NARRATOR: Sleep-- we all do it.

But why?

MATTHEW WALKER: Sleep remains one of those remarkable puzzles.

We've known the functions of eating, drinking, and reproducing for thousands of years.

However, sleep remains a mystery.

EUS VAN SOMEREN: Why do some people ruminate all night, and other people, they see the pillow, they're gone?

NARRATOR: Cutting-edge research is now giving us a new view inside the sleeping brain.

PHYLLIS ZEE: How can we boost and enhance sleep quality, sleep quantity?

It's really, right now, the tip of the iceberg.

NARRATOR: If you've ever thought of sleep as a waste of time, think again.

RAVI ALLADA: The more we learn about sleep, the more we realize that we can't dismiss it.

DAVID DINGES: Getting a good night's sleep is possibly the single most important thing you can do every day.

NARRATOR: "Mysteries of Sleep," next, on "NOVA."

♪ ♪ ALLADA: I think sleep is one of the most enduring mysteries in all of science.

We spend a third of our lives asleep, in this kind of unconscious, unresponsive, immobile state.

I mean, we can't do any of the things that we think are important for our lives, like eat, care for our young, mate.

NARRATOR: Why do we spend a third of our lives in such an unproductive and defenseless state?

ETI BEN-SIMON: What is that thing that sleep does to our brain and our body every single night is very much an open question.

NARRATOR: A question that has baffled scientists for centuries.

YUVAL NIR: It's like this big black hole.

We don't really understand why is it that we sleep and what happens in our brain when we're asleep.

NARRATOR: But in the last decade, sleep researchers have started to unravel the mysteries of sleep, and what they are discovering is mind-boggling.

♪ ♪ Many people think that when we sleep, we are unconscious, so the brain is sort of shut off.

But the more we explore it, the more it's clear that the brain is not shut off.

GINA POE: In fact, we find that the brain is just as active when we're asleep as when we're awake.

It's just active in different ways.

MICHAEL CRAMER BORNEMANN: You're not either aware or not aware, you're neither not conscious or unconscious.

It's a whole spectrum.

NARRATOR: So, what exactly is sleep?

And why do we need it?

One thing that is for certain, when it comes to sleep, we've got a lot of company.

WALKER: What we're fast learning is that sleep isn't a luxury; sleep is a biological necessity.

POE: I find it fascinating, because every animal sleeps, every animal that we've studied-- from worms to jellyfish to sea slugs.

Even the octopus, whose genome is so different from our own, they sleep about as much time as we do.

(yawning) BEN-SIMON: Sleep is one of the most essential elements of life, actually.

Sleep and life evolved hand-in-hand.

NARRATOR: Evolution has come up with a variety of ways to get some shut-eye.

JERRY SIEGEL: Some animals are vulnerable when they sleep.

And other animals are not.

And the animals that are vulnerable when they sleep don't sleep very much.

If animals live in the open, they obviously have to be alert.

And they can't sleep as deeply.

You know, if a giraffe slept the same way a lion slept, there wouldn't be any giraffes.

Now, on the other hand, there are animals like the big brown bat, which is the champion sleeper-- sleeps 20 hours a day.

It sleeps on cave walls, so it's pretty much invulnerable there.

(dolphins clicking) NARRATOR: But perhaps one of nature's most innovative sleep solutions is found under the sea.

ALLADA: One of the really cool animals that people study is the dolphin, which actually has unihemispheric sleep.

Half of the brain has a sleep-like state and the other half has a wake-like state, so the animal has to have one hemisphere awake.

In fact, if you anesthetize dolphins, they stop breathing.

And in the fur seals, such as the one swimming behind us, when the right hemisphere is asleep, the left flipper, which is controlled by the right hemisphere, is inactive, and the body's posture is asymmetric.

So by looking at a fur seal, you can tell which hemisphere is asleep.

NARRATOR: Fur seals and dolphins aren't alone.

Human sleep is equally complex, weird, and mysterious.

I would say my favorite animal, in terms of how animals sleep, are humans.

Human sleep is very broad.

Each individual has their own personal experiences with sleep.

♪ ♪ NARRATOR: So, what exactly is happening inside our brains when we sleep?

REBECCA SPENCER: We've really entered a different world once we're asleep.

I actually think that the whole night is a really magical event.

♪ ♪ NARRATOR: With the help of volunteers like five-year-old Jaime Lopez, sleep researcher Rebecca Spencer gathers clues to how this magical event unfolds.

Just slip this on, just like last time.

SPENCER: To study sleep, we equip Jaime with a sleep cap...

Shake, shake, shake, shake, shake, shake, shake.

SPENCER: ...with an array of electrodes to record brain activity.

Yeah.

SPENCER: There you go.

NIR: The way our brain supports everything that it does, from controlling our body to regulating emotion, having memories, is through the electrical activity of neurons.

These are brain cells connected to one another via these tiny passages that are called synapses.

One neuron emits a neurochemical called a neurotransmitter to this passage, and it's picked up by the next neuron, much like passing the baton in the Olympics.

NARRATOR: This signal, passed from neuron to neuron, can be picked up by the electrodes in Jaime's cap with one of the most powerful tools in a sleep researcher's toolbox-- the E.E.G., the electroencephalogram.

What this screen is showing is the recordings from each of those electrodes in the cap that we put on Jaime.

Right now, in wake, for instance, you know, you can see the brain waves here.

NARRATOR: The vertical lines on the chart represent five seconds of Jaime's sleep.

What's important is that as you get drowsy, those waves slow down, and they become what we call alpha waves.

NIR: And as the sleep gets deeper, the waves become slower and slower, and in the deepest parts of sleep, activity's dominated by slow waves, these massive waves occurring across the brain that are like a tsunami.

(crowd cheering) WALKER: It's almost like a football stadium, where all of the individuals in the stadium before the game are all sort of speaking to each other at different moments, at different times.

That's what seems to happen when you're awake.

But when you go into the deeper stages of sleep, all of a sudden, the crowd starts to synchronize its activity.

They all start to chant in time.

NARRATOR: Thousands of neurons, firing in unison.

SPENCER: That's your deep sleep.

That's when it's hard to wake you up.

When you wake up someone who's been in slow-wave sleep, and we ask them what they were thinking, they will say, "I don't know, I wasn't thinking anything, "I was asleep-- leave me alone, go away," and they'll push you off.

NARRATOR: But Jaime-- along with the rest of us-- doesn't stay in deep, slow-wave sleep all night.

At a certain point, his brain waves change.

WALKER: After about 50 or 60 minutes, your brain will start to rise back up.

And then it will pop up and have a short REM sleep period.

Turns out that those two types of sleep, non-REM and REM, will play out in a battle for brain domination throughout the night.

And that sort of cerebral war is going to be won and lost every 90 minutes.

NARRATOR: We spend most of the night in non-REM sleep.

The rest of the time we spend in the mysterious stage of REM sleep.

It's hard to investigate REM sleep without investigating dreams, because more than 80% of REM periods would include a dream.

SPENCER: Dreams tend to be emotional.

One idea is that we dream to simulate potentially negative events so that we're prepared for them.

♪ ♪ I had a dream, when my daughter was very young, that she fell into the swimming pool-- she was near drowning.

After that, I put my daughters into swim lessons, and water safety has been important to me.

VAN SOMEREN: It's not that we do not dream in the other sleep stages-- we do-- but the most vivid ones are in, in REM sleep.

NARRATOR: REM sleep is named for the rapid eye movements we make when we dream.

NIR: We believe that every time the eyes move in a dream, it's a special moment where we sort of switch to the next dream scene, if you will.

NARRATOR: As we switch from one dream to the next, our brain waves are doing something downright strange.

SPENCER: With REM sleep, the brain waves look just like waves from when you're awake.

We have this paradox that it's a state of sleep, but yet our brain is in a state of activation.

NARRATOR: But perhaps the strangest feature of this stage of sleep is what's happening in your body.

NIR: During REM sleep, our brain actually sends the instructions to the different muscles to move our body as if we were awake.

But lower down in the brain stem, these instructions are disrupted.

They are not relayed to the body, and the body remains paralyzed.

Otherwise, if we had a dream where we fly above the city, we would literally jump out of the window.

NARRATOR: From the dreams of REM sleep, we cycle back into non-REM sleep, including the deepest stage of sleep, slow-wave.

WALKER: In the first half of the night, the majority of those cycles are comprised of deep, non-REM sleep.

Yet, as you push through to the second half of the night, now that ratio balance shifts; and instead, the majority of those cycles are comprised of much more rapid-eye-movement sleep-- dream sleep-- and a lot less deep, non-REM sleep.

DINGES: What is crazy about this is, the pattern is so absolutely reliable in virtually everybody, every night.

It speaks to a fundamental, genetically driven program that is essential for being a human being.

You have to go through this.

NARRATOR: But if every one of us needs a night full of both slow-wave and REM sleep, why is it such a struggle for so many of us to get some shut-eye?

The search for answers has become a multibillion-dollar industry, selling us everything from sleeping pills to ergonomic pillows.

And if they don't do the trick, there are more than 3,000 sleep clinics nationwide, a number that keeps on growing.

Are you up all night tossing, turning, mind racing, trouble getting to sleep, trouble staying asleep?

NARRATOR: Drew Ackerman has created a podcast to help the sleep-deprived get their Zs.

The idea for the show really sprang from my childhood insomnia.

When I was a kid, I lost the ability to fall asleep.

For me, it was anxiety-related.

My parents tried to help, but because they could sleep, I think there was, like, this disconnect.

It's, like, "Oh, try to relax, try to just think about something nice," and I just couldn't do that.

Whatever's keeping you awake, thoughts, you know, things you're thinking about... NARRATOR: Drew's goal is to be as boring as possible.

I'm going to tell you all a bedtime story.

I want you to get comfortable.

ACKERMAN: The podcast is not straightforward, it's full of nonsense.

I have a unique hobby, my dog and I.

We listen to recordings of people knocking on doors.

ACKERMAN: It gives people permission not to listen, or to only kind of listen.

I want no social pressure on the listener to pay attention to me at all.

NARRATOR: And there's no shortage of people eager to tune out.

Each month, the show gets downloaded a little bit over three million times.

What I'm going to do is, I'm going to send my voice across the deep dark night.

ACKERMAN: People that listen to the podcast share that feeling-- I don't know if desperation might be a strong word-- but that feeling where you're just lying there in bed, and you feel alone.

How many people listen to the podcast because they have trouble falling asleep?

Like, if you want, raise your hand.

NARRATOR: Having trouble falling asleep or staying asleep are symptoms of the most common sleep disorder on the planet.

Ten percent of all people suffer from chronic insomnia.

VAN SOMEREN: Insomnia is a 24-hour disorder.

It's not only sleep complaints, these persons also feel tensed all day.

It's not that common that you're a very happy, completely unanxious insomniac.

LAB ASSISTANT: Are you ready?

Right.

NARRATOR: Is there a way to decode what goes awry in an insomniac's brain?

On the outskirts of Amsterdam, at the Netherlands Institute for Neuroscience, Eus van Someren is trying to find out, with the help of lifelong insomniacs like Reiny Metz.

METZ: I drop off to sleep very easily.

But after two hours, I wake up, and then it's difficult to go back to sleep.

If it's one night, well, I can manage that.

Two nights is okay, but when it's five nights in a row, it's a bit much, and then you get very, very tired, not only physically, but also mentally.

It makes me anxious, or angry, or, you know, frightened.

NARRATOR: Reiny sleeps in Eus's lab, wearing a high-tech E.E.G.

net that contains hundreds of more electrodes than you'll find in the standard cap.

VAN SOMEREN: We measure sleep overnight with a special E.E.G.

net with 256 E.E.G.

channels, and they cover all of the head.

NARRATOR: The more electrodes he uses, the more activity he can record-- more clues to what's going on in Reiny's brain.

VAN SOMEREN: Okay, Reiny, we recorded your E.E.G.... Yeah.

...during your sleep.

NARRATOR: The next morning, he shows her the results.

So, you go into REM sleep here.

Yeah.

And REM sleep is the part of sleep where the most vivid dreams are.

Now, what I wanted to show you is that, you see that it's not many seconds into REM sleep, and then already something is happening here.

Well, you recognize it.

I don't have to explain that this looks different than this.

Oh, yes, certainly.

It's just maybe two seconds or so that it's really, it's off, it's different.

And this is what we call an arousal.

Yeah.

Where you exchange sleep for something that's really wake-like.

And this is something that is so typical for people like you that sleep bad.

But you do see this in many patients.

Yeah.

METZ: Okay.

VAN SOMEREN: Usually, if you had a good sleep, if you slept on it, as we say, things feel a bit better.

But if there is this profile, that there is some restlessness... Yeah.

...occurring during REM sleep, then, for some reason-- we try to find out-- this whole process of feeling better the next day doesn't work as well.

♪ ♪ VAN SOMEREN: What we observed, which was fascinating, if we add up all the pieces of sleep as suggested by the E.E.G., many people with insomnia have about six-and-a-half, maybe seven hours of sleep, but this is not how these people experience it.

Maybe they just experience large parts of the night really as ongoing rumination, worrying, thinking.

So, it may not feel like a good night of sleep, but it's not the same as being completely sleep-deprived.

NARRATOR: So, is there a connection between these disruptions in REM sleep and the anxiety so many insomniacs feel when they're awake?

To try to find out, Eus comes up with an out-of-the-box idea, based on personal experience.

Back in the 1990s, Eus played guitar in a popular Dutch rock band.

VAN SOMEREN: I remembered a few things from being in the recording studio.

I heard my own guitar playing, and even if it was a tiny little bit, you know, off-tune, it made me shiver.

NARRATOR: Embarrassment is a powerful emotion.

He decides to put it to a test.

(singing out of tune) NARRATOR: A karaoke test.

VAN SOMEREN: We asked people to sing along karaoke, but they couldn't hear themselves sing.

If you don't hear yourself well, it's also difficult to correct if you go out of tune.

Um, you hear that over the headphone, you have the headphone on... NARRATOR: He does the same thing with good sleepers.

Next, Eus puts them in an fMRI.

VAN SOMEREN: So, in the MRI scanner, we had them listen to their own embarrassing singing.

(Metz singing out of tune on speaker) NARRATOR: As Reiny listens to her singing, the fMRI detects activity in a part of the brain called the amygdala.

We have two, one in each hemisphere.

VAN SOMEREN: I sometimes call the amygdala the siren of the brain or the alarm bell of the brain.

So, if there is something that we should pay attention to, because it's dangerous or important, then the amygdala activates.

(Metz singing out of tune on speakers) VAN SOMEREN: So, they heard themselves sing really, really out of tune.

Their amygdala was very upset about that, so, you know, the alarms went off.

METZ (on recording): ♪ Gloria ♪ NARRATOR: The alarms go off for both insomniacs and good sleepers.

This is no surprise for Eus.

But his test isn't over yet.

VAN SOMEREN: We ask them to stay all night in the sleep lab, and we did the same the next morning.

We again put them in the MRI scanner.

Good sleepers, it was not that bad anymore.

NARRATOR: A good sleeper's amygdala calms down.

But that doesn't happen in the insomniac.

VAN SOMEREN: For them, the story was very different, because the more REM sleep they had, the worse it got.

So, instead of the amygdala becoming adapted overnight, many people with insomnia, the next morning, the amygdala could even ring much louder.

You're just loaded with distress that you take to the next day and the next day and the next day.

♪ ♪ If we could change that restless REM sleep, maybe this will help people get rid of distress.

NARRATOR: But insomniacs aren't the only ones to suffer from restless REM sleep.

Researchers are also exploring its impact on post-traumatic stress disorder.

GEHRMAN: PTSD is essentially a memory-based disorder.

An individual has one or more very stressful, traumatic experiences, and they become fearful of anything that reminds them of that trauma.

NARRATOR: Like the smell of a wildfire or the deafening sounds of combat-- traumas so powerful, they can even haunt us when we sleep.

POE: People with post-traumatic stress disorder, they're afraid to go to sleep, or they don't sleep very well because of the nightmares.

♪ ♪ GEHRMAN: Once these nightmares get established, they often can persist for, for decades.

NARRATOR: In her lab at U.C.L.A., Gina Poe is searching for ways to prevent these recurring nightmares from taking shape.

POE: One of the things that we have to do to study the effects of trauma on sleep is, we have to expose animals to a traumatic stressor.

How you doing?

POE: It's the least favorite part of my job, but there's no other way to study it.

NARRATOR: The rats are placed in a chamber where they hear a tone... (tone beeps) Followed by a shock.

It certainly is not a strong enough shock to cause them harm or blister their feet or anything, and it only lasts one second, but it's enough to make them squeak and jump, to say, "What, what was that?"

NARRATOR: Over the next hour and a half, the rats hear the tone and receive the shock.

POE: So they associate that tone with the fear of being shocked.

NARRATOR: Then they're taken back to their nests to get some Zs.

But their sleep is anything but restful.

POE: We have found that the REM dream state of sleep after a rat has experienced a trauma can be hyperactive.

It's kind of like REM sleep on steroids in the way that it is in people with post-traumatic stress disorder.

NARRATOR: So Gina comes up with a novel idea.

After the shock, half the rats go right to sleep.

The other half are kept awake for about six hours.

In that time, they eat, they play, and get a chance to calm down before they, too, get some shut-eye.

POE: The next day, we bring them back into a slightly different environment.

So, it smells different, it has different colors, different lighting.

NARRATOR: In fact, the only thing that remains the same is the tone that came before the shock.

(tone beeps) When the rat that went straight to sleep hears the tone, it freezes.

POE: As soon as they hear the sound, animals with PTSD will freeze.

NARRATOR: But what happens to the rat that's been allowed to calm down before going to sleep?

Will it have the same response?

(tone beeps) When it hears the tone, it also freezes-- at first.

But then it seems to realize the shock isn't coming.

And it will start walking around and sniffing and exploring, as rats normally do.

Because they realize they're not going to be shocked here.

NARRATOR: Delaying sleep after a trauma may lessen the impact of disturbing experiences and even prevent the nightmares of PTSD from taking shape-- that is, in rats.

But will it help us humans?

Gina is taking her work outside the lab, conducting a study with firefighters, asking them to delay sleep after a traumatic event.

POE: With firefighters, we can ask them to do whatever it is they do to best relax and calm themselves after a trauma.

For some, it might be meditation or prayer.

For others, it might be listening to music that they love or going for a run.

We're going to see if that helps us prevent post-traumatic stress disorder.

♪ ♪ ZEE: I used to be asked a lot, "Why do you sleep?

What's the function of sleep?"

But I think we should be asking the question, "What are the functions of sleep?"

NARRATOR: We spend about 20% of the night in REM sleep.

The rest of the time, your brain is in non-REM sleep, part of which is spent producing those big, slow waves.

But what are they for?

One of the first scientific experiments to find clues was conducted back in 1924 at Cornell University by psychologists John Jenkins and Karl Dallenbach.

Using a group of college students as guinea pigs, they found that when their students learned something new, they had a much better chance of remembering it if they slept on it.

WALKER: So, they found that sleep-- rather than simply being a dormant state where nothing too much happens within the brain-- sleep may be important for memory.

But then it raised all sorts of questions about why, and so we've been trying to answer the question of why since then.

NARRATOR: At the University of Arizona, experimental psychologist Rebecca Gomez, along with grad student Katherine Esterline, search for the "why" with the help of a younger generation of students.

(crying) NARRATOR: Toddlers.

Three, four, five.

ESTERLINE: Are you ready?

Yeah!

NARRATOR: How does sleep help them learn and remember new words?

Wow, a zet.

GOMEZ: We're teaching children novel words for completely novel objects.

Look at these.

GOMEZ: We use this completely new information so we can measure the brain's ability to form completely novel, completely new memories.

Hey, a beev.

GOMEZ: So, in essence, we're measuring brute-force memory.

What's this?

NARRATOR: The kids are shown four objects they've never seen before that have been given nonsense names like zet... A zet.

NARRATOR: Mup...

Cool, a mup.

NARRATOR: Beev... Hey, a beev.

NARRATOR: And toap.

A toap.

Toap.

NARRATOR: They get a chance to look at the objects.

Look at these.

NARRATOR: And even touch them.

Then, half of the toddlers go home for their afternoon nap, while the other half don't nap for hours-- or perhaps not at all.

The next day, they're back.

ESTERLINE: Where's the zet?

NARRATOR: How much do they remember?

GOMEZ: What we found is that the children who nap soon after learning... ESTERLINE: Mup.

GOMEZ: ...remember the words about 80% of the time.

Toap.

Where's the zet?

GOMEZ: In contrast, the kids who went through a long period of time before they napped... Where's the zet?

GOMEZ: ...only remembered the words about 30% of the time.

Where's the toap?

This?

GOMEZ: So, you see a huge difference between 80% of the time and 30% of the time, and that's the difference the nap makes.

Where's the mup?

Right here.

NARRATOR: Why did a nap make all the difference?

The key lays inside a tiny organ found deep within the brain-- the hippocampus.

We have one in each hemisphere, and they play a critical role in helping us learn and remember.

So, think of it this way.

I have a little filing drawer beside my desk.

And, throughout the day, as papers come in, I toss them in this drawer.

It's my mail that came today, it's some papers that I had from a class.

That's my temporary storage.

The hippocampus is like that short-term filing drawer, a mishmash of information getting squeezed in, and there's a limited amount of room there for that.

But at the end of the day, I could take that information and turn around to my whole huge filing cabinet, which in this case is the cortex.

The cortex, it's bigger, and it has a really nice sorting mechanism.

You can sort things by their visual components, by their auditory components.

That memory becomes easier to find.

So the role of slow-wave sleep is to take that information that's been stuffed into the hippocampus and help move it to its more efficient filing system out in the cortex.

WALKER: Things that you learned yesterday are now transferred to a safer storage location.

But second when you wake up in the morning, your hippocampus has now been cleared out, and you have a refreshed capacity for new-file acquisition all over again.

NARRATOR: And that brings us back to our toddlers and the power of the midday nap.

Why does it make such a big difference?

Why is it so important for toddlers to clear out that short-term filing drawer?

Researchers have a theory.

GOMEZ: Young children, their brains are still developing, and in fact, the hippocampus is still in the process of developing all across the childhood years.

So it does seem that the hippocampus, when it's young and immature, such as in infancy and early childhood, perhaps those memories need to be stored more frequently or moved to the cortex more frequently.

♪ ♪ NARRATOR: But that doesn't mean naps are just for kids.

SPENCER: It's interesting to think that as you get older, you actually see napping start to return in a number of individuals.

NARRATOR: And there may be a good reason why.

SPENCER: Most older adults report two frustrating things about aging-- "I can't remember things like I used to, and I can't sleep like I used to."

Napping could be one way of helping maintain memories.

There are probably multiple different reasons why the aging brain simply can't learn and remember as effectively.

And I think we're identifying that sleep is one of those critical ingredients.

So, this is the sleep of an older adult.

You should start seeing these waves slowing down and getting higher in amplitude.

That would be what we're looking for for slow-wave sleep.

And so far, I'm not seeing any.

Still looking.

They're asleep, but they're not getting the slow wave that, in a young adult, you might expect to see by now.

WALKER: And it seems to be that the quality of the sleeping brain waves that you have, the depth of those brain waves, and the sort of, the size of those brain waves accurately predicts how well you're able to hit the save button on those memories.

NARRATOR: Is there a way to improve those big, slow waves to increase our ability to hit that save button?

Sleep researchers are exploring a radical idea.

ZEE: One of the things that we're most interested in is, how can we boost and enhance sleep quality, sleep quantity, by using, you know, not pharmacology, but sound.

NARRATOR: 80-year-old Marion Smith is participating in a sleep study.

To track the quality of her slow waves, a single electrode is placed on her forehead.

Marion will hear carefully timed pulses of sound through this headband equipped with tiny speakers.

Well, have a good night, I'll see you tomorrow.

♪ ♪ ZEE: Our patient, Miss Smith, is now clearly sleeping.

She is now getting deeper sleep.

NARRATOR: By examining the brain waves produced by a single electrode, Phyllis has all the information she needs to assess the quality of Marion's slow waves.

ZEE: These are these big, slow waves, but there are very few of them.

And this is quite typical of an older person who has low-amplitude slow waves, and they don't occur, like, in a train.

NARRATOR: Next, a specially designed computer algorithm measures the waves to determine the best time to deliver a particular sound... (sound pulsing) ...the pulsing of pink noise.

ZEE: And we do very brief, like, 50 milliseconds of this very short burst of pink noise.

And we do it five on, five off as long as the person is still in deep sleep.

(sound pulsing) NARRATOR: Think of the sound waves produced by pink noise giving Marion's brain waves a little push, like a kid on a swing or the movement of a ball in a balance pendulum.

WALKER: And what you try to do is sing in time with these brain waves.

But by stimulating them, you're trying to boost the size of those brain waves.

ZEE: It's beautiful.

This is what we want them all to look like, these very large, with strong upstate waves.

Even after you stop stimulating, you can see the increase in these slow waves.

NARRATOR: Phyllis is finding that a little push goes a long way.

ZEE: What we're seeing here is not only that we can increase the amplitude-- that means the height of these slow waves, which is really important-- but we can also increase the train.

So, we could prolong the amount of slow waves.

Which is wonderful, because it's hopeful that the brain, even if you're old, is capable of boosting these slow waves.

NARRATOR: Not only might boosting slow waves improve memory, new research is revealing that during this stage of sleep, the brain may be doing some critical housekeeping.

It was discovered that the brain is actually actively flushing out cellular waste while we sleep.

Just like when we visit Paris, and we see them clean the streets at 5:00 a.m., our brain, it cleans out all the waste during this offline period.

SPENCER: There could be a potential link between sleep and neurodegenerative diseases, like Alzheimer's disease.

And it could all come down to this brain-cleaning process that happens specifically during slow-wave sleep.

ZEE: We have to do a lot more work in this area.

It's really, right now, the tip of the iceberg.

NARRATOR: While researchers explore new ways to help us get the sleep we need, millions of Americans fight the urge, staying up way past bedtime, lured by the trappings of technology.

DINGES: Nearly everyone sooner or later will experience some sleep loss in their life.

The invasion of television into the home 50 years ago, and now computers and telephones, basically, we need to shut that stuff off.

WALKER: Somewhere between infancy and even childhood, we in Western, industrialized nations, we start to abandon the notion that sleep is useful, and, if anything, take the opposite approach and believe that sleep should be short-changed.

NARRATOR: Back in 1964, 17-year-old Randy Gardner broke the Guinness world record for staying awake 11 days straight.

ANNOUNCER: One of these young men holds an unusual world record.

What is your name, please?

My name is Randy Gardner.

My name is Randy Gardner.

NARRATOR: The experiment won him first place in his high school science fair and caught the attention of a nation.

BRUCE McALLISTER: He ended up on "To Tell the Truth," you know, a TV show.

And supposedly the most written-about story in the world after JFK and the Beatles.

Number Two, how did you pass the time when the other people were sleeping?

Well, there were always, there was always someone with me, the two boys that helped me-- one would sleep, and one would stay awake with me.

(chuckles) NARRATOR: Bruce McAllister was one of those boys.

It wasn't the science of it that interested the world.

The world was interested in the drama.

♪ ♪ NARRATOR: The experiment moved beyond high school science when sleep researcher William Dement joined the team.

McALLISTER: And he brought a portable E.E.G., which no one had ever seen before.

They sent the E.E.Gs.

to a supercomputer, a Cray computer in Arizona, and that computer concluded that his... Parts of his brain were sleeping while others were awake.

His brain was catnapping in pieces.

That is how the human brain survived this.

NARRATOR: While Randy looked wide awake, parts of his brain weren't-- what neuroscientists now call a microsleep.

NIR: A microsleep is something that may happen after we've been awake for a very long time, and our brain needs sleep so desperately that we may fall for a very short interval of three to 15 seconds, just... And we've all seen this when our eyes shut down, and we nod to sleep for just a few seconds like this.

♪ ♪ DINGES: We're all very polite and sort of pretend we don't see it, but as we're talking to someone and they start to fall asleep, we notice that they're losing muscle tone, so they start to slump, and the head will start to fall over, and the eye, the lids are coming down, and then we'll see the eyes roll in the head.

If you're holding a steering wheel and driving, you might notice that your arms are starting to slack a little bit on the wheel.

BEN-SIMON: It only takes 200 milliseconds when you're not paying attention that the car is going in the wrong direction.

NARRATOR: When you're sleep-deprived, your brain will fall asleep-- whether you notice or not.

♪ ♪ That's because biology takes the wheel.

Two different processes drive you to sleep.

The first is your circadian rhythm, your biological clock.

ALLADA: One of the signals that's keeping you awake during the day is the circadian clock.

Think of the circadian clock as kind of an internal alarm clock.

NARRATOR: Back in 1938, in a landmark experiment, sleep researcher Nathaniel Kleitman takes one of his students to live in an underground cave.

They spend a month without sunlight, testing the power of that internal alarm clock.

♪ ♪ Even without light, the clock keeps ticking.

But add light, and the cycle can shift.

ZEE: Every day, you get a little light in the morning, it moves your clock in one direction.

You get a little light in the evening, it moves your clock in the other direction, so it can delay and advance.

And by doing this, it maintains your internal clock in synchrony with that of your external environment.

NARRATOR: This clock controls the release of a key chemical that has the power to make you feel sleepy: melatonin, also known as the hormone of darkness.

ZEE: Melatonin goes up at night, and it stays up during the entire night until probably the early morning hours, and then begins its decline.

By the time that we normally would be waking up, melatonin levels are very, very low.

♪ ♪ NARRATOR: But sleepiness isn't just controlled by melatonin.

Another chemical, called adenosine, may also play a role.

Some researchers believe it starts to build from the moment you wake up, and, like an hourglass, fills with the passage of time, gradually increasing our need for sleep, called "sleep pressure."

BEN-SIMON: We see a very strong association between the levels of adenosine and being sleepy and between the level of sleep and reducing that adenosine.

Sleep is the perfect way to clear adenosine from the brain and start fresh.

Many of us are trying to block the effects of that adenosine every day by our consumption of caffeine.

Caffeine binds to these adenosine receptors, so it kind of blocks the effects of sleep pressure, so that we're, we're not feeling it.

It's still there, but we're just not feeling the effects of it.

♪ ♪ NARRATOR: But drinking coffee will work for just so long.

PAUL: If you choose not to go to sleep tonight, and you stay up all night, that sleep pressure will continue to build.

And as that sleep pressure builds, it will impair your thought processes, it will impair your memory.

ZEE: More than 60% of our population may not be getting sufficient amount of sleep, but also sufficient quality of sleep.

NARRATOR: For firefighter Matt Reinhold, who often works a 72-hour shift... (alarm chiming) ...a good night's sleep is hard to come by.

REINHOLD: The alarm will go off and the lights will come on.

(snaps fingers): It's a, it's a startlement.

You know, right off the bat, you're woken up.

There's times where we'll run five, six, seven, eight calls after midnight.

I have never been in a deep sleep here at this firehouse.

Fatigue starts to set in.

All I want to go and do is go lay down, but then the alarm's going off again for a medical down the street.

Lack of sleep definitely makes you more snippy, you become more agitated, more irritated.

The communication factor may go out the window, because you don't want to talk, because you're tired, because of what you're afraid of what you might say.

The irritability takes a toll.

There was a study that compared a group of participants only allowed to sleep for five hours a night, and then there was another group that were allowed to sleep for the whole eight hours, but were woken up every now and then and kept awake for an hour.

And after four days like this, the effects on mood and anxiety were actually much stronger in the interrupted group.

NARRATOR: Sleeping in fits and starts wreaks havoc on your entire system.

DINGES: That fragmenting of sleep is extremely destructive for wake functioning and health.

It is almost as though you didn't get sleep.

So, the consolidation of sleep is easily as important as the duration of the sleep.

NARRATOR: Quality is as important as quantity.

PAUL: There's something about the loss of sleep that breaks down your mind and your body.

If you lose sleep, you will experience memory deficits, and you will experience cognitive deficits.

However, there's also an interesting caveat to that: losing sleep may affect one person one way and another person another way.

There are some individuals which tend to be resilient against the negative effects of sleep loss.

One of the current focuses of our field is to understand the cause of that resilience and whether there is a genetic component.

NARRATOR: Could the ability to recover from sleep loss be determined by our genes?

In 2017, the Nobel Prize in Physiology or Medicine was awarded to three scientists who discovered a group of genes that drive your biological clock.

PAUL: There are genes such as the clock gene, the period gene, the cryptochrome gene.

NARRATOR: But the gene that intrigues neuroscientist Ketema Paul is called BMAL1.

For those of you that know that clocks used to have gears, BMAL1 is the primary gear of the clock.

NARRATOR: In his lab at U.C.L.A., Ketema is exploring the role BMAL1 may play in our ability to recover from sleep loss.

To do it, he makes use of a classic memory test.

PAUL: You put a mouse in an environment and present two objects.

NARRATOR: In this case, two orange blocks.

The mouse spends time getting familiar with them.

PAUL: After that, we take them out and sleep-deprive them for six hours.

NARRATOR: While the mouse is kept awake, one of the orange blocks is replaced with a new object, a blue cylinder.

After six hours, the sleep-deprived mouse is put back in the chamber.

Like humans, mice are naturally curious-- they're drawn to new things.

So a well-rested mouse will spend more time exploring the new object, the blue cylinder.

But that doesn't happen with this sleepy mouse.

PAUL: If you sleep-deprive a mouse, and you put it in the same environment, it will spend equal amounts of time between the familiar object and the novel object, because its memory of the familiar object was impaired by the sleep loss.

NARRATOR: It seems not to remember the orange block.

But what happens if Ketema repeats the memory test with a mouse that has been genetically modified to express higher levels of BMAL1?

Will this dialed-up mouse have a better memory?

Or will the results be the same?

PAUL: The mouse is now exploring the area in which the novel object is in.

Another approach to the novel object.

More exploration around the arena.

A third approach to the novel object, sniffing, exploring the novel object.

So the mouse is clearly spending more time with the novel object, and it suggests that the sleep deprivation did not impair the memory of this mouse, which suggests that overexpressing BMAL1 does make that mouse resilient to sleep loss, and it preserves its memory after sleep deprivation.

NARRATOR: But this is not the only surprise, because it turns out BMAL1 works in mysterious ways.

PAUL: So the B in BMAL1 stands for "brain," the M in BMAL1 stands for "muscle."

NARRATOR: BMAL1 is a gene that's found in the brain and in skeletal muscle.

And the resilient mice were ones that had BMAL1 boosted in their muscles, not in their brains.

PAUL: The result we got was really a surprise.

Sleep is a mental process.

And that's kind of, as a trained neurobiologist, how I had been looking at it before that.

NARRATOR: As Ketema continues his research, he will try to find out how genes in skeletal muscle could influence how we sleep and store memories.

PAUL: Hopefully this will lead to more effective therapies for people that are unable to get sufficient sleep and people that need to function in spite of not getting enough sleep.

NARRATOR: Because when it comes to not getting enough sleep, the people hardest-hit are often the ones we depend on the most.

Sleep deprivation of first responders leads to issues of increased isolation and depression and has enormous impacts, not on just your psychology, but on your physical well-being, as well.

NARRATOR: Former E.M.S.

worker Susan Farren and retired firefighter Ron Shull are working with first responders, educating them on ways to manage their sleep, on and off the job.

SHULL: We want to give you guys some tools and some techniques and modalities to kind of help you sleep better.

NIR: In the last ten or 20 years, we've discovered that sleep is essential for proper brain function.

It's important for our health, for our immunity, for our memory... Toap.

NIR: ...and for our well-being.

SPENCER: I think that's where the phrase "sleep on it" comes from, is that we wake up, and we think differently about a problem.

We think differently about that person that we were angry at.

We just generally feel better about our day if we've had a really good night's sleep.

I think sleep's one of the sweetest things you can get.

It's like a great meal or seeing a good friend.

PAUL: As a citizen in our society that wants people to be safe, the best thing I can say is, "Don't sacrifice your sleep.

"Protect your sleep like you protect your food, "like you protect your resources, "like you protect your environment.

It may save your life."

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