The Glymphatic System and Sleep's Role in Brain Health

My conversation with Matthew Walker, PhD on faculty at UC Berkeley where he is a professor of neuroscience and psychology, the founder and director of the Center for Human Sleep Science, and has a long history of seminal contributions on sleep science and health.

Audio File (also downloadable at Apple Podcast and Spotify)

“Sleep is a non-negotiable

biological state required for the maintenance of human life . . . our needs

for sleep parallel those for air, food, and water.”—Grandner and Fernandez

Eric Topol (00:07):

Hello, it's Eric Topol with Ground Truths, and I am really delighted to welcome Matt Walker, who I believe has had more impact on sleep health than anyone I know. It's reflected by the fact that he is a Professor at UC Berkeley, heads up the center that he originated for Human Sleep Science. He wrote a remarkable book back in 2017, Why We Sleep, and also we'll link to that as well as the TED Talk of 2019. Sleep is Your Superpower with 24 million views. That's a lot of views here.

Matt Walker:

Striking, isn't it?

Eric Topol:

Wow. I think does reflect the kind of impact, you were onto the sleep story sooner, earlier than anyone I know. And what I wanted to do today was get to the updates because you taught us a lot back then and a lot of things have been happening in these years since. You're on it, of course, I think you have a podcast Sleep Diplomat, and you're obviously continued working on the science of sleep. But maybe the first thing I'd ask you about is in the last few years, what do you think has been, are there been any real changes or breakthroughs in the field?

What Is New?

Matt Walker (01:27):

Yeah, I think there has been changes, and maybe we'll speak about one of them, which is the emergence of this brain cleansing system called the glymphatic system, but spreading that aside for potential future discussion. I would say that there are maybe at least two fascinating areas. The first is the broader impact of sleep on much more complex human social interactions. We think of sleep at maybe the level of the cell or systems or whole scale biology or even the entire organism. We forget that a lack of sleep, or at least the evidence suggests a lack of sleep will dislocate each other, one from the other. And there's been some great work by Dr. Eti Ben Simon for example, demonstrating that when you are sleep deprived, you become more asocial. So you basically become socially repellent. You want to withdraw, you become lonely. And what's also fascinating is that other people, even they don't know that you sleep deprived, they rate you as being less socially sort of attractive to engage with.

Matt Walker (02:35):

And after interacting with you, the sleep deprived individual, even though they don't know you're sleep deprived, they themselves walk away feeling more lonely themselves. So there is a social loneliness contagion that happens that a sleep deprived lonely individual can have almost a viral knock on effect that causes loneliness in another well-rested individual. And then that work spanned out and it started to demonstrate that another impact of a lack of sleep socially is that we stop wanting to help other people. And you think, well, helping behavior that's not really very impactful. Try to tell me of any major civilization that has not risen up through human cooperation and helping. There just isn't one. Human cooperative behavior is one of our innate traits as homo sapiens. And what they discovered is that when you are insufficiently slept, firstly, you don't wish to help other people. And you can see that at the individual level.

Matt Walker (03:41):

You can see it in groups. And then there was a great study again by Dr. Eti Ben Simon that demonstrated this at a national level because what she did was she looked at this wonderful manipulation of one hour of sleep that happens twice a year to 1.6 billion people. It's called daylight savings time at spring. Yeah, when you lose one hour of sleep opportunity. She looked at donations across the nation and sure enough, there was this big dent in donation giving in the sleepy Monday and Tuesday after the clock change. Because of that sleep, we become less willing to empathetically and selflessly help other individuals. And so, to me I think it's just a fascinating area. And then the other area I think is great, and I'm sorry I'm racing forward because I get so excited. But this work now looking at what we call genetic short sleepers and sort of idiots like me have been out there touting the importance of somewhere between seven to nine hours of sleep.

Matt Walker (04:48):

And once you get less than that, and we'll perhaps speak about that, you can see biological changes. But there is a subset of individuals who, and we've identified at least two different genes. One of them is what we call the DEC2 gene. And it seems to allow individuals to sleep about five hours, maybe even a little bit less and show no impairment whatsoever. Now we haven't tracked these individuals across the lifespan to truly understand does it lead to a higher mortality risk. But so far, they don't implode like you perhaps or I would do when you are limited to this anemic diet of five hours of sleep. They hang in there just fine. And I think philosophically what that tells me, and by the way, for people who are listening thinking, gosh, I think I'm probably one of those people. Statistically, I think you are more likely to be struck by lightning in your lifetime than you are to have the DEC2 gene. Think about what tells us, Eric. It tells us that there is a moment in biology in the evolution of this thing called the sleep physiological need that has changed such that mother nature has found a genetic way to ZIP file sleep.

Matt Walker (06:14):

You can essentially compress sleep from seven to nine hour need, down to five to six hour need. To me, that is absolutely fascinating. So now the race is on, what are the mechanisms that control this? How do we understand them? I'm sure much to my chagrin, society would like to then say, okay, is there a pill that I can take to basically ZIP file my own sleep and then it becomes an arms race in my mind, which is then all of a sudden six hours becomes the new eight hours and then everyone is saying, well, six hours is my need. Well I'll go to four hours and then it's this arms race of de-escalation of sleep. Anyway, I'm going on and on, does that help give you a sense of two of the what I feel the more fascinating areas?

Eric Topol (07:01):

Absolutely. When I saw the other recent report on the short sleep gene variant and thought about what the potential of that would be with respect to potential drug development or could you imagine genome editing early in life that you don't need any sleep? I mean crazy stuff.

Matt Walker (07:19):

It was amazing.

Glymphatics and Deep Sleep

for more, see previous Ground Truths on this topic

Eric Topol (07:22):

No, the mechanism of course we have to work out and also what you mentioned regarding the social and the behavior engagement, all that sort of thing, it was just fascinating stuff. Now we touched on one thing early on to come back to the glymphatics these channels to get rid of the waste metabolites from the brain each night that might be considered toxic metabolites. We've learned a lot about those and of course there's some controversy about it. What are your thoughts?

Matt Walker (07:55):

Yeah, I think there's really quite comprehensive evidence suggesting that the brain has this cleansing system like the body has one the lymphatic system, the brain has one the glymphatic system named after these glial cells that make it up. And I think there's been evidence from multiple groups across multiple different species types, from mouse models all the way up to human models suggesting that there is a state dependent control of the brain cleansing system, which is a fancy way of saying if you are awake in light NREM, deep NREM or perhaps you're just quiet and you are resting in your wakefulness, the glymphatic system is not switched on at the same rate across all of those different brain states. And I think the overwhelming evidence so far using different techniques in different species from different groups is that sleep is a preferential time. It's not an exclusive time, it's a preferential time when that brain cleansing system kicks into gear because as some people have, I think argued, and you could say it's hyperbolic, but wakefulness is low level from a biochemicals perspective, it's low level brain damage and sleep is therefore your sanitary salvation that combat that biochemical cascade.

Matt Walker (09:15):

So in other words, a better way of putting it would be, sleep is the price that you pay for wakefulness in some ways. And I think there was a recent controversial study that came out in 2022 or 2023, and they actually suggested quite the opposite. They said using their specific imaging methods, they found that the sort of clearance, the amount of cerebral spinal fluid, which is what washes through the brain to cleanse the toxins, the rate of that flow of cerebral spinal fluid was highest during wakefulness and lowest during deep NREM sleep, the exact opposite of what others have found. Now, I think the defendants of the glymphatic sleep dependent hypothesis pushed back and said, well, if you look at the imaging methods. Firstly, they’re nonstandard. Secondly, they were measuring the cerebral spinal flow in an artificial way because they were actually perfusing solutions through the brain rather than naturally letting it flow and therefore the artificial forcing of fluid changed the prototypical result you would get.

Matt Walker (10:27):

And they also argued that the essentially kind of the sampling rate, so how quickly are you taking snapshots of the cerebral spinal fluid flow. Those were different and they were probably missing some of the sleep dependent slow oscillations that seemed to sort of drive that pulsatile flow. Honestly, I think that paper was still very well done, and I still think there is right now, I would still cleave to the majority of overwhelming evidence considering it's not just from one group in one species, but across multiple species, multiple groups. And I think it's nevertheless a weight of burden that has pushed back. And my sense right now, I used to think and cleaves to the notion that it was a sleep expressly selective process. Now I don't think that that's the case anymore. I think that the glymphatic system is a dynamic system, but it's always looking for the opportunity to go into cleansing mode. And you can kind of go into almost like a low battery mode when you are awake, but in quiet rest. And I think that can drive some already early clearance from the brain and then when you go into sleep, it's like powering your phone off entirely. It truly gets the chance to cleanse and reboot the biochemical system. But I think it's really interesting. I think there's a lot of work still yet to be done. It's not quite as case closed as we used to think.

Eric Topol (12:03):

Yeah, I mean first of all, it's great that you straighten out the controversy because that's exactly what I was referring to. And secondly, as you also pointed out, the weight of the evidence is that it's a sleep dependent phenomena, particularly during flow wave deep sleep is at least what I've seen.

Matt Walker (12:21):

Yes.

Eric Topol (12:22):

What's also interesting, your point about it being dynamic, which fascinating, there was a paper in my field of cardiology, people with atrial fibrillation had less active glymphatic, less clearance which was really interesting. And then the other finding that's also noteworthy was that Ambien made things worse. What do you think about that?

We Are An Embodied Organism

Matt Walker (12:45):

I think it's really interesting, and just to come back to your point about the AFib paper, what we know is that this cleansing system in the brain does seem to track the big slow brainwaves of deep slow wave sleep, but it's not only tracking the big slow brainwaves. If anything, there's something to do with the cardiorespiratory cycle, the respiration rate and the cardiac signal that may actually sink with the brainwaves. And it's essentially a cardiorespiratory neurophysiological coupling, which is a lot of ways, which is to say heart, lungs and brain coupled together. And it's the coupling of the cardiorespiratory slow oscillations that drive these pulsatile fluid mechanical, it's literally a hydro mechanical, hydro meaning cerebral spinal fluid push and pull in and out of the system drawing those metabolites out. So ago, if you have a disrupted either cardiac or respiratory or neurophysiological signal, no wonder the glymphatic system isn't going to work as efficiently.

Matt Walker (14:00):

I think that's a beautiful demonstration of the hemineglect that people like me who study sleep largely from the neck upwards would miss. But if you think about sleep is not just for the brain, it's for the body and it's not just for the body, it's for the brain. And we're an embodied organism. We study the organism in silos, neurology, psychiatry, cardiology, respiratory, but they all interact. And so, I think what's lovely about your example is the reminder that if you don't study the body in this study of the glymphatic system, you could miss out a profound explanation that possibly accounts for the head scratching, I don't know why we're getting this result. So that's a long way to come back to it. But the same group that was the pioneer in the discovery of the glymphatic system led by Maiken Nedergaard at the University of Rochester.

In SUPER AGERS, p. 57. SRI-sleep regulatory index

Sleep Medications

Matt Walker (15:01):

She has gone on to then look to say, well, if this is a sleep dependent process of brain cleansing during deep sleep, what about sleeping pills because so many people are either taking or are addicted to sleeping pills. And we've gone through, we’re in the era of web 3.0 with sleeping pills, we started off web 1.0 which were the benzos, the kind of temazepam, diazepam, lorazepam. Then we went to web 2.0, which was sort of the Ambien (zolpidem), Lunesta, Sonata. And what was common about those two classes of drugs is that they both went after something called the GABA receptor in the brain, which is this major inhibitory receptor in the brain. And essentially, they were called sedative hypnotics because they sedated your cortex. And when you take an Ambien and not going to argue you're awake. You're clearly not awake, but to argue you're a naturalistic sleep, if you look at this, physiology is an equal fallacy.

Matt Walker (16:01):

They made this interesting experimental hypothesis that when you take Ambien, you sleep longer and based on how you score deep sleep, it would seem as though Ambien increases the amount of minutes that you spend in deep sleep. But if you look at the electrical signature during that “increased deep sleep” it's not the same. Ambien takes a big bite. There's a big dent out of the very slowest of the slow brainwaves, and it's the slowest of the slow brainwaves that drive the glymphatic system. So what they found was that when you take Ambien or you give mice Ambien. Yes, they sleep longer, they seem to have more deep sleep, but the brain cleansing mechanism seem to be reduced by anywhere between 30-40%, which is counterintuitive. If you are sleeping more and you're getting more deep sleep and the glymphatic system is active during deep sleep, you should get greater cleansing of the brain.

Matt Walker (17:05):

Here they found, yes, the drug increased sleep, particularly deep sleep, but it empowered the cleansing of the brain system. Now, have we got evidence of that in humans yet? No, we don't. I don't think it's far away though, because there was a counter study that brings us onto web 3.0. There's a new class of sleep medications. It's the first class of medications that have actually been publicly advocating for, they're called the DORAs drugs, and they are a class of drugs and there's three of them that are FDA approved right now. DORA stands for dual orexin receptor antagonists, which means that these drugs go in there and they block the action of a chemical called orexin. What is orexin? Orexin is the volume button for wakefulness. It dials at wakefulness, but these drugs come into your system and unlike the sedative sort of baseball bat to the cortex, which is Ambien, these drugs are much more elegant.

Matt Walker (18:11):

They go down towards the brainstem and they just dial down the volume on wakefulness and then they step back, and they allow the antithesis of wakefulness to come in its place, which is this thing called naturalistic sleep. And people sleep longer. So as a scientist, you and I perhaps skeptics would then say, well, so you increase sleep, and I have four words for you. Yes, and so what. Just because you increase sleep, it doesn't mean that it's functional sleep. It could just be like the old notion of junk DNA, that it's epiphenomenal sleep. It's not functional sleep. There was a study out of WashU and they took 85-year olds and above and they gave them one of these DORAs drugs. It's a drug called Belsomra, it’s a play on good sleep or beautiful sleep, chemical named suvorexant and randomized placebo control. What they found is that when they took the drug, yes, these older adults slept longer, they had more deep sleep, but then what they did was clever. Before and after the night of sleep, they drew blood because we can now measure markers of β-amyloid and tau protein circulating in the bloodstream, which are these two markers of Alzheimer's disease.

Matt Walker (19:28):

Why is that relevant to the glymphatic system? It's relevant because two of the pieces of metabolic detritus that the cleansing system washes away at night, β-amyloid and tau. I'm sure enough of what they found was that not only did the adults sleep longer with these sleeping medications, they also had a greater clearance of β-amyloid and tau within the bloodstream. So this was the exact opposite of the Ambien study, which was where they were seeing an impairment in the glymphatic activity. Here in humans was a study with the web 3.0 sleep medications. Suvorexant, not only did it increase sleep, but it seemed to increase. Well, the assumption was that it was increasing glymphatic clearance because at least as the end outcome product, there was greater clearance of β-amyloid and tau protein in the blood. It wasn't just junk sleep, it was functional sleep. So for the first time I'd seen a sleeping medication that increased sleep more naturalistically, but that increased sleep made you the organism function better the next day as a consequence. Does that make any sense?

Eric Topol (20:38):

Absolutely. And it's interesting that we may have a sleep medicine finally or a class that actually is doing what is desired. This is one of the other things I was going to ask you about is that as you pointed out, this is an interaction throughout the organism, throughout the human being, and we've seen studies about how sleep disrupts metabolism and through that of course, and even separately, can take down our immune system or disrupt that as well. And so, one of the questions I guess is your thoughts about these other effects because you mentioned of course the potential of looking at things like p-Tau217 markers or other markers that would denote the status of your ultimate risk for moving on to Alzheimer's disease. But there's these other factors that also play a role with lack of adequate sleep and perhaps particularly sleep quality. I wonder if you could just comment about this because there's so many different systems of the body that are integrated here, and so the sanitary effect that you just described with the ability to potentially see less, at least biomarkers for what would be considered risks to ultimately develop Alzheimer's, there's also these other very important effects when we talk about high quality sleep, I guess, right? And maybe you could comment about that.

Matt Walker (22:21):

Yeah, I think quantity is what we've been talking about in some ways, but quality has also come onto the radar as absolutely essential. And what we find is that the quality of your sleep is as if not more predictive of both all-cause mortality, cardiovascular mortality, metabolic mortality, and in some regards, cancer mortality as well. And when I say quality of sleep, what we're really referring to here is at least one of two things. One is the continuity of your sleep. So you could be sleeping for eight and a half hours according to your sleep tracker, but maybe you are getting eight and a half hours by spending ten hours of time in bed because you are awake so much throughout the night and your sleep is very sort of punctured and littered with all of these awakenings across the night. That's sufficient quantity of sleep eight and a half hours, but it's poor quality of sleep because you are spending too much time awake.

Matt Walker (23:30):

And so, our measure of quality of sleep typically is what we call sleep efficiency. Of the time that you are in bed, what percent of that time are you asleep? And we like to see some measure of at least 85% or above because once you get less than 85% in terms of your sleep quality or your sleep efficiency, then you start to see many of these unfolding system-wide impairments. You seem to have high risk of diabetes, high risk obesity, high risk, as we said, cardiovascular disease. Also, hormonal changes both in men and in women. We see upstairs in the brain with poor quality of sleep, much more so than quantity of sleep. Poor quality of sleep is a more powerful predictor of mood disturbances and psychiatric conditions. And in fact, I think if you look at the data, at least in my center in the past 23 years, we've not been able to discover a single psychiatric condition in which sleep is normal, which to me is a stunning revelation. And what that tells us is that in many of those conditions they do seem to be getting not too bad of quantity of sleep. What is the marker of psychiatric sleep disturbance is not short quantity, it's poor quality of sleep. So I think it's a wonderful important point that I don't think we pay enough attention to, which is the quality.

Eric Topol (25:05):

Yes. And the other thing that you've emphasized, and I just want to reiterate to people listening or watching that is the regularity story, just like you said with quality. The data and I'll put the figure in that shows the link between regularity and cardiovascular, neurodegenerative, cancer, that regularity thing. A lot of people don't understand how important that is as well.

Matt Walker (25:30):

Stunning study from data from the UK Biobank, and this is across thousands and thousands of individuals and they tracked quantity and they tracked regularity and they split people up into the quartiles, those who were most regular and those who were least regular. And as you'll see in those sort of the figure that you flash up, those people who were in the upper quartile of regularity, de-risk all-cause mortality, cancer mortality, cardiovascular mortality, it was stunning. And then they did a cute little experiment of a statistical test where they took quantity because they had it in these individuals and regularity and they kind of put them in the same statistical bucket and did a sort of a Coke Pepsi challenge to see which one won out. And what it seemed to be was that regularity almost beat out quantity in terms of predicting all-cause mortality. Now that's not to say that you can get away with saying, well, I sleep four hours a night, but I sleep very regularly, consistently four hours a night. No, you need both, but regularity. I was someone who based on my remarkably vanilla and pedestrian personality, I've always been quite regular in my regard. But goodness me, even when I read that paper, I thought I'm doubling down on regularity. It's so important. That tells us, I think something that is in some ways a story not about sleep. It's a story about your circadian rhythm.

Matt Walker (27:02):

We speak a lot, or I speak a lot about sleep, and I think I've probably done a mis service to the other aspect of the sleep wake rhythmicity, which is called your 24 hours circadian rhythm. Now your sleep pressure, the drive to sleep is independent of your circadian rhythm, but they often work beautifully in harmony with each other, and you fall asleep, and you stay asleep. But I think the circadian system is critical because, excuse me, and what the circadian rhythm also regulates, sneezing right at the inopportune moment when you are recording a podcast. But nevertheless, what that tells me is that when you feed your brain signals of wake sleep consistency, which is to say wake, sleep, timing, regularity, there is something about feeding the brain signals of regularity that anchor your 24-hour circadian rhythm and as a consequence, it improves the quantity and the quality of your sleep. They're intertwined.

What About Sleep Trackers?

Eric Topol (28:09):

That's a terrific explanation for what I think a lot of people don't appreciate it's importance. Now, last topic about tracking. Now we understand how important sleep is. It is the superpower I am with you on that really brought that to light in so many ways. But of course, now we can track it with rings with smart watches and we get these readouts things like efficiency as part of the Oura score and other rings and deep sleep or NREM, REM, the works, you can see your awake times that you didn't know you're awake and the whole bit. Do you recommend for people that aren't getting great sleep quality beyond that they should try to establish a regular schedule that they should track to try to improve it and of course how would they improve it? Or are these things like having a cold mattress temperature that is controlled? What are the tricks that you would suggest for trying to improve your sleep through tracking? Or do you think tracking shouldn't be done?

Matt Walker (29:16):

Oh gosh, it's such a wonderful question and as with wonderful questions, the answer is usually it's complicated and I have to be careful because for someone who's currently wearing three different sleep trackers, it's going to be hard for me to answer this question completely in the negative. And there are three different sleep trackers. But I would say that for the most part, I like the idea of sleep tracking if you are sleeping well, meaning if as long as you're not suffering from insomnia. The reason is because sleep unlike those two other critical of health, which is diet and exercise, is very difficult to subjectively estimate. So if I were to ask you, Eric, how many times have you worked out in the past week, you'd be able to tell me how cleanly or how poorly have you been eating in the past week. You could tell me.

Matt Walker (30:09):

But if I was to say to you, Eric, how much deep sleep did you get last Tuesday? And if you don't have a sleep tracker, you'd say, I don't know. And so, there's something useful about tracking, especially a non-conscious process that I think is meaningful to many. And often medicine we say what gets measured gets managed, and there is that trite sort of statement. I do think that that's still true for sleep. So many people I've spoken to have, for example, markedly reduced the amount of alcohol consumption because they've been seeing the huge impact that the alcohol consumption in the evening has on their ring smart ring data as a consequence. So overall, I think they're pretty good. When people ask me what's the best sleep tracker, I usually say it's the one that you wear most frequently because if I come up with a band, headband, chest straps, all sorts of different things and it's a hundred percent accurate, but after three uses of it, you stop using it, that's a useless sleep tracker. So I like to think about sleep trackers that are low friction and no friction. When we go to sleep, we take things off, we don't put things on. That's why I liked things like the ring. For example, I think that's a non-intrusive way. I think the mattress may be as if not better because it's a completely friction less device. You don't have to remember to charge it. You don't have to put it on, you just fall into bed, and it tracks your sleep.

Matt Walker (31:40):

One form factor, I like to think about sleep trackers is the form factor itself. But then the other is accuracy. And I think right now if you look at the data, probably Oura is winning the ring kind of wars. If you look at all wristband wars, I think it's probably the most accurate relative to something like Fitbit or Apple Watch or the Whoop Band. But they're all pretty close. I think Oura is probably the leader in class right now at least. Keep in mind that I used to be an advisor for Oura. I want to make that very clear. So take what I say with a grain of salt in that regard. I think to your question, well, I'll come back to mattresses in just one second.

Matt Walker (32:34):

For people who are struggling with sleep, I think you've got to be very, very careful with sleep trackers because they can have the counterproductive effect where I gave you the example of alcohol or eating too late. And these sleep trackers help you modify your behaviors to improve your sleep. Well, there are places where these trackers can actually do you a disservice. When you get so hyper focused on your data and your data not looking good each and every day, it becomes a self-fulfilling prophecy of a negative spiral. And we now have a condition in sleep medicine called orthosomnia. So ortho in medicine typically means straightened. So you've heard of orthodontic straightening teeth, orthopedic straightening bones, orthosomnia is about getting so obsessed with getting your sleep perfect and your sleep straight that it causes an insomnia like syndrome. Now, I don't know, I think the press has made more of this than there is.

Matt Walker (33:30):

It probably is about 5-7% of the population. I would say at that moment in time, do one of two things. Either take the ring off entirely and just say, I'm going to get my sea legs back underneath me, get some cognitive behavioral therapy for insomnia. And when I'm confident I'll put the ring back on. Or don't throw the baby out with the bath water, keep wearing the ring. Try to say to yourself only on let's say a Sunday afternoon, will I open up the app and look historically what's been happening during the past week so that you keep getting your data, but you don't get the angiogenic daily sort of repetition of reinforcement of I'm not sleeping well. I should also note by the way that I think sleep trackers are not a substitute for either a sleep recording laboratory, but also, they're not a substitute for ultimately telling you entirely how good your sleep is.

Matt Walker (34:24):

Don't forget, you should always keep in mind how do I feel the next day? Because I think a lot of people will see their readiness score as 92 and they feel miserable. They just feel rough. And then another day, my readiness score was 62 and I just went out and I just ran my fastest five mile that I've done in the past six months. So don't forget that subjective sense of sleep is just as important as objective measures of sleep. The final thing I would say to your point about the mattresses, I actually do think that they are a really great vehicle for sleep augmentation because these smart mattresses, they're filled with sensors, things like Eight Sleep, and they will assess your physiology, they will track your sleep just like a sleep tracking ring. But what's also good is that because they can manipulate temperature and your sleep is so thermoregulatory sensitive that they create this kind, it's almost like this bent arc of thermal story throughout the night because you have to warm up at the surface to cool down at the core to fall asleep, then you have to stay cool to stay asleep, then you have to warm up to wake up and they take you through that natural change.

Matt Walker (35:41):

But they do it intelligently because they're measuring your sleep minute to minute. And then they're saying, I'm tweaking temperature a little bit. Has sleep improved? Has it become worse? Oh, it's become better. Let's lean into that. Let's get them even colder. Oh, wait a second, it's getting worse. Let's warm it back up a little bit. It's like a staircase method, like a Richter shock. And gradually they find your sweet spot and I think that is a really elegant system. And now they're measuring snoring. Snoring perturbations, and they can augment the bed and raise the angle of the bed up just a little bit so that the gravity doesn't have as much of a hold on your airway because when you're lying on your back, the airway wants to collapse down to gravity, and when you raise back up again, it will change that. And so, I think that there's lots of new advantages in, I think mattress technology that we'll see coming out into the future. I think it's a great vehicle for sleep augmentation.

Eric Topol (36:37):

That's terrific. Well, this has been for me, very educational, as I would've predicted, if anybody's up on everything in this area, it would be you. So thank you, Matt. It's a really brilliant discussion, really enlightening. We could talk some more hours, but I think we've encapsulated some of the big things. And before we finish up, is there anything else you wanted to say?

Matt Walker (37:05):

No, I think just to thank you for both your work in general in terms of science communication, your offer here specifically to allow me to try to be a very poorly communicated voice of sleep, and also just what you've done in general for I think the accuracy of science communication out into the public. Please never stop, continue to be a shining light for all of us. You are remarkable. Thank you, Eric.

Eric Topol (37:31):

Oh, you're very kind. And I look forward to the next chance we get to visit in person. It's been too long, Matt. And all the best to you. Thanks for joining today.

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