex Fridman
Right.
- MWMatt Walker
... "W- you know, we eat to cure hunger."
- LFLex Fridman
Yeah.
- MWMatt Walker
That tells you nothing about the physiological benefits of, of food. Same with sleep. Now, we've, uh, actually have to ask the question, is there any physiological system in the body, or any major operation of the mind that isn't wonderfully enhanced when we get sleep or demonstrably impaired when we don't get enough? And so far, for the most part, the answer seems to be no.
- LFLex Fridman
So far the answer seems to be no, so th- why,
- 6:35 – 15:06
Why do we sleep?
- LFLex Fridman
why does the body and the mind crave sleep then? Why do we sleep? D- how, um, can we begin to answer that question then?
- MWMatt Walker
So I think one of the ways that I think about this, or one of the answers that came to me is the following. The reason that we implode so quickly and so thoroughly with insufficient sleep is because human beings seem to be one of the few species that will deliberately deprive themselves of sleep for no apparent good reason, biological.
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
And what that led me then to was the following. Mother Nature as a consequence ... So no other species does what w- we do in that context. There are a few species that do undergo sleep deprivation but for very obvious, clear biological reasons. One is when they're in a condition of severe starvation. The second is when they're caring for their newborn. So, for example, killer whales will often deprive themselves. The female will go away from the pod, give birth, and then bring the calf back, and during that time, the mother will undergo sleep deprivation. And then the, the third one is during migration when birds are flying transoceanographic, 2-3,000 miles. But for the most part, it's never seen in the animal kingdom, which brings me back to the point, therefore, Mother Nature in the course of evolution has never had to face the challenge of this thing called sleep deprivation, and therefore she has never created a safety net in place to circumnavigate this common influence.
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
And there is a good example where we have, which is called the adipose cell, the fat cell, because during our evolutionary past, we had famine and we had feast, and Mother Nature came up with a very clever recipe, which is, "How can I store caloric credit so that I can spend it when I go into debt?" And the fat cell was born, brilliant idea. Where is the fat cell for sleep? (laughs) Where is that sort of banking chip for sleep? And unfortunately, we don't seem to have one because she's never had to face that challenge.
- LFLex Fridman
So even if there's not some kinda physics fundamental need for sleep, that, uh, physiologically or psychologically, the f- the fact is most organisms are built such that they need it, and then Mother Nature never built an extra mechanism for sleep deprivation. So it's interesting that why we sleep might not have a good answer- (laughs)
- MWMatt Walker
(laughs)
- LFLex Fridman
... but we need to sleep to be healthy is nevertheless true.
- MWMatt Walker
Yeah, and we have many answers right now. In some ways, the question of why we sleep was the wrong question too. It's, you know, what are the pluripotent many reasons we sleep? We don't just sleep for one reason because from an evolutionary perspective it is the most idiotic thing that you could imagine.
- LFLex Fridman
Yeah.
- MWMatt Walker
You know, when you're sleeping, you're not finding a mate, you're not reproducing, you're not caring for your young, you're not foraging for food, and worse still, you're vulnerable to predation. So on any one of those grounds (laughs) , but especially as a collective, sleep should've been strongly selected against in the course of evolution. But in every species that we've studied carefully to date, sleep is present.
- LFLex Fridman
Yeah, so it is important. So, like, you're, you're right. I, I think I've heard arguments from an evolutionary biology perspective that sleep is actually advantageous, you know, maybe like some kinda predator-prey relationships.
- MWMatt Walker
Yeah.
- LFLex Fridman
But you're saying, and it actually makes way more sense what you're saying, is it should've been selected against. Like, why close your eyes? (laughs)
- MWMatt Walker
Yeah. Why? Because ... And s- you know, there was an energy conservation hypothesis-
- LFLex Fridman
Yeah, right.
- MWMatt Walker
... for a while, which is that we need to essentially go into low battery mode, you know, power down because it's unsustainable, but in fact that actually has been blasted out the water because sleep is an incredibly active process. In fact, the difference between you just lying on the couch but remaining conscious versus you lying on the couch and falling asleep, it's only a savings of about 140, 150 calories. In other words, you know, you just go out and club another baby seal or whatever it was.
- LFLex Fridman
Yeah. (laughs)
- MWMatt Walker
And you wouldn't worry, you know? So there has to be much more to it than energy conservation, much more to it than sharing, you know, ecosystem space and time, much more to it than simply predator-prey relationships. If sleep really did ... And, you know, looking back, even very old evolutionary organisms like earthworms, millions of years old, they have periods where they're active and periods where they're passively asleep. It's called lethargicus. (laughs) And so what that in some ways suggested to me was sleep evolved with life itself on i- this planet, and then it has fought its way through heroically every step along the evolutionary pathway, which then leads to the sort of famous, um, sleep statement from a researcher, that if sleep doesn't serve an absolutely vital function or functions, then it's the biggest mistake the (laughs) evolutionary process has ever, ever made. And we've now realized Mother Nature didn't make a spectacular blunder with sleep.
- LFLex Fridman
Hmm. You've mentioned the idea of conscious states.Do you think of sleep as a fundamentally different conscious state than awakeness?
- MWMatt Walker
Mm-hmm.
- LFLex Fridman
And how many conscious states are there? So when you're into it, you're understanding of what the mind can do, do you think awake state, sleep state, or is there some kind of continuum, there's a complicated state transition diagram? Like, how do you think about this whole space?
- MWMatt Walker
I think about it as a state space diagram, and I think it's probably more of a continuum than we have believed it to be or suggested it to be. So we used to think absent of anesthesia that there were really three main, main states of consciousness. There was being awake, being in non-rapid eye movement sleep or non-dream sleep, and then being in rapid eye movement sleep or dream sleep, and those were the three states within which your brain could percolate and be conscious. Uh, you know, conscious during non-REM sleep is maybe a stretch to say, but I still believe there is plenty of consciousness there. I don't believe that, though, anymore, and the reason is because we can have daydreams, and we are in a very different wakeful state in those daydreams than we are when we are as we are now together, present and exteroceptively focused-
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
... rather than introceptively focused. And then we also know that as you are sort of progressing into those different stages of sleep, during non-REM sleep, you can also still dream. Depends on your definition of dreaming, but we seem to have some degree of dreaming in almost all-
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
... stages of sleep. We've also then found that when you are sleep-deprived, there, even individual brain cells will fall asleep-
- LFLex Fridman
Hm.
- MWMatt Walker
... despite the animal being, you know, behaviorally, from best we can tell, awake, individual brain cells and clusters of brain cells will go into a sleep-like state, and humans do this too. When we are sleep deprived, we have what are called micro sleeps, where the eyelid will partially close and the brain essentially falls, lapses into a state of sleep, but behaviorally, you seem to be awake, and the danger here is road traffic accidents. So these are the, what we call these sort of micro sleep, uh, events at the wheel. Now, if you're traveling at 65 miles an hour in a two-ton vehicle, you know, it takes probably around one second to drift from one lane to the next, and it takes two seconds to go completely off the road. So if you have one of these micro sleeps at the wheel, you know, it could be the last micro sleep that you ever have. Um, but I don't now see it as a set of, you know, very binary, distinct, you know, step function states. It's not a one or a zero. I see it more of a, as a
- 15:06 – 24:28
Computer vision for driver assistance
- MWMatt Walker
continuum, yeah.
- LFLex Fridman
S- so, I've for, for, uh, five, six years at MIT really focused on this human side of driving question, and one of the big concerns is the, uh, micro sleeps, drowsiness, these kinds of ideas. And one of the open questions was, is it possible through computer vision to detect ... or any kind of sensors. The nice thing about computer vision is you don't have to have direct contact to the person. Is it possible to detect increases in, uh, drowsiness? Is it possible to detect these kind of micro sleeps or actually just sleep in general?
- MWMatt Walker
Yeah.
- LFLex Fridman
Um, uh, among other things, like distraction, th- these are all words that have so many meanings, there's so many debates like-
- MWMatt Walker
Mm-hmm.
- LFLex Fridman
... like attention is a, is a whole nother one. Just because you're looking at something doesn't mean you're loading in the information. Just because you're looking away doesn't mean your peripheral vision can't pick up the important information. There's so many complicated vision science things there. Um, so I, I wonder if you could say something to ... Uh, you know, they say the eyes are the windows to the soul. Do you think, um, the eyes can reveal something about, uh, sleepiness, uh, through, uh, through computer vision, through, through just looking at the video of the face? And Andrew Huberman and I, your friend-
- MWMatt Walker
Oh.
- LFLex Fridman
... have talked about this.
- MWMatt Walker
He's a brilliant man. Brilliant man.
- LFLex Fridman
So I would love to work on this, uh, together. It's a-
- MWMatt Walker
You should do.
- LFLex Fridman
It's a fascinating problem. But drowsiness is a tricky one. So there's what kind of information? There's, uh, blinking and there's eye movement, and those are the ones that can be picked, uh, up with computer vision. Do you think those are signals that could be used to say something about where we are in this continuum?
- MWMatt Walker
Yeah, I do, and I think there are a number of other features too. I think, um, you know, aperture of eye, so in other words, partial closures, full closures, um, duration of those closures, duration of those partial closures of the eyelid. Um, I think there may be some information in the pupil as well, because as we're transitioning between those states ch- there are changes in what's called the automatic nervous system, or technically it's called the autonomic nervous system, part of which will control your pupillary size.
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
So I actually think that there is probably a, a wealth of information. When you combine that probably with aspects of steering angle, steering maneuver-
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
... and if you can sense the pressure on the pedals as well-
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
... my guess is that there is some combinatorial feature that creates a phenotype of you are starting (laughs) to fall asleep. And as the autonomous controls develop, the, it's time for them to kick in. Some manufacturers, auto manufacturers sort of have something-... beta version, maybe an alpha version of (laughs) this already starting to come online, where they have a little camera in the wheel that I think tries to look at some features.
- LFLex Fridman
Almost everybody doing this, and it's very alpha.
- MWMatt Walker
(laughs)
- LFLex Fridman
(laughs) . Uh, so, uh, you know, the thing that you currently have is when people have that in their car, there's a coffee cup or something that comes up that you might be sleepy. The, the primary signal that they're comfortable using is, uh, steering wheel reversals. So, so basically using your interaction with the steering wheel and how much you're interacting with it as a sign of sleepiness. So if you have to constantly correct the car-
- MWMatt Walker
Yeah.
- LFLex Fridman
... that's a sign of, like, you starting to drift into microsleep. I think that's a very, very crude signal. It's probably a powerful one. There's a whole nother component to this, which is it seems like it's so driver and subject dependent. Um, the, the, how our behavior changes as we get sleepy and drowsy seems to be-
- MWMatt Walker
Right.
- LFLex Fridman
... different in complicated, fascinating ways, where you can't just use one signal. It's kind of like what you were saying, there has to be a lot of different signals that you should then be able to combine. The hope is there's, uh, the search is for, like, universal signals that are pretty damn good for, like, 90% of people.
- MWMatt Walker
Yeah. But I don't think we need to take necessarily quite that approach. I think what we could do in some clever fashion is using the individual. So what you and I are perhaps suggesting here is that there is a, an array of features that we know provide information that is sensitive to whether or not you're falling asleep at the wheel. Some of those, let's say that there are ten of them. You know, for me, seven of them are the cardinal features.
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
For you, however, you know, six of them, and they're not all the same, sort of overlapping, are those for you. I think what we need is algorithms that can firstly understand when you are well-slept. So let's say that people have sleep trackers at night, and then your car integrates that information and-
- LFLex Fridman
That would be amazing.
- 24:28 – 32:34
Consciousness is fundamental
- LFLex Fridman
how fundamental do you think is consciousness to the human mind? I ask this from almost like a robotics perspective. So, in your study of sleep, do you think the, the hard question of consciousness, that it feels like something to be us, is that like a nice little feature, like a, like a, like a quirk of our mind, or is it somehow fundamental? Because sleep feels like we take, we take a s- step out of that consciousness a little bit. So, from all your study of sleep, do you think consciousness is like deeply part of who we are, or is it just a nice trick?
- MWMatt Walker
I think it's a deeply embedded feature that I can imagine has a whole panoply of biological benefits. But to your point about sleep, what is interesting if you do a lot of dream research, and we've done some, it's very, very rare, at all in fact, for you to end up becoming someone other than who you are in your dreams. Now, you can have third-person perspective dreams where you can see yourself in the dream as if you're sort of, you know, you've risen above your, y- your physical being. But for the most part, it's very rare that we lose our sense of conscious self. And maybe I'm sort of doing a sleight of hand because it's really, what I'm saying is it's very rare that we lose our sense of who we are-
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
... in dreams. We never do. Now, that's not to suggest that dreams aren't utterly bizarre and, uh, I mean, you know, when you slept last night, which I know, um, may have been-
- LFLex Fridman
(laughs)
- MWMatt Walker
... p- perhaps a little less than, than me. But when you went into dreaming, you know, you became flagrantly psychotic.
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
And there are five essentially good reasons. Firstly, you started to see things which were not there, so you were hallucinating. Second, you believed things that couldn't possibly be true, so you were delusional. Third, you became confused about time and place and person, so you're suffering from what we would call disorientation. Fourth, you have wildly fluctuating emotions, something that, um, psychiatrists will call being affectively labile.
- LFLex Fridman
(laughs)
- MWMatt Walker
And then how wonderful that you woke up this morning and you forgot most, if not all, of that dream experience, so you're suffering from amnesia.
- LFLex Fridman
(laughs)
- MWMatt Walker
If you were to experience any one of those five things while you were awake-
- LFLex Fridman
Yeah.
- MWMatt Walker
... you would probably be seeking psychological-
- LFLex Fridman
Yeah.
- MWMatt Walker
... help. But what ... So, I place that as a backdrop against your astute question-
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
... because despite all of that psychosis, there is still a present self-
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
... nested at the heart of it. Meaning that I think it's very difficult for us to abandon our conscious sense of self. And if it's that hard, you know, it's the old adage in some ways that you can't outrun your shadow.
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
But here it's more of a philosophical question which is about the conscious mind and what the state of consciousness actually means in a human being.
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
So, I think that that, to me, you can ... You become so dislocated from so many other rational ways of waking consciousness, but one thing that won't go away, that won't get perturbed or sort of, m- you know, manacled, is this: your sense of conscious self.
- LFLex Fridman
Yeah, that's a strong sign that consciousness is fundamental to the human mind, um, or we're just creatures of habit, we've gotten used to having consciousness.
- MWMatt Walker
(laughs)
- LFLex Fridman
Maybe it just takes a lot of, uh, either chemical substances or a lot of, uh, like mental work to escape that.
- MWMatt Walker
I mean, it's like trying to launch a rocket. You know, the energy that has to be put in to create escape velocity from the gravitational pull of this thing called Planet Earth is immense.
- LFLex Fridman
Yeah.
- MWMatt Walker
Well, the same thing is true for, uh, for us to abandon our sense of conscious self.
- 32:34 – 35:01
Lex on human to robot connection
- MWMatt Walker
So...
- LFLex Fridman
Yeah. I think of human consciousness, or consciousness in general, as this magic, um, superpower that allows us to deeply experience the world, and just as you're saying, I don't think that superpower has to take the exact flavor as humans have. That's my love for robots. I would love to add the ability to robots that can experience the world and other humans, uh, deeply. I'm humbled by the fact that that idea does not necessarily need to look anything like how humans experience the world, but there's a dance of, um, human to robot connection, the same way human to dog or human to cat connection, that there's a, there's a, there's a magic there to that interaction, and I'm not sure how to create that magic, but it's a worthy effort. I also love, just exactly as you said, on the question of consciousness or engineering consciousness, the fun thing about this problem is it s- seems obvious to me that 100 years from now, no matter what we do today, uh, people, if we're still here, will laugh at how silly our notions were. So like, it's almost impossible for me to imagine that we will truly solve this problem fully, uh, in my lifetime. (laughs)
- MWMatt Walker
(laughs)
- LFLex Fridman
And, and more than that, everything we'll do will be silly 100 years from now, but it's still, uh, a w- that makes it fun to me, because it's like you have the full freedom to not even be right. (laughs) Just to try.
- MWMatt Walker
Yeah.
- LFLex Fridman
Just to try is freedom. And, uh, and I, that's how I see...
- MWMatt Walker
Can you get me that T-shirt, please? (laughs)
- LFLex Fridman
(laughs)
- MWMatt Walker
I love that.
- LFLex Fridman
So, a- and, you know, human-robot interaction is fascinating because it's like, it's like watching dancing. I've been, uh, dancing tango recently, and just it's like there is no goal. The goal is to create something magical.
- MWMatt Walker
Mm-hmm.
- LFLex Fridman
And, uh, whether consciousness, or emotion, or elegance of movement, all of those things, uh, aid in the creation of the magic, and it's a free, it's art, it's an art form to explore how, how to make that, um, how to create that in a way that's compelling.
- MWMatt Walker
Yeah, I love the, the line in Scent of a Woman with Al Pacino, where he's speaking about the tango and he says, "Really, it's just freedom that if you get tangled up, you just keep tangoing on."
- 35:01 – 46:42
Scent of a Woman is better than "John Wick"
- MWMatt Walker
- LFLex Fridman
I still to this day, I think, uh, well, first or second time I talked to Joe Rogan on his podcast, I said, we got into this heated argument about whether, uh, um, Scent of a Woman is a better movie than John Wick, (laughs) because it's, it's one of my favorite movies for many reasons. One is-
- MWMatt Walker
Which one? Scent of a Woman?
- LFLex Fridman
Se- Scent of a Woman. Uh, partially-
- MWMatt Walker
I didn't know that, by the way. I was just gonna... (laughs)
- LFLex Fridman
(laughs) You just, you tossed that out there.
- MWMatt Walker
Yeah, I didn't know if you would actually know of the movie.
- LFLex Fridman
Oh, awesome. Awesome.
- MWMatt Walker
Yeah.
- LFLex Fridman
No, yeah, I said, "I love the tango scene. I love Al Pacino's performance. It's a wonderful movie." (laughs) Then Joe, Joe was saying John Wick is better, so we, to this day, argue about this.
- MWMatt Walker
I think it depends in, on what conscious state you're in...
- LFLex Fridman
Yes, sir.
- MWMatt Walker
... that you would be ready and receptive to, but, um, Scent of a Woman, eh, I think it has one of the best monologues at the end of the movie that has ever been written or at least performed, uh...
- LFLex Fridman
When Al Pacino def- defends the-
- MWMatt Walker
That's correct.
- LFLex Fridman
... the young- the younger... Yeah, I, uh, I often think about that. There's been times in my life, uh, I don't know about you, where I wish I had an Al Pacino in my life.
- MWMatt Walker
(laughs)
- LFLex Fridman
Where, um...... integrity is really important in this life.
- MWMatt Walker
It is.
- LFLex Fridman
And sometimes, you find yourself in places where there's pressure to sacrifice that integrity, and y- you want, uh, what is it, Lieutenant Colonel, or whatever he was-
- MWMatt Walker
(laughs) Slade.
- LFLex Fridman
... to come in (laughs) -
- MWMatt Walker
(laughs)
- LFLex Fridman
... to come in, uh, on your side and, and scream at everyone and say, "What the hell are we doing here?"
- MWMatt Walker
Being, you know, unfortunately, British, and sort of having that slightly, um, awkward sort of Hugh Grant gene, it's-
- LFLex Fridman
(laughs)
- MWMatt Walker
... it's very, very (laughs) ... we're at the opposite end of the spectrum of the remarkable feat of, uh, Al Pacino at the- the end of that scene, but, um, and yeah, integrity is, um, it's a, it's a challenging thing, and I value it much, and I think, um, it can take 20 years to build a reputation and two minutes to lose it.
- LFLex Fridman
Yeah.
- MWMatt Walker
And there is nothing more that I value than, than integrity, and, you know, if I'm ever wrong about anything, I truly don't want to be wrong for any longer than I have to be. Um, you know, that's what being, in some ways, a scientist is. You're- you're just driven by truth, and the irony, relative to something like mathematics, is that, in science, you never find truth. What- all you do in science is you discount the things that are likely to be untrue, leaving only the possibility of what could be true.
- LFLex Fridman
Yeah.
- 46:42 – 1:12:26
Distinction between coffee and caffeine
- LFLex Fridman
I'm a big fan of coffee and caffeine, and I've been, especially in the last few days, consuming a very large amount, and I'm cognizant of the fact that, um, my body is affected by caffeine different than the anecdotal information that other people tell me. I seem to be not at all affected by it. It's almost, um... It- it feels like more like a ritual than it is a, a chemical boost to my performance. Like, I can drink several cups of coffee right before bed and just knock out anyway. I'm not sure if it's, uh, biological, chemical, or it has to do with just the fact that I'm cos- consuming huge amounts of caffeine. All that to say, uh, what do you think is the relationship between coffee and sleep? Caffeine and sleep? If there's an interesting distinction there.
- MWMatt Walker
There is a distinction. So, I think the first thing to say, which is going to sound strange coming from me, is drink coffee. (laughs) Um, the health benefits associated with drinking coffee are really quite well-established now, um, but I think the, the counterpoint to that... Well, firstly, the dose and the timing make the poison, and I'll perhaps come back to that-
- LFLex Fridman
Yes.
- MWMatt Walker
... in just a second. But for coffee, it's actually not the caffeine.
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
So, you know, a lot of people ha- have asked me about this rightful paradox between the fact that sleep provides all of these incredible health benefits, and then coffee, which can have a deleterious-... impact on your sleep, has (laughs) a whole collection of health benefits, many of them Venn diagram overlapping with those that sleep provides. How on earth can you reconcile those two? And the answer is that... Well, the answer is very simple, it's called antioxidants. That it turns out that for most people in Western civilization, because of diet not being quite what it should be, the major source through which they obtain antioxidants is the coffee bean. So, the, the humble coffee bean has now been asked to carry the astronomical weight of serving up the large majority of people's antioxidant needs.
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
And you can see this if, for example, you look at the health benefits of decaffeinated coffee. It has a whole constellation of really great health benefits too. So, it's not the caffeine. And that's why I liked what you said-
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
... this sort of separation of church and state between coffee-
- LFLex Fridman
(laughs)
- MWMatt Walker
... and caffeine. It's not the caffeine, it's the coffee bean itself that provides those health benefits. But coming back to how it impacts sleep, it impacts sleep in probably at least three different ways. The first is that, for most people, caffeine can make it, obviously, a little harder to fall asleep. Caffeine can make it harder to stay asleep. But let's say that you are one of those individuals, and I think you are, and you can say, "Look, I can have three or four espressos with dinner and I fall asleep just fine, and I stay asleep soundly across the night, so there's no problem." Th- the downside there is that, even if that is true, the amount of deep sleep that you get will not be as deep, and so you will actually lose somewhere between 10 to 30% of your deep sleep if you drink caffeine in the evening.
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
So, to give you some context, to, to drop your deep sleep by, let's say, 20%, I'd probably have to age you by 15 years, or you could do it every night with a cup of coffee. I think the fourth component that is perhaps less well-understood about coffee is its timing, and that's why I was saying the timing and the dose make the poison. The dose, by the way, once you get past about three cups of coffee a day, the health benefits actually start to turn down in the opposite direction.
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
So, there is a U-shaped function. It's sort of a, you know, the Goldilocks syndrome, not too-
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
... little, not too much, just the right amount. The second component is the timing, though. Caffeine has a half-life of about, um, five to six hours, meaning that after five to six hours, 50% of that, on average, for the average adult, is still in the system, which means that it has a quarter life of 10 to 12 hours. So, in other words, if you have a coffee at noon, a quarter of that caffeine is still circulating in your brain at midnight. So, having a cup of coffee at noon, one could argue is the equivalent of tucking yourself into bed at midnight, and before you turn the light out-
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
... you swig a quarter of a cup of coffee. But that doesn't still answer your question as to why are you so immune. So, I'm someone who is actually, unfortunately, very sensitive to caffeine, and if I have, you know, even two cups of coffee in the morning, um, I, I don't sleep as well that night. And I find it miserable because I love the smell of coffee, I love the routine, I love the ritual. I think I would love to be invested in it. It's just terrible for my sleep, so I switch to decaf. There is a difference from one individual to the next, and it's controlled by a set of liver enzymes called cytochrome P450 enzymes. And there is a particular gene that, if you have a different sort of version of this gene, it's called CYP1A2, that gene will determine the speed of the clearance of caffeine from your system.
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
Some people will have a version of that gene that is very effective and efficient at clearing that caffeine, and so their half-life could be as short as two hours rather than five to six hours. Other people, uh, hands up, Matt Walker, um, have a version of that gene that is not very effective at (laughs) clearing out the, uh, the caffeine, and therefore, their half-life sort of sensitivity could be somewhere between, you know, eight to nine hours.
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
So, we understand that there are individual differences, but overall, I guess, the, the top line here is drink coffee, um, and understand that it's not the caffeine, it's the coffee that's the benefit, and the dose makes the poison.
- LFLex Fridman
Is there some aspect to it that's it's like a muscle in terms of the... or the combination of, of letters and numbers-
- MWMatt Walker
Mm-hmm.
- LFLex Fridman
... that you just said? Is there some aspect that if, um, I can improve the quarter life, the half-life c- could decrease that number if I just practice?
- MWMatt Walker
(laughs)
- LFLex Fridman
Like, I drink a lot of coffee, so, so, like, habit, uh, uh, alters how your body's able to get rid of the caffeine.
- MWMatt Walker
Not how the body is able to get rid of the caffeine, but, uh, it does alter how sensitive the body is to the caffeine. And it's not at the level of the enzyme degrading the caffeine. It's at the level of the receptors that caffeine will act upon.
- 1:12:26 – 1:26:19
The science of 'sleeping on it'
- MWMatt Walker
- LFLex Fridman
(laughs) Yeah, so in terms of...... this line between learning and thinking through a new thing, uh, that seems to be deeply, uh, connected. There's this, um, legendary engineer, named Jim Keller, who keeps yelling at me about this, he says it's very effective, he likes to f- for difficult problems, before bed, think about that difficult problem. We're not talking about like drama at work or all that kind of stuff, no, like a scientific, for him, engineering problem. He likes to, like, intensely think about it as to prime his mind-
- MWMatt Walker
Yes.
- LFLex Fridman
... before sleeping, then go to sleep, and then, uh-
- MWMatt Walker
Yeah.
- LFLex Fridman
... he finds that, uh, the next day, he's, he's able to think much clearer, and there's new ideas that come, but also just, I guess, it's more well-integrated. Um, and sometimes during the process of, uh, like he's able to, like, wake up and, like, see, see new insights-
- MWMatt Walker
That's right.
- LFLex Fridman
... if he's deeply, sort of, aggressively thinking through a problem. (laughs) So, he-
- MWMatt Walker
And there's, there's many scientific, you know, demonstrations of this, you know, the- Mendeleev with the periodic table of elements, you know, he was trying for months to understand... I mean talk about a, an ecumenical problem of epic proportions. Here's your question today, (laughs) you have to understand how all of the known elements in the universe fit together-
- LFLex Fridman
Yeah.
- MWMatt Walker
... in a logical way. Good luck, take care. It was non-trivial at the time, and he would try and try. He was so obsessed with it, he created playing cards with all of the different elements on, and then he would go on these long train journeys around Europe, and he would just f- sort of, deal these cards in front of them and he would shuffle them, shuffling and shuffling, and he would just try to see if he could find what the answer was.
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
And then, so the story goes, you know, he fell asleep and he had a dream, and in that dream, you know, all of these elements started to dance and play around, and they snapped into a logical grid-
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
... you know, atomic weight, et cetera, et cetera. And it wasn't his waking brain that solved the problem, it was his sleeping brain that solved the impenetrable problem that his waking brain could not. And there's been count- you know, even in the arts and in music, some wonderful dreams, you know, Frankenstein, Mary Shelley's epic Gothic novel, came to her in a dream at Lord Byron's home. Um, and then we've got, you know, Paul McCartney, um, yesterday the song came to him in a dream. He was in, uh, filming, um - gosh what was the movie? Um, I don't recall it. I should be shocked because I'm from Liverpool myself.
- LFLex Fridman
(laughing)
- MWMatt Walker
Um, and, but he was on Wimpole Street, in London-
- LFLex Fridman
Yes.
- MWMatt Walker
... um, and filming, and they, he came up with that song, the melody, um, in his sleep. Not to be outdone by The Beatles, and by the way, Let It Be, um, also came from a dream-
- LFLex Fridman
Mm-hmm.
- MWMatt Walker
... that McCartney had. People usually give it, you know, religious overtones, you know, "Mother Mary comes to me speaking words of wisdom, let it be." E- if you've ever asked who Mother Mary is, it's not the, you know, the biblical content, it's his, his mother, it's, it's, it's Mary McCartney, (laughs) and she came to him in a dream, and gifted him the song. But the best story I've heard is, um, not to be outdone by The Beatles, The Stones-
- LFLex Fridman
(laughs)
- MWMatt Walker
... um, Keith Richards-
- LFLex Fridman
Yeah.
- MWMatt Walker
... uh, who I think once was suggested that... Who was it? It was a comedian who was saying that in an interview with Rolling Stone, Keith Richards suggested or inferred that young kids should not do drugs. And they said-
- LFLex Fridman
(laughing)
- MWMatt Walker
... "Well, look-"
- LFLex Fridman
Yeah.
- MWMatt Walker
"... young kids can't do drugs because you've done all of the drugs."
- LFLex Fridman
All of them, yeah. (laughing)
- 1:26:19 – 1:51:23
Lex on his sleeping schedule
- LFLex Fridman
maybe this is me trying to justify my lifestyle to you, but, uh, Dr. Seuss said, "You know you're in love when you can't fall asleep because reality is finally better than your dreams."
- MWMatt Walker
(laughs) Mm-hmm. I love that quote too.
- LFLex Fridman
(laughs) Okay. My sleeping, uh, schedule is, uh, complicated, and it has to do primarily with the fact that I love, uh, basically everything that I do, and that love takes a form that may not appear to be love from the external observer perspective, 'cause it's often includes struggle, it often includes something that looks like stress, even though it's not stress. It's like this excitement, it's this-
- MWMatt Walker
(laughs)
- LFLex Fridman
... turmoil and chaos of passion, of struggling with a problem, of being sad and down, uh, to the point even depressed of how difficult the problem is, the disappointment that the last few weeks and months have been a failure and, uh, self-doubt, all that mix, but I, I, I love it. And a part of that is sometimes staying up all night, working on a thing I'm really passionate about, and that means sleep schedules that are just like, you know, uh, sometimes sleeping during the day, sometimes very often sleeping very little, but taking naps that are like an hour or two hours or so on, that kind of weird chaos. And, and-
- MWMatt Walker
Yeah.
- LFLex Fridman
Now, I'll also s- to try to give, give myself backup.
- MWMatt Walker
(laughs)
- LFLex Fridman
I was trying to like, uh, research yesterday, is anybody else productive while like this? And there is, of course, a lot of anecdotal evidence, and some of it, um, could be just narratives that people have told to the public when in reality they sleep way more, but there's a bunch of people that, uh, you know, have not, are f- are famous for not sleeping much.
- MWMatt Walker
Right.
- LFLex Fridman
So, uh, on the topic of naps, uh, this, I read this a long time ago and I, I checked this. Churchill was big on big naps.
- MWMatt Walker
Mm-hmm.
- LFLex Fridman
And is actually just reading more about Winston Churchill's sleep schedule is very much like mine. So, I basically wanna give myself the opportunity to, at night, to stay up all night if I want to.
Episode duration: 2:48:17
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