This is Your Brain on Sleep

Summary

---

Curiosity Weekly: "This is Your Brain on Sleep"

Host: Dr. Samantha Yammine
Guest: Dr. Jeffrey Iliff, Professor of Psychiatry, Behavioral Sciences & Neurology, University of Washington
Date: November 26, 2025

---

Episode Overview

This episode explores the fascinating, multifaceted science of sleep: why we need it, how it shapes our brains and bodies, and the remarkable processes at play during the nightly cycle. Dr. Samantha Yammine interviews Dr. Jeffrey Iliff, co-discoverer of the brain's glymphatic system, to delve into the “brain-cleaning” function of sleep, the molecular drivers of sleep across species, connections to brain health and disorders like Alzheimer’s, and insights from cutting-edge research on sleep diversity. The show also unpacks a new study proposing five different sleep types, their brain patterns, and their connections to mental health.

---

Key Discussion Points & Insights

1. The Science and Evolution of Sleep ([02:10]–[06:37])

• Sleep is universal among humans, but far from fully understood—research has long debated its evolutionary functions: memory consolidation, metabolism, immune function, brain “pruning,” and detoxification.
• Animals show extraordinary diversity in sleep:
  • Jellyfish don’t sleep in the human sense, but display rhythms akin to rest ([03:22]).
  • Dolphins sleep one brain hemisphere at a time—“Talk about multitasking!” (Dr. Yammine, [02:45]).
  • Placozoans (simplistic, brainless animals) slow down at night, suggesting even the simplest creatures have circadian cycles ([04:24]).
• Groundbreaking research links sleep drive to mitochondria—cellular powerhouses—via electron “leakage”:
  • “When [researchers] reduced the electron leakage, the flies slept less, and when they increased it, they slept more.” (Dr. Yammine, [05:37])
  • Implies sleep’s deepest roots may be metabolic, with other benefits piggybacking.

2. What’s Happening in Your Brain during Sleep? ([09:31])

• Our brains shift through “three or four really different identifiable electrophysiological states” during sleep (Dr. Iliff, [10:27]).
• REM (dream) sleep is best known, but “slow wave sleep” is the deepest phase, marked by synchronized neuronal activity/inactivity oscillations ([10:56]).
• “It seems like [the] brain is doing very, very different things through the course of the night…biologically, what’s happening…we’re only just starting to get a sense of.” (Dr. Iliff, [11:18])

3. The Glymphatic System—Your Brain's Nightly Cleanse ([11:32]–[13:28])

• Dr. Iliff’s research identified the glymphatic system: a fluid-based process by which the brain removes metabolic waste.
  • During sleep—specifically, slow wave sleep—your brain enters “cleaning mode,” flushing out waste accumulated during the day ([12:29]).
  • “[Sleep] allows the clearance of wastes that accumulate in the brain through the course of the waking day.” (Dr. Iliff, [12:53])
• Glymphatic vs. Lymphatic systems:
  • The lymphatic system (body-wide) clears waste and supports immunity, but the brain has no lymphatic vessels. Instead, glial cells support the “glymphatic” cleaning process within the brain. (Dr. Iliff, [13:28])
  • Later research showed lymphatic vessels do exist around (but not in) the brain and assist in fluid clearance ([14:10]).

4. Waste Clearance, Sleep “Quality,” and Brain Function ([14:46])

• Lack of sleep impairs brain “pruning” (synaptic downscaling) and may limit glymphatic waste removal, potentially causing post-bad-night grogginess and cognitive dysfunction.
  • “How much…actually contributes to how you feel after you don’t sleep and how you’re thinking after you don’t sleep? We actually don’t know the answer to that yet.” (Dr. Iliff, [15:52])
• Possible link between migraines and glymphatic dysfunction has been found in animals, not yet in humans ([16:39]).

5. How Glymphatic Research Is Conducted ([16:57])

• In animals: Tracers (fluorescent or MRI) are injected, then tracked through brain tissue.
• In humans: Usually MRI-based, since invasive tracers aren’t practical. Researchers track water movement in the brain and measure amyloid/tau protein clearance via blood samples ([17:10]).
• Fluctuations in blood levels of these proteins may indicate the brain’s overnight “cleaning” cycles ([19:33]).

6. Sleep, Dementia, and Alzheimer’s ([20:02])

• Poor sleep is a “clear risk factor” for dementia—including Alzheimer’s—based on large-scale epidemiology ([20:21]). Notably:
  • Both too little (<6h) and too much (>9h) sleep elevate dementia risk (“U-shaped” curve).
  • Quality matters as much as quantity—fragmented, “crappy” sleep increases risk ([21:08]).
  • Midlife sleep (age 40s-50s) is most predictive for later dementia risk ([21:34]).
  • “It goes both ways”—as people develop dementia, their sleep also worsens.

7. How Do You Measure “Good” Sleep? ([22:01])

• Despite new data (from wearables, etc.), we still don’t precisely know what constitutes “good” or “sufficient” sleep—subjective satisfaction often doesn’t align with objective sleep stage data.
  • Aging reduces slow wave/deep sleep, but many elderly people don’t feel impaired ([22:11]–[23:57]).
  • 30 years ago, the only available measure was “Do you sleep well?”—now we have copious quantitative data, but it’ll be decades before we know how it correlates to health outcomes ([23:57]).

8. Are Sleep Trackers Useful? ([24:22])

• Sleep tracking wearables (Garmin, Apple Watch, etc.) are around 70–85% accurate compared to gold standard studies. Useful for individual feedback, but not perfect ([24:57]).
• “[Within] an individual, I think it can be very useful for understanding what are the factors that affect your sleep...when you sample it every day you...get a sense of cause and effect.” (Dr. Iliff, [26:39])

9. Do Some People Truly Need Less Sleep? ([27:13])

• There is both behavioral and genetic variability in sleep need—some people function on minimal sleep, but may not realize they could be even more functional with more rest ([27:20]).
  • “There does seem to be a genetic determinant of how much sleep you need and how quickly you can dissipate sleep need.” (Dr. Iliff, [27:57])
• It’s unknown whether “short sleepers” are protected from dementia risk ([28:17]).

10. Weekend “Catch Up” Sleep and Social Jet Lag ([28:41])

• Your body prefers regularity; erratic schedules or “recovery sleep” on weekends causes “social jet lag”—akin to a weekly transatlantic flight.
  • “Essentially it’s like you’re taking a transatlantic flight every weekend…you’re just kind of always jet lagged.” (Dr. Iliff, [29:53])

11. Practical Advice & Misconceptions ([31:01])

• Sleep hygiene advice is widely published (“Don’t drink caffeine after 3pm…quiet, cool room…don’t work in your bedroom…”).
• Two lesser-discussed tips:
  1. Try eight hours for two weeks as an experiment. Dr. Iliff did, and “it was crazy…like I was a totally different human than I thought I could be.” ([32:13])
  2. Think about the long view: “Your sleep habits in your 40s and 50s...is going to determine what your brain is like when you’re in your 60s and 70s and 80s.” ([33:06])

---

Notable Quotes & Memorable Moments

• "Most animals sleep, but not all of them. And we’re not exactly sure why."
  — Dr. Samantha Yammine ([02:34])

• "The brain is actually shifting into a kind of cleaning mode where that flushing of fluid...is actually turning on during sleep."
  — Dr. Jeffrey Iliff ([12:34])

• "You could imagine getting eight hours of sleep, but maybe it’s of a different quality than another person who gets eight hours."
  — Dr. Jeffrey Iliff ([23:29])

• "[Wearables] are right within me, right? So if I have a terrible night of sleep...my watch knows…my watch tells me."
  — Dr. Jeffrey Iliff ([25:39])

• “Try the experiment…set a going to bed alarm and a waking up alarm so that you would get eight hours of sleep…just do it for two weeks and see if that doesn’t unlock more function than you thought you had.”
  — Dr. Jeffrey Iliff ([32:12])

• “Your sleep habits in your 40s and 50s…is going to determine what your brain is like when you’re in your 60s and 70s and 80s.”
  — Dr. Jeffrey Iliff ([33:06])

---

Highlighted Segment Timestamps

• [02:10] – Introduction to animal sleep variation and the evolutionary context
• [09:31] – Why sleep matters biologically and cognitively
• [10:27] – Brain’s electrophysiological stages during sleep (REM, slow wave, etc.)
• [11:45] – The glymphatic system: discovery and function
• [13:28] – The confusing terminology: glymphatic vs. lymphatic systems
• [15:58] – Can poor glymphatic function explain morning headaches?
• [17:10] – How researchers study glymphatic activity in animals & humans
• [20:21] – Sleep as a dementia and Alzheimer’s risk factor
• [22:11] – What actually defines “good” or “enough” sleep?
• [24:57] – The practical usefulness of sleep-tracking tech
• [27:20] – Do we really need as much sleep as we think?
• [28:54] – The pitfalls of sleeping in on weekends (“social jet lag”)
• [31:16]–[33:27] – Dr. Iliff’s practical takeaways and personal experience

---

New Research: The Five Types of Sleep ([36:40])

• Concordia University study identified five sleep patterns among young adults:
  1. Low satisfaction/psychological distress — Trouble falling/staying asleep, lower cognitive performance, mental health symptoms.
  2. Sleep resilient — Okay sleep despite psychological symptoms.
  3. Frequent sleep aid users — Few sleep complaints but lower visual memory.
  4. Short sleepers (<6–7h) — Lower accuracy, increased aggression, higher brain network connectivity.
  5. Fragmented sleepers — High levels of anxiety, substance misuse, worse cognitive scores.
• “There are a lot of ways that sleep affects our bodies, our brains, and our mental health, and…we need to be looking at it from all angles.” (Dr. Yammine, [39:53])

---

Conclusion

This episode demystifies sleep as a complex, essential biological process, not just a passive shutdown. The conversation ranges from ancient cellular functions to modern biometrics, the “garbage collection” role of the glymphatic system, implications for brain health and disease, and the marvelously diverse animal world. Dr. Iliff’s firsthand advice is clear: try prioritizing eight hours for yourself, observe your own patterns with curiosity, and remember that what you do tonight may shape your brain decades from now.

---

Transcript

[Monday Sidekick / Sleep Number / California Lottery Announcer]

Monday Sidekick the AI agent that knows you and your business, thinks ahead and takes action. Ask at anything seriously.

[Workday Go / Earnin / Monday Sidekick Announcer]

Monday Sidekick AI you'll love to use.

[Monday Sidekick / Sleep Number / California Lottery Announcer]

Start a free trial today on Monday.com.

[Sundaes for Dogs / Lemonade Pet Insurance Announcer]

The holidays are about family and quality time, right? But while we're carving roast beef, our dogs are stuck with dry kibble mystery meat. And yes, they notice it's time to make the switch to sundaes. Sundaes is clean, whole food based food made for the dogs we love. It's air dried and made in a human grade kitchen using the same ingredients and care you'd use to cook for yourself and your family. Every bite of sundaes is clean and made from real meat, fruits and veggies with no kibble, no weird ingredients and no fillers. Because your dog deserves food made with care, not in the interest of cost cutting. And the best part? You just scoop and serve. No freezer, no thawing or prep. No mess. Just nutrient rich clean food that fuels their happiest, healthiest days so you get more of them to share together. Sunday's holiday sale is going on right now. Go to sundaysfordogs.com acast50 and get 50% off your first order. Or you can use code acast50 at checkout. That's 50% off your first order at sundaysfordogs.com accast50 don't miss out on Sunday's best sale of the year at sundaysfordogs.com Acast50 or use code Acast50 at checkout time.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

It's always vanishing. The commute, the errands, the work functions, the meetings, selling your car. Unless you sell your car with Carvana, get a real offer in minutes. Get it picked up from your door. Get paid on the spot so fast you'll wonder what the catch is. There isn't one. We just respect you and your time. Oh, you're still here. Move along now. Enjoy your day. Sell your car today. Carvana PICK up FEES MAY apply.

[Sundaes for Dogs / Lemonade Pet Insurance Announcer]

Sleep.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

You know it, you love it. And most of us do it every night. But for something that every person on the planet experiences, the scientific study of sleep is surprisingly complex. There are a lot of theories out there about why we need sleep and what the evolutionary functions of sleep have been throughout the history of our species. Some research says that we need sleep in order to process our memories. Others suggest it's an opportunity for our bodies to metabolize or for our brains to prune or even clear out waste after a long day. No matter the theory, we can all agree that sleep is One of the most important things that our bodies do. So for this episode of Curiosity Weekly, we'll be diving into the science of sleep. I'll speak with Dr. Jeffrey Eiliff, who is part of the research team that discovered the glymphatic system, which is all about how our brain cleanses itself through sleep. I'll also dig into a new study that proposes five different sleep types and how they affect our mental and bodily processes. Plus, we'll explore how we can learn more about human sleep patterns from studying the fun and different ways that animals sleep. My name is Dr. Samantha Youmeen. Let's dive in. Did you know jellyfish don't sleep well? Not in the same way that you and I do. Or how about dolphins? They only rest half their brains at a time. Talk about multitasking. Most animals sleep, but not all of them. And we're not exactly sure why. From the tiniest fruit fly to the majestic tiger or the stealthy bat to the drifting jellyfish, not all animals sleep the same. Some aren't thought to sleep at all. At least not in the way we typically think of sleep. Understanding the diverse ways animals sleep could unlock new treatments for sleep disorders, sleep medication, and help us all get some shut eye. Previous research looked at the big picture, the cost and benefits of how animals sleep. And then they honed in on two different factors that led to these behaviors. The threat of predation and the promise of food. When it comes to predation, for example, animals will sleep longer if they're in a protected place, like a burrow or treetop with food. Grazers like sheep or cows tend to sleep less because they need to spend a lot of their time eating. More recently, researchers have been looking into the molecular and cellular definitions of sleep to explore how it affects animal biology. And one of the best ways to explore sleep from that perspective is to study animals that don't have brains. For example, the jellyfish. They have a nervous system, but not a Central Brain. In 2017, a Caltech research team found that jellyfish showed evidence of both sleep and sleep loss if they were kept up too late. Another team studied one of the most simple creatures on earth, called placozoa. They're round, flat, transparent organisms, smaller than a sesame seed with just two layers of cells, none of which are nerve cells. They use hair like structures to propel themselves along until they find microalgae to graze on. But the team found that they slow this cruising down at night, suggesting placozoans have a circadian rhythm where they graze less at night, bringing the concept of sleep to organisms without a real nervous system. A study published in 2025 from a team at Oxford was the first to propose the link between sleep and mitochondria, the powerhouse of the cell. If you'll recall. Now, it's called that because mitochondria move electrons along inside them to help the cell generate energy. Looking at fruit flies, they found that some of those electrons leak off their path in the mitochondria, and that seemed to dictate how much the flies slept. When they reduced the electron leakage, the flies slept less, and when they increased it, they slept more. Now, this hasn't been tested in a mammal's brain, but it's the latest theory as to why most creatures, both big and small, need to doze every now and again. The researchers suggest that for animals, potentially including humans, sleep drive is triggered by that excess of leaked electrons, and sleep gives cells a chance to clear the metabolic backlog that builds up while we're awake. They even argue that the other benefits of sleep, like memory consolidation and immune regulation, are simply piggybacking. But the mitochondria call the shots. So whether it's a dolphin sleeping with only half its brain or placozoas snoozing before munching on some microalgae, sleep patterns can be traced down to the most microscopic functions in the body. This holiday Verizon is helping you bundle.

[Monday Sidekick / Sleep Number / California Lottery Announcer]

Up incredible gifts and savings.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

You'll get the latest phone with a new line on MyPlan and a brand new smartwatch and tablet. No trade in needed even on our lowest price plan. That's two gifts for your family and one for you. Or two for you and one for someone else. Or three gifts for you and only you. Either way, you save big on three amazing gifts at Verizon, all on the best 5G network. Visit Verizon today. Rankings based on RootMetric Truth Score Report.

[Sundaes for Dogs / Lemonade Pet Insurance Announcer]

Dated one each 2025.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

Your results may vary.

[Sundaes for Dogs / Lemonade Pet Insurance Announcer]

Service plan required for watch and tablet.

[Workday Go / Earnin / Monday Sidekick Announcer]

Additional terms apply New products to launch, new people to develop new goals to crush. Workday Go is designed for small and mid sized businesses. By bringing HR and finance together on one AI platform, you'll have everything you need to think big, go big and grow big. And activation is fast. It takes just 30 to 60 business days to get you up and running. Simplify your SMB on an AI platform, you'll never outgrow. Workday Go.

[Sundaes for Dogs / Lemonade Pet Insurance Announcer]

The holidays are about family and quality time, right? But while we're carving roast beef, our Dogs are stuck with dry kibble mystery meat and yes they notice it's time to make the switch to sundaes. Sundaes is clean whole food based food made for the dogs we love. It's air dried and made in a human grade kitchen using the same ingredients and care you'd use to cook for yourself and your family. Every bite of sundaes is clean and made from real meat, fruits and veggies with no kibble, no weird ingredients and no fillers because your dog deserves food made with care, not in the interest of cost cutting. And the best part? You just scoop and serve. No freezer, no thawing or prep, no mess, just nutrient rich clean food that fuels their happiest, healthiest days so you get more of them to share together. Sunday's holiday sale is going on right now. Go to Sundays for dogs.com Acast50 and get 50% off your first order. Or you can use code acast50 at checkout. That's 50% off your first order at Sundays for dogs.com Alast50 don't miss out on Sunday's best sale of the year@ Sundaysfordogs.com Acast50 or use code Acast50 at checkout. Got a new puppy or kitten? Congrats. But also yikes. Between crates, beds, toys, treats and those first few vet visits, you've probably already dropped a small fortune. Which is where Lemonade Pet Insurance comes in. It helps you cover vet costs so that you can focus on what's best for you and your new pet. The coverage is customizable, sign up is quick and easy, and your claims are handled in as little as three seconds. Lemonade offers a package specifically for puppies and kittens. Get a'llemonade.com pet your future self will thank you. Your pet won't. They don't know what insurance is.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

There's something about a good quality night's rest that nothing else can quite replace. We spend about a third of our lives doing it. Beyond helping us with our cognitive functions, you know, not being groggy all day, a growing body of evidence suggests sleep plays a role in our long term health too. We have to ask our favorite question on the show. Why? If the importance of sleep were just about resting, then relaxing on the couch should be enough. But it isn't. Decades of research working to answer this question has found sleep to be a much more active process than we might think, involving parts of the brain that were discovered by our guest. We're chatting with Dr. Jeffrey Eiliff, professor in the departments of psychiatry and behavioral sciences and in neurology at the University of Washington School of medicine. Welcome to the show, Jeff. We know our brains go through different stages of activity as we sleep and descend into deeper layers of unconsciousness. And I think rem, or the dream phase, is probably the most well known. But what else is happening in the brain while we sleep?

[Monday Sidekick / Sleep Number / California Lottery Announcer]

Quite a few different things, and some of them we may not really understand fully. So if. If you record electrical activity out of your brain while you're sleeping, one of the things that you immediately see is there are three or four really different identifiable electrophysiological states that your brain's in. So it isn't just, you know, asleep and awake, but it's rather your. Your brain is passing into and out of several different stages. One of them, as you mentioned, is rem, which is the one that we associate with dreaming. But then there's another. There's another phase called slow wave sleep, which you think of as being the deepest phase of sleep, where your brain is oscillating between times of intense synchronized activity and then intense synchronized inactivity. And it's oscillating between those about every second. Right. And those are. Those are the slow waves that people talk about. And so it seems like their brain is doing very, very different things through the course of the night. But in terms of biologically, what's happening while those different states are happening, we're only really just starting to get a sense of that.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

Can you tell me more about something else that you played a role in discovering happening during sleep, which is the glymphatic system and what it may be doing during those phases of electrical shifts, too?

[Monday Sidekick / Sleep Number / California Lottery Announcer]

Sure. So one of the things that we. We first observed, we were a research group, a neuroscience group, that was interested in what the fluid around the brain was doing. We did some studies initially in rodents. More recently, similar studies have been done in humans, where we injected a tracer into the fluid that surrounds the brain, the cerebral spinal fluid. What we observed was that that fluid didn't just sit around the brain as we had thought that it would, but rather it moved into and through brain tissue really rapidly. One of the things that it was doing was clearing away the wastes that in between the brain cells. Pretty soon after that, though, we asked the question of is this something that's happening throughout the day, throughout the night, all the time, or is this something that's physiologically regulated? One of the things that we observed, and this was published back in 2013, was that during sleep the brain is actually shifting into a kind of cleaning mode where that flushing of fluid from outside the brain through the brain tissue is actually turning on during sleep and during slow wave sleep in, so that one of the biological functions of sleep seems to be allowing the clearance of wastes that accumulate in the brain through the course of the waking day.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

Now you're talking about the glymphatic system with a G. But I know some people may be familiar with the lymphatic system throughout the body, and it's especially, I think, grown in conversation as gua sha techniques. For example, lymphatic drainage have become really popular, at least becoming more mainstream. They've been around for a long time, but it's been more mainstream recently. So can you tell us the difference between the lymphatic system and the glymphatic system in the brain?

[Monday Sidekick / Sleep Number / California Lottery Announcer]

Yeah, so it's actually double confusing. So when we first described the glymphatic system, the idea was that the brain, it doesn't have lymphatic vessels. So in the rest of your body, lymphatic vessels support a couple of things. One of that is clearance of fluid and proteins out of the spaces between your cells. And the other is immune surveill. And the brain, since it lacks lymphatic vessels, it must undergo those processes of waste clearance and immune surveillance some other way. And so we described this process of brainwashing or brain clearance. And we said, oh, this is a lymphatic process that's supported by your brain's support cells, which are called glial cells. So the glial, lymphatic or glymphatic system. The only trouble was, two or three years later, other researchers described lymphatic vessels around the brain. So they're not in the brain, but they're around the brain and they help to clear the brain. And so we have a glymphatic system which supports the clearance of stuff out of the brain into the fluid around it. And then we have lymphatic vessels that supports the clearance of stuff from that fluid out to the blood. So, you know, maybe if we knew that what was going to happen in the future, we would have chosen a less confusing thing.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

So if someone has a bad night's sleep, for example, how much of it is a lack of this waste removal or this brainwashing that you're describing? Like, is the glymphatic system playing a role or the lymphatic system in how good a night's rest we feel that we had.

[Monday Sidekick / Sleep Number / California Lottery Announcer]

So the answer to that question lives sort of in the space between what we know and what we think. Right. So at this point, we know that the brain is doing a lot of different things while you're. While you are sleeping. One of the things that it's doing is it's pruning away and snipping away connections that it doesn't need, that it formed through the course of the day, a process called synaptic pruning or synaptic downscaling that undoubtedly has a role to play in the cognitive dysfunction that you have when you don't sleep. We think that an impairment of brain waste clearance also is contributing to that cognitive impairment that you see after poor sleep. But how much one of those processes or the other process or some other other process yet actually contributes to how you feel after you don't sleep and how you're thinking after you don't sleep? We actually don't know the answer to that yet.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

Yeah. I think I've heard some people say, like, that headache from a lack of sleep could be due to this improper drainage, But I never actually fact checked if that was true or that's just like a speculation.

[Monday Sidekick / Sleep Number / California Lottery Announcer]

Yeah. In your head, you can think through how all sorts of things might be attributable to that phenomenon. Right. And it's part of being a scientist is being a storyteller. You see events and you try to create stories of how those events and how those observations are connected. And it's really easy to connect. Oh, if you're not sleeping well, maybe the inflammatory molecules around your brain aren't being cleared up well enough. And so the pain fibers that are around your brain, in the membranes around your brain, they're becoming sensitized and inflamed, and that's why you're having a headache. That makes sense. There's actually some data that came out probably about two years ago suggesting that migraines indeed are connected to glymphatic function. But that's so far only been demonstrated in animals, not in humans. Yet.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

And then how are you studying glymphatic system during sleep? Because it's the movement of liquid. So is it all through tracing molecules or tracing chemicals? And you have people in an imaging device. What does that research look like?

[Monday Sidekick / Sleep Number / California Lottery Announcer]

So the answer to that question changes dramatically whether you're talking about studying it in an animal or studying it in a human. In animals, most often, what we're doing is we're doing imaging into the brain of living animals. After we inject a Tracer of some sort, whether that's a fluorescent colored molecule that we can see under a microscope, or whether that's an MRI contrast agent that we can see in an MRI magnet. That's how we study that in animals. In humans, we're much less likely to inject something into the fluid that surrounds your brain. That's just not a thing that people take trivially. And so most often what people are doing is using MRI based approaches. So in mri, what you may not know about it, when you think about it, you think, oh, it's taking a picture of inside my body. But in mri, what it's actually detecting is the properties of water. So water is the thing that the protons of water that MRI is detecting differences in. MRI actually ends up being a really valuable tool for understanding how water is moving around the brain. And the movement of water around the brain has a lot to do with how solutes and wastes are cleared out of the brain during sleep. There are people though, that are. The trick with that is if you ever want to, like, if you wanted to go get your brain clearance measured, you could go to a research university like ours in Seattle, or you could go to another big one in Boston, or, you know, in San Diego. But if you live in a normal place and not one of those places, that's not going to work. And so there's actually companies out there now and groups that are trying to devise non MRI approaches to measuring clinical lymphatic function, whether that's with a blood test or whether that's with a device that measures it or something else. So in the Alzheimer's field, one of the things that's commonly done now is you can draw blood and you can measure how much amyloid and tau is in the plasma and the different kinds of amyloid and tau that's in the blood. And that tells you something about how much amyloid plaque burden you have in your brain or how much tau pathology you have in your brain. And those are being used right now diagnostically for diagnosing do you have Alzheimer's disease or not? Right. So that's a new thing. But one of the things that we've observed is if I measured your blood six times a day for a week, one of the things that we would see is that your blood levels of amyloid actually go, they change throughout the day. And you might think that that's just noise in the measurement, that it's just, oh, it's an inexact measurement, but there's actually information in Those changes. And so we think that what you can do is you can actually pick up the clearance of amyloid and tau out of the brain to the blood by looking at overnight changes in amyloid and tau levels in your blood.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

I'm glad you brought up Alzheimer's because I know that's something your lab studies, looking at the connections between poor sleep, for example, and diseases like Alzheimer's and traumatic brain injury as well. How strong is the connection there between poor sleep sleep, Is it a risk factor for Alzheimer's or vice versa? What do we know so far?

[Monday Sidekick / Sleep Number / California Lottery Announcer]

It's clearly a risk factor. So if you look epidemiologically, so in very large groups of people in the population, what you see is that people who have poor sleep, and that's a pretty broad term, it's kind of a general term, they're at an increased risk of really dementia from any cause and Alzheimer's disease in particular. The data suggests that people who sleep too little, so people who sleep less than six hours a night, and people who sleep too much, people who are asleep for more than nine hours a night, both groups are at an increased risk of dementia. They call it a U shaped curve where risk increases at the low end and at the high end, people who sleep not just short or long, but also crappy, they are also at an increased risk of dementia, those data suggest, because it's actually midlife sleep. So it's the sleep that you're having in your 40s and 50s that is the thing that's determining your risk for dementia in your 70s and 80s that suggests that it's an upstream risk factor. But there's also data to suggest that people, as they move into and toward dementia, their sleep gets worse and worse and worse, right? So everyone, if you've ever had a loved one who is demented or had dementia, it's the sleep disruption that actually makes it almost impossible to care for them in the home. And that ends up being one of the reasons why people have to move from an in home care environment into an institutional care environment, is because the sleep gets so jacked up, right? And so it goes both ways, but it does seem to be a midlife risk factor.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

What does poor sleep or good sleep really mean, especially when it comes to our overall health or our risk for these types of things?

[Monday Sidekick / Sleep Number / California Lottery Announcer]

It's a little bit, it's a tricky thing because I actually don't think we have a really good handle on the answer to that question. So if you ask a person, one of the things that we observe Is that as people age, unless they're sick, they tend to sleep less and less and less as you get older. And if you talk to people, I don't know if you have a healthy grandparent or a healthy aunt and uncle, many times they'll just say they're like, I'm fine. I can function just fine on my seven hours or six hours or five hours of sleep. And so there's this feeling or this sense that they seem to think or feel as though they're sleeping fine. But if you measure their sleep as people get older, many of them don't have hardly any slow wave sleep at all. And so they're missing this whole electrophysiological state. Yet when you talk to them, they don't complain of a lot. These are even people without something like sleep apnea or insomnia. They're just old people who they get up a couple times during the night because they have to go to the bathroom or their back hurts. It's a little bit hard to understand. Is it how you feel about your sleep that matters? Is it quantitative? Do you need X number of hours? You could imagine getting eight hours of sleep, but maybe it's of a different quality than another person who gets eight hours of sleep. So is it the quality of sleep matters? And so the actual active ingredients in that risk? We don't have a good, I don't think that we have a good sense of. Thirty years ago, the questions that we were asking about sleep were like, do you sleep well? And that was it. Right. And so whereas now, you know, even, you know, consumers, I look at, you know, I have a Garmin watch on that tracks my sleep every single night. And I know exactly what goes in and what goes into a good night's sleep, and I know exactly what keeps me from sleeping well. And so we have all this data now. Now, but it's not going to be useful for predicting whether I'm going to get dementia for another 20 years. And so when we're trying to understand cause and effect, we have to look back at the data we were collecting 25 years ago, which in the case of sleep, wasn't very good.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

I'm intrigued that you wear one of these devices that gives you feedback on your sleep. I wanted to ask you because sleep optimization is a huge trend right now, as I'm sure you've seen. And a lot of people are looking at these qualitative reports like, yes, you had a good night's sleep today or you did not. Are these proxy biometrics One, are they ones that are helpful in this type of research or that you kind of agree with? Do we know, is there a way to do a wearable for the glymphatic system in some way? Where do you see that going as we learn more about sleep?

[Monday Sidekick / Sleep Number / California Lottery Announcer]

So there's the brass tacks question, which is, hey, my Apple watch says I had 1 hour and 35 minutes of deep sleep last night. Is that true? And I had 48 minutes of REM sleep. And the sort of bedrock validity of the wearables that we're using now against gold standard sleep study type stuff. So polysonography, it's pretty good, you know, it's like 70, 85%, right? Is that good enough to diagnose sleep apnea? Maybe? Is it good enough to, you know, is it good enough for a research study maybe? Is it good enough, you know, is it, is it 100%? No. And so there's, there's real, there's limitations there. It's getting better, certainly the algorithms for detection are getting better, but on the other hand, within person. So I've been wearing a Garmin watch and I'm not paid by Garmin. It's just happened. I run with my daughter, I run with my daughter and I run together and that's what we use. So it tracks my sleep. I find whether or not it's exactly right. It's right within me, right? So if I have a terrible night of sleep because I was up until 1am Working on a work thing and so then when I go to bed, my brain's all spinning and then I have to wake up at 6, my watch knows, knows that if I have two beers instead of one beer, I have less REM sleep. And my watch tells me so I know that when I'm jet lagged, I have crappy sleep. I know that when I run too close to when I go to bed, I have shallow sleep. And so for me individually, what it helps me see is what the input output function is for my sleep, sleep for what I do in my life and the sleep I get. And so within an individual, I think it can be very useful for understanding what are the factors that affect your sleep. And it's only when you sample it every day do you actually start to get a sense of cause and effect for you. And so that's really useful, I think.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

Is it true that some people need less sleep than others? Do we know if that's true or even why?

[Monday Sidekick / Sleep Number / California Lottery Announcer]

So it is definitely true that there are, are there? Well, behaviorally There are people that sleep less than other people. Some of that is by choice, right? So if you say you sleep, you know, six hours a night, and when a friend says, why don't you sleep more? You say, I'm great, I'm perfectly functional. That may be true. What you don't know is if you slept eight hours a night, whether you would be even more functional than you are now. So I think while many people say they can function on not a lot of sleep, a lot of times, that's what they don't know is that there is sort of another gear of function that is available to them if they optimize their sleep better. The flip side of that though, is there does seem to be a genetic determinant of how much sleep you need and how quickly you can dissipate sleep need. And that does seem to have an actual genetic component to it. What we don't know is whether people who have less need of sleep, quote, unquote, are at a reduced risk of Alzheimer's disease. So we don't have those data yet. There aren't enough of those people that hasn't been studied enough. So we don't really know if that sense of needing less sleep day to day translates to needing less sleep over the course of 30, 40, 70 years.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

Is it really important to get that good quality length of sleep every single night, or can you make up for it on the weekend if you sleep in more? Do we know how that impacts our health and our risk for things?

[Monday Sidekick / Sleep Number / California Lottery Announcer]

Things, yeah. So in general, your body. The body functions cyclically and homeostatically, which means it tries to keep itself within a narrow range of just sort of where it's at. Right? And as you might imagine, a machine that operates like that operates best when things are always the same. Right? So your circadian sleep drive, which is the part of your sleep drive that connects you to the 24 hour light dark cycle, and your homeostatic sleep drive, which is the part of you that connects to how long have I been awake and how tired I am versus how tired I am. Those two things align best when you go to bed and wake up at the same time every single day, like forever, Right? That's the optimal situation. Of course, that's none of our life. And so then the question is, if during the week your life only allows you to sleep six hours a night, what should you do on the weekend? Should you just go with that or should you try to recover something? There is a phenomenon called recovery sleep, which is where, when you restrict sleep for a while or when you restrict sleep, you build what's called sleep debts or sleep. There's like this need for sleep that you haven't been fulfilling. And when you finally do sort of have unrestricted sleep, you'll sleep longer. And that's your body trying to claw back some of what it's missing. But one of the tricks with that is if you do that, and this is the thing that teenagers and young people do, right, Is you know, you're sleeping five hours a night and then on the weekend you sleep for like 14 hours. Essentially it's like you're taking a transatlantic flight every weekend. And so you're undergoing what's, it's called social jet lag. Right. So you spend your weekend jet lagged from your week, your during the week shifting from your during the week schedule and then you spend the beginning of the week shifting, shifting back from your weekend schedule and you're just kind of always jet lagged.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

This has all been so fascinating. I wanted to wrap by asking, you know, do you have, if you have advice for people when it comes to their sleep or if there's anything that you see that we kind of tend to get wrong about sleep that you'd really want to correct something we didn't touch on yet?

[Monday Sidekick / Sleep Number / California Lottery Announcer]

Yeah. So I think there's the obvious ones, right. So if you put into chatgpt or whatever you're doing, hey, what do I need to do to sleep better? It'll give you all the sleep hygiene things. And those are all, everyone knows those. It's don't drink caffeine after 3pm and it's go to sleep and wake up at the same time every day. Have a quiet cool room, right? Don't work in your bedroom, right. You should only be doing two things in your room. Like there's a, there's all of those things. Everyone's heard those, everyone knows them. You can look them up. I think two additional things we're thinking of. So when I first started doing this particular line of work, I wasn't actually a sleep researcher. I was just a researcher researcher. And in my field it's very demanding and there's a lot of pressure to produce. And the one compressible thing in my life with a family and with a career was sleep. And so I probably slept five or six hours a night night. And I was highly productive and I thought it was fine. And then I had a colleague, she was from ucla, she's a sleep psychologist. She said, do an experiment, set an alarm on your phone. For going to bed, a going to bed alarm and a waking up alarm so that you would get eight hours of sleep and just do it for two weeks. Don't do it for the rest of your life. Just do it for two weeks and see if that doesn't unlock more function than you thought you had. And I did it and it was crazy. It was like I was like a totally different human than I thought I could be. And so now I'm this crazy sleep person where I'm just like, oh, I have to be at bed at 9:30 because I'm going to get up at 5:30, which is really crazy when you're not that I don't feel like I'm that old. So try the experiment. The second thing is you think that the sleep that you're going to have that you have tonight and the sleep that you have tomorrow night is going to impact maybe your next couple days and maybe it's going to be a rough couple days. But I think what the data suggests suggests is your sleep habits in your 40s and 50s and I suspect we're going to learn that it's also true in your 20s and 30s but we just don't have those data yet. Is going to determine what your brain is like when you're in your 60s and 70s and 80s. And now that we're all going to be lived to be 120 years old, I think that's going to matter.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

Very well said. That's been Dr. Jeffrey Eiliff, professor at the University of Washington School of Medicine. Thank you so much for joining us on the show Jeff. That was fascinating.

[Monday Sidekick / Sleep Number / California Lottery Announcer]

Thanks Sam. My pleasure.

[Workday Go / Earnin / Monday Sidekick Announcer]

Think enterprise software is too costly, too complex and takes too long to get up and running. Think again. Workday Go makes simplifying your small or mid sized business simple HR and finance together on one powerful AI platform. Right? Right at your fingertips. Workday Go gets you live fast and fits the needs of your business. Find out what Workday Go can do for you. Go with Workday Go.

[Sundaes for Dogs / Lemonade Pet Insurance Announcer]

The holidays are about family and quality time, right? But while we're carving roast beef, our dogs are stuck with dry kibble mystery meat. And yes, they notice it's time to make the switch to sundaes. Sundaes is clean whole food based food made for the dogs we love. It's air dried and made in a huge human grade kitchen using the same ingredients and care you'd use to cook for yourself and your family. Every bite of sundaes is clean and made from real meat, fruits and veggies. With no kibble, no weird ingredients and no fillers because your dog deserves food made with care, not in the interest of cost cutting. And the best part? You just scoop and serve. No freezer, no thawing or prep, no mess. Just nutrient rich, clean food that fuels their happiest, healthiest days so you get more of them to share together. Sunday Holiday sale is going on right now. Go to sundaysfordogs.com acast50 and get 50% off your first order. Or you can use code acast50 at checkout. That's 50% off your first order at sundaysfordogs.com accast50 don't miss out on Sunday's best sale of the year@ Sundaysfordogs.com Acast50 or use code Acast50 at checkout. Got a new puppy or kitten? Congrats. But also yikes. Between crates, beds, toys, treats and those first few vet visits, you've probably already dropped a small fortune. Which is where Lemonade Pet Insurance comes in. It helps you cover vet costs so that you can focus on what's best for you and your new pet. The coverage is customizable, sign up is quick and easy, and your claims are handled in as little as three seconds. Lemonade offers a package specifically for puppies and kittens. Get a'llemonade.com pet your future self will thank you. Your pet won't. They don't know what insurance is.

[Monday Sidekick / Sleep Number / California Lottery Announcer]

Why choose a sleep number Smart bed.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

Can I make my sight softer?

[Monday Sidekick / Sleep Number / California Lottery Announcer]

Can I make my sight firmer? Can we sleep cooler? Sleep number does that cools up to.

[Workday Go / Earnin / Monday Sidekick Announcer]

Eight times faster and lets you choose your ideal comfort on either side. Your sleep number setting Enjoy personalized comfort for better sleep night Night after night.

[Monday Sidekick / Sleep Number / California Lottery Announcer]

It'S the final days of our Black Friday sale. Recharge this season with a bundle of cozy, soothing comfort. Now only $17.99 for our C2 mattress and base plus free premium delivery price is higher in Alaska and Hawaii. Check it out at a Sleep number store or sleepnumber.com today.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

It may be time to toss out the old good sleep versus Bad sleep idea. A new study from Concordia University suggests that perhaps we think about our shut eye in five distinct patterns that go beyond how long we snoop. News There are a lot of considerations when it comes to studying how we sleep. There's biological factors, sure, but there are also psychological and socioeconomic elements at play. So the team gathered data on the participants, health, cognition and lifestyles to identify five distinct sleep patterns. The study was done using cognitive tests, brain scans and sleep surveys from 770 participants aged 22 to 36. Now, it's important to note that most of the participants worked full time and the majority of them were white, since this study considers the socioeconomic elements of sleep as part of its full biopsychosocial model. And from all that information, they created these five profiles which I'm excited to get into and see which type I fit into. Profile 1 is made up of people who reported low sleep satisfaction and have some psychological distress. Typically, they take a longer time falling asleep staying asleep, and their sleep doesn't feel as deep as it could be. Their cognitive tests showed lower performance as a result, and brain scans showed decreased connectivity between the neural networks involved in self reflection, attention and task management. When it comes to mental health, participants in Profile one were more likely to have depression and anxiety symptoms as well as stress, anger and fear. Profile 2 has people who the researchers describe as sleep resilient, which just means that they didn't have many complaints about their sleeping patterns, but they still had psychological symptoms. They said their sleep was fine, but showed signs of stress, attention problems and lacked the same brain connectivity patterns as the first group. The idea is that people in this group have emotional or psychological challenges, but for whatever reason, it doesn't seem to affect their sleep. Profile three is related to people who frequently use sleep aids, anything from prescription medication to sleepytime tea. They had high satisfaction in their physical health and social relationships, with few complaints about their sleep overall. But they didn't perform as well in visual memory and emotional recognition tasks, and their MRIs showed decreased connectivity in the regions of the brain associated with vision, memory and emotion. The people in Profile four are those of us who get by on fewer than six to seven hours of sleep per night. As you might imagine, their cognitive tests had worse accuracy than those getting more sleep, and they also had a longer reaction time. For tests that looked into emotional processing, language and social cognition. They exhibited more aggressive behavior and lower levels of agreeableness, but their brains showed higher connectivity patterns across brain networks. And finally, we have Profile five, which is made up of participants who have fragmented sleep patterns or wake up a lot throughout the night. This profile was also associated with increased levels of aggression. This group had strong evidence of mental health symptoms like anxiety and substance misuse. Their cognitive performance also wasn't as good as people with more regulated sleep patterns. The researchers note that this information is an example of correlation, not necessarily causation, because they are looking at sleep from a more holistic viewpoint. It's almost impossible to consider all the other elements that factor into these outcomes. The point here is that there are a lot of ways that sleep affects our bodies, our brains, and our mental health, and that when we study sleep, we need to be looking at it from all angles. For Warner Bros. Discovery Curiosity Weekly is produced by the team at Wheelhouse DNA. The senior producer and editorial correspondent is Teresa Carey, our producer is Chiara Noni, our audio engineer is Nick Kharisimi and head of production for Wheelhouse DNA is Cassie berman. And I'm Dr. Samantha Yamin. Thanks for listening.

[Workday Go / Earnin / Monday Sidekick Announcer]

Think enterprise software is too costly, too complex and takes too long to get up and running? Think again. Workday Go makes simplifying your small or mid sized business simple. HR and finance together on one powerful AI platform right at your fingertips. Workday Go gets you live fast and fits the needs of your business. Find out what Workday Go can do for you. Go with Workday Go.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

You know Hannah and I love a good bedrotting session. Reality TV snacks nearby and now I've leveled up with my self care game with this Shark Beauty Cryo Glow, the number one skincare facial device in the us. Wait, I'm obsessed with it. I've had it for a while actually and it's the only mask that combines high energy, LED infrared and under eye cooling. I really need this because nothing wakes me up in the morning. You could do four treatments in one better aging, skin clearing, skin sustain and my favorite the under eye revive with Insta Chill ColdTech. You put it on and it just feels so good under your eyes. Like I actually feel like I got eight hours of sleep. It's truly like a luxury spa moment while you're literally horizontal. It's perfect for post workout Sunday scaries or when you just want to glow while rotting. To treat yourself to the number one LED beauty mask this holiday season, go to SharkNinja.com and use promo code Giggly Squad for 10% off your CryoGLOW. That's SharkNinja.com and use Promo code GigglySquad for 10% off your Cryoglow.

[Workday Go / Earnin / Monday Sidekick Announcer]

You know what's faster than your paycheck? Literally everything. It's time to get your pay up to speed with Earnnin. You can access your pay as you work instead of waiting days and weeks for a paycheck. Get up to $150 a day with a max of $750 between payday. No interest, no credit checks and no mandatory fees. Because I mean, hey, it's your money. Download the Earn it app now to get it and join millions of people making any day payday. That's E, A, R, N I N Earn. It is not a bank access limit. They're based on your earnings and risk factors. Available in select states. Expedited transfers available for fee terms and restriction supply. Visit earn.com for full details.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

Dashing through the store Dave's looking for.

[Monday Sidekick / Sleep Number / California Lottery Announcer]

A gift, one you can't ignore.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

But not the socks he picked.

[Workday Go / Earnin / Monday Sidekick Announcer]

I know. Putting them back.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

Hey, Dave, here's a tip. Put scratchers on your list.

[Monday Sidekick / Sleep Number / California Lottery Announcer]

Oh, scratchers.

[Dr. Jeffrey Eiliff / Curiosity Weekly Host]

Good idea. It's an easy shopping trip.

[Monday Sidekick / Sleep Number / California Lottery Announcer]

We're glad we could assist. Thanks, random singing people.

[Sundaes for Dogs / Lemonade Pet Insurance Announcer]

So be like Davis Holiday and give.

[Monday Sidekick / Sleep Number / California Lottery Announcer]

The gift of Play Scratchers from the California Lottery. A little play can make your day.

[Workday Go / Earnin / Monday Sidekick Announcer]

Please play responsibly. Must be 18 years or older to purchase player claim.