For centuries, we've regarded sleep
as nothing more than a way to recharge our batteries.
But all of that is changing.
If sleep wasn't important,
it is probably one of the most significant mistakes
that evolution ever made.
Once seen as a blank screen,
the sleeping brain is now emerging
as an energetic and purposeful machine.
In parts of sleep, the brain is at least as active
and maybe more active than it is during waking.
Around the world,
researchers are attempting to penetrate
the mysterious world of sleep
and decipher its secrets.
Secrets that could change our lives.
I think that what happens during sleep
permits what happens in the waking brain.
I'm Doctor Jennifer Gardy.
Join me on a surprising odyssey.
This is remarkable.
(laughs) Wow.
From playing Chopin to playing with puppets.
From a city that never sleeps to an isolation chamber
in the Colorado Rockies,
come with me as I begin a journey to discover
why we sleep.
(dramatic music)
Deep in the German countryside
lies one of the unique research centers in the world.
Inside this compound, scientists uncovered
one of the first clues that sleep
might be about more than just conserving energy.
That's very nice.
Doctor Niels Rattenborg has spent a decade
researching here at the Max Planck Institute.
But he isn't your typical sleep scientist.
That's because Dr. Rattenborg doesn't study humans,
he studies birds.
(flapping wings)
Birds are an excellent group of animals
in which to study sleep, because they've evolved
sleep patterns remarkably similar
to those in mammals, including ourselves.
While all animals sleep,
scientists like Dr. Rattenborg now know
that only birds have slow wave and REM sleep
just like us.
It's why he's studying the humble Canada goose.
(honk)
A bird that helped him understand
what evolution revealed about sleep.
Some geese over here.
Yeah.
And he wanted me to demonstrate
what he was the first to discover.
So, you see those geese sleeping?
Yeah.
You think you can sneak up on them?
Seems pretty easy.
Sleeping geese, smart human.
(playful music)
They're starting to look.
But these geese prove far more elusive than I expect.
Whenever I get too close, they wake up
and head for the hills.
I give up, it's impossible!
Some already went back to sleep.
(both laugh)
According to Dr. Rattenborg,
the geese evaded me because of an amazing feat of evolution.
It's called unihemispheric sleep.
Whales, seals, and dolphins do it, too.
While one half of the brain stays awake and alert,
and one eye open,
the other side of the brain is in deep sleep
and the corresponding eye is closed.
Given this extraordinary evolutionary adaptation,
Dr. Rattenborg believes that what's happening
inside the sleeping brain must be vital to life itself.
And he's not alone.
Yeah.
Dr. Sabine Seehagen often spends more time on the road
than in her lab at Ruhr University in Western Germany.
That's because her research subjects
have evolved to spend more time asleep than awake.
Babies nap for up to 16 hours a day
with waking periods lasting for just an hour or two.
From the bird research, it was clear
that sleep was playing some vital role.
Dr. Seehagen wanted to find out if it was
helping babies consolidate and retain memories.
Infants, they have to learn so much
in the first few years of life
and they develop in such striking ways, really,
everyday a bit more.
(baby exclaiming)
We were interested to see whether one function of sleep
might be to facilitate memory processing.
To discover that, Dr. Seehagen
chooses a task that requires baby Moritz
to remember three interrelated steps.
We use a hand puppet
and show them three actions.
We throw them how to take off a mitten,
how to shake the mitten,
and then how to replace the mitten.
What Dr. Seehagen is attempting to do
is trigger the memory processing system.
The hippocampus is located deep within our brain.
This is where specific memories are encoded and stored.
The neocortex is the large, outer part of our brain.
It establishes associations between memories.
Dr. Seehagen and her assistant, Carol,
teach the exact same memory processing task
to several other babies.
(speaking German)
As soon as the testing is over,
some of the babies stay awake,
while others, like baby Moritz,
go down for a nap.
For Dr. Seehagen, this is a rare opportunity
to discover whether the sleeping brain
is doing something unique with the information
it's just taken in.
We were thinking that if sleep really helps them
to retain the memories,
then only those infants who napped right away,
soon after learning, would remember the actions.
Whereas infants who would wait with their nap
would not remember the actions.
Carla hasn't had a chance to nap yet.
Like all of the babies, she has just 90 seconds
to repeat the action she saw earlier.
(Carla cooing)
But Carla shows no sign of remembering the three steps.
(doorbell chimes)
Jonah is another baby who hasn't napped.
Before we started our study there was not
very much knowledge about how sleep
might be important for infants' memories
and I'm very interested to see
that infants who wait with the nap,
they did not show signs of remembering
what we've shown them before.
Across town, baby Moritz is just up
from his four hour nap.
Now it's his turn.
Without any prompting, he gets to work.
And nails it.
(speaks German)
Dr. Seehagen and her colleagues conducted this test
on more than 200 infants
with identical results.
Well, I think it shows several amazing things
about babies, actually.
Until a few decades ago,
many people even doubted whether infants
can form longer term memory.
But I think our study shows that sleep
seems to play a really fundamental role
in early memory processing.
And I mean, that's a very fundamental task for infants
to build long term memories so that they can
use them at a later point.
(classical piano)
George Ko is in the midst of a
Harvard University tradition.
He's cramming.
(classical piano)
George is trying to learn Chopin's third Scherzo,
but he's running out of time.
So this week I got slammed with a lot of work
and I have a performance tomorrow
and I haven't been able to practice much.
For George, the solution is a no-brainer.
So I'm probably not going to sleep tonight.
I'm probably going to hear the birds chirp in the morning.
But if babies need sleep to process memories
and learn, is the same true for adults like George Ko?
(birdsong)
Jen, why don't we put you over here and Jamai, you...
It's a question that drives the research
of Doctor Robert Stickgold.
A really simple test for you guys to do.
Dr. Stickgold is one of the world's leading
sleep scientists.
So, put in your first name or your initials.
To discover whether memory processing
is sleep dependent,
Dr. Stickgold needs to create a complex learning
and motor skill task.
Now, as soon as you press another key you're gonna start.
What he decides on is a very simplified version
of performing Chopin's Third Scherzo.
And your job, take your left hand,
put your four fingers on the keys one, two, three, and four.
You're just gonna type that number sequence
over and over again, four one three two four.
Why don't we just have you both start together now?
Both Jamai and I are going to do this task
a second time, but I'll get to sleep in between
and she won't.
Then we'll see who has the bigger improvement
in speed and accuracy.
It seems hard to believe that just one night of sleep
will help me learn the sequence and make me faster.
But tomorrow will tell.
The next morning, I'm back.
Jamai did her retest yesterday afternoon.
Now it's my turn.
It all comes down to who has improved more.
And here you are.
Let's take a look at this.
Okay.
First, Jamai's results.
On her second trial with no sleep,
look at here, she's shown no improvement at all.
But I was a different story.
Then look at this, you just zoom up there.
You're up to 23.
It's a huge improvement in terms of speed.
It's not just academics and students
who are learning all the time.
We're all learning all the time.
Every time you start your car,
you're learning a little bit more about
how long you have to turn the key,
how much you have to press the gas.
Every time you turn a corner,
you're retooling your accuracy at doing that.
So we're learning all the time and we don't even know it.
When we sleep after learning,
our brain consolidates that memory
so we can retrieve it easily.
The more complex the learning task,
the bigger the benefit we get from sleep.
But when we don't sleep enough
that information never even gets filed.
If you don't get enough sleep
the night after you've learned,
you are not going to show the potential benefits from sleep.
Even if you sleep all you want for the rest of the week.
It has to come in that first night.
So what we're learning is that night by night
we need that sleep or we'd lose.
We'd lose everything.
(classical piano)
I'm not the only one who benefited
from some shuteye.
Instead of pulling an all-nighter,
George Ko went to bed.
According to Dr. Stickgold's research,
it was exactly the right thing to do.
When I tell people that we learn a lot
while we're asleep, they think that's kind of an oxymoron,
that you can't learn while you're asleep.
But in fact, this is just your brain
doing what it evolved to do.
I think the brain carries out its most sophisticated
memory and brain functions while we sleep.
(classical piano)
(seagulls)
Given the power of sleep to help us learn,
scientists at a unique biosphere in Colorado
wondered whether it also had the capability to control
how much we eat.
(electronic music)
What better place to find out why we sleep
than in a city that never does?
Come on!
(cheering)
If there's one place on Earth
where we're willing to sacrifice a little bit of sleep
in the hopes of gaining something better,
it's here, Las Vegas.
But this 24 hour town isn't the only place
we're making this kind of trade off.
Without realizing it, we might be losing something
far more precious than just a few dollars.
Doctor Scott Killgore is a professor of psychiatry.
But he's also a lieutenant colonel in the US Army.
Treating soldiers who fought on the front lines
made Dr. Killgore realize
that they provided a unique window on the world of sleep.
We were doing sleep research
and most people were just focusing in on reaction time
and simple cognitive processes.
But what about this other side of which choice to make?
You know, do you drop the bomb now,
do you pull the trigger, do you not pull the trigger?
Because these are not cold decisions.
You don't make them like a computer does.
They're very emotionally charged situations
and we need more information about how
lack of sleep affects emotional functioning.
At the heart of this quest
lies a seeming contradiction.
As it turns out, our emotions don't cause us
to make bad decisions.
Most of the time they actually help us make good ones.
Every day I make thousands of choices,
many of them intuitively.
My intuition is guided by a special type of memory,
an emotional one.
When I experience something,
my brain flags it as either positive or negative.
When it's time to make a decision,
these emotional memories help me.
If you watch those old Star Trek episodes,
you see that in situations Spock always had
the logical decision making process.
He was like a computer.
So he didn't let emotions affect his decisions.
Whereas, Kirk, he could tap into that gut feeling in the
pit of his stomach and make the right command decision.
To get inside the brain where these gut feelings,
these emotional memories are created,
Dr. Killgore came up with an ingenious experiment
based on a specially designed gambling task.
Now I'm gonna visit Dr. Killgore
and put that task to the test
and this time, what happens in Vegas
won't be staying in Vegas, all in the name of science.
So the basic idea here is that
there are four decks of cards.
Okay.
And your job is to try to win as much money as possible.
Ooh!
And avoid losing any money in the process.
(beeping)
Hello, hundred dollars.
But what no one's told me is that
two of the decks will give me big wins
but even bigger losses.
Hmm.
The other two decks deliver small wins
but smaller losses.
(buzzing)
To come out ahead, I've got to rely on those gut feelings
to help me make the right decisions.
(beeping)
All right, let's see.
Turns out I did all right.
I took home 1200 dollars.
So, this is your baseline.
So now what I want you to do is
to go out and have some fun tonight.
I can do that.
It's time to get sleep deprived.
(laughing)
Yes!
A little over a century ago,
we slept, on average, nine hours a night.
Today that's down to less than seven.
So my night on the town is just a quick way
to get me to where most of us already are,
into a state of serious sleep deprivation.
Jennifer.
Are you still awake?
No sleeping!
Good morning, Doc.
Hey, Jen, how are you doing?
I gotta be honest, I'm really tired.
I think I'm a nine out of a ten on the tired scale.
So, did you get hitched?
(laughs) No.
After 24 hours without sleep,
it's time to do the gambling task again.
Hello, cards.
My old friends.
This time I keep losing track of the decks
and no matter how much I try, I can't seem to stay focused.
Yesterday I won 1200 bucks,
today I lose 800.
Whoa, I sucked.
The reason can be found here,
in my ventromedial prefrontal cortex.
This is where those emotional memories are incorporated
with my reasoning to guide my decision making.
Normally, this area is very active.
But after 24 hours without sleep,
this critical part of my brain has simply shut down.
It's not active anymore.
Yeah.
So it's not able to turn on and integrate your emotions
to guide your cognitions and your thoughts
and your decisions.
So your judgements start to get impaired.
You don't know the right answer,
you can't rely on your gut to tell you,
"That's the way I should go."
Yeah.
It was impossible to tune in onto those,
the good decks and the bad decks.
Right, the ability to integrate the emotions
with decision making becomes affected.
So you just flounder.
What's fascinating is that Dr. Killgore found this
same impaired judgment in people with stroke damage
in this exact same part of the brain.
So, in essence, sleep depravation is almost
a temporary brain injury.
Yeah, it's basically very much like you're
brain damaged, but getting a good night's sleep
can actually reverse the process
and get you back to your baseline.
Well, that's good because you know what I could
use right now is my baseline level.
I would really like to get back there.
By delving deep into our brain, Dr. Killgore
has discovered a direct relationship between
sleep and the emotional switching system
that guides our decision making.
We don't understand everything yet,
but so much of the work that we've been doing
shows that even cutting your sleep down
by a couple of hours
alters the connectivity in the brain
and that in turn affects your emotional intelligence
and your decision making and all these areas in life.
Lights off in three, two, one.
For two and a half years,
volunteers have lived here at the University of Colorado
inside a kind of biosphere.
For two weeks at a time,
they sleep, eat, and work in this lab,
isolated from the outside world.
Everything they do is carefully monitored.
They can't take a nap or eat a calorie
without it being measured.
Hey Chris, let's go in, let's get started.
All right, sounds good.
This experiment is the brainchild of
neuroscientist, Doctor Ken Wright.
If sleep deprivation can cause temporary brain damage,
Dr. Wright wondered if it could also disrupt
another system regulated by our brain,
the one that controls how much we eat.
1.5 billion adults worldwide,
about 150 million school age children
and 43 million preschool children
are overweight or obese.
And over half of our adult population right now
is not getting that minimum of seven hours a night.
(on intercom) Hey gang, just checking in with you.
How's it going tonight so far?
It's going good.
Dr. Wright created this isolation chamber
to take volunteers deep into sleep deprivation
to see if that would have an impact on their weight.
For a week now, this group has been allowed to sleep
nine hours a night.
Okay, big boy, time to wake up.
And eat as much food as they want.
But now it's time for a radical change.
Yeah, what do you think?
The volunteers are about to have their sleep cut
by nearly 50 percent.
For the next week, they'll get just five hours a night.
I'll give you a countdown.
I'll dim the lights and then give you a countdown.
Morning, Jake.
Good morning.
Hey, Chris.
How's the subject going today?
As the 50 percent cut in sleep
begins to take a toll, Dr. Wright notices a change
in the amount the volunteers are eating.
So, as we've been following people's food intake
across these last four days,
we're seeing something remarkable.
Their food intake is going up, so they're eating more.
And not just at mealtimes.
The volunteers are also consuming more snacks.
A lot more.
What we're starting to see is that
they're eating more after dinner
than they do at any meal across the entire day.
So it's as if they're eating four meals a day
rather than just three.
But what's most fascinating for Dr. Wright
is the impact on the two hormones that regulate
how much we eat.
(crunching)
Ghrelin and Leptin are called the hunger hormones.
Ghrelins signals the brain when it's time to eat.
Leptin tells the brain when the body has enough
stored energy and it's time to stop eating.
The lack of sleep seems to be causing a meltdown
in this critical part of our weight regulation system.
As the volunteers eat more,
both Grehlin and Leptin are telling the brain
it's time to stop eating.
But these messages aren't getting through.
And the amount of weight gained by the volunteers
is stunning.
For these participants after just five days
of getting too little sleep,
they gained .8 kilograms.
It used to be thought that sleep was just for us
to feel alert during the day
and for us to think clearly and perform cognitively
at our best,
but unfortunately, when people are not getting enough sleep,
they eat more.
And sleep loss is known now to contribute to that risk
of gaining weight.
People recognize that sleep is something
that they can easily give up.
But when they make that choice,
they're not always thinking about
the long term consequences of that.
While they may get sleepy,
the effects of developing heart disease,
the effects of developing obesity,
those are down the road.
Sleep regulates our weight
and guides our decisions.
But does it have an impact on another key function
controlled by our brain?
Dreaming.
Scientists are now trying to discover
if our dream world plays an important role
in our waking lives.
Dr. Antonio Zadra can't remember a time in his life
when he wasn't intrigued by dreams.
Dreams have always fascinated humankind
and so people have always been curious about,
since the dawn of history, about where dreams come from,
how are they formed, do they have any meaning?
We spend 52,000 hours of our lives dreaming.
Six solid years.
Dr. Zadra is convinced that within this vast ocean
of dreaming lies the key to its function.
To unlock the secrets of our dreams,
Dr. Zadra first had to find a way to enter
this mysterious world.
People like artist James Simon turned out to be the key.
Along with nearly 100 others,
James is part of a unique group.
He is one of Dr. Zadra's dreamers.
But I'm aware in the dream that this raven
has a propensity to lunge for a person's eyes.
As an instinct, as a reflex.
Dr. Zadra has collected and assessed
an astonishing 10,000 dreams from people like James Simon.
He discovered that women have more nightmares than men
and that we dream about different things,
women about relationships and men about calamities.
He's also uncovered that dreams provide a window
into our psychological well being.
The more negative emotions you have in your dreams,
the more negative interactions, aggressive interactions
you have with other characters in your dreams,
the less happy you tend to be,
or the more anxious or depressed you tend to be.
Taken together, Dr. Zadra's discoveries reveal
that dreams are not the random and chaotic occurrences
most of us think they are.
When you look at people's dreams,
you see that there is more order in them
in the sense that you see a continuation
between what's going on during wakefulness
and the content in their dreams.
Both Dr. Zadra and sleep scientist
Dr. Robert Stickgold believe the connection between
our waking lives and our dream world
is a critical clue to the function of dreams.
It's when we sleep and in part when we dream
that we normally figure out what the events of our day mean.
Dr. Stickgold believes this because
of an extraordinary conversation that takes place
inside our sleeping brain.
When we first go to sleep, the memories we've accumulated
during the day flow from the hippocampus,
where they've been stored and assessed, to the neocortex,
where they're associated with other memories.
The neocortex kicks into high gear when we dream.
Then in that first REM cycle,
it's as if the neocortex says back to the hippocampus,
"Oh, that's like what happened last month."
It's as if now the front of the brain
is telling the hippocampus, "Okay, you know what?
Those details aren't important."
Or, "Those details are important."
And telling the hippocampus what to do with that information
and also working out itself, in the neocortex,
seeing how things fit together.
To confirm that dreaming really does help us
associate memories in order to give them meaning,
Dr. Stickgold created a series of unique tests.
In one expermient, Dr. Stickgold trained a group of people
to go through a maze.
Afterwards, half had a nap and half didn't.
Later that day, people came back and ran the maze again.
Those that had napped found the exit more quickly.
But what got Dr. Stickgold really excited
were those people who both napped and dreamt about the maze.
They found the exit ten times faster.
I think what we're seeing now
is that dreams in fact are a reflection
of the kind of processing that the brain does
while we sleep.
Just us being conscious while we're asleep
and conscious of things that our brain is
constructing as stories.
And so we're really watching over the shoulder
of a film editor.
But if you just watch the screen of the editor,
it looks crazy, like a dream.
Things are juxtaposed from different places,
you don't know why they're being juxtaposed.
Things are being replayed.
It's as if the brain, while we're dreaming,
is trying to see how things fit together.
According to Dr. Stickgold,
this is my sleeping brain giving meaning
to the events of my life.
Dr. Zadra believes if patterns can be found in this chaos,
they have the power to reveal something
about my psychological well being.
Before I arrived at his lab,
he asked me to keep a dream diary.
So for the last six weeks, I've been writing down my dreams.
I had a chance to read over your dreams
and try to quantify their contents,
in terms of the characters we see, the settings,
the social interactions.
Dr. Zadra knows very little about me,
only that I'm a TV host.
But right away he uncovers my anxieties about
solving problems in a dream about a leaking pipe.
So there's all the water, which is a misfortune,
not your fault, but you still--
I have to fix it. -: Unplug it.
You still get the towels, you still mop it up.
Yeah.
And so, um, you're still trying somehow
to minimize the damage or to try to
bring it under control to whatever extent you can.
Dr. Zadra also totally nails
that I worry about outward appearances
and about the value of my work.
But there's one revelation from my dreams
that catches me completely off guard.
In over half of your dreams,
there are references to animals.
So the fact that there are many animals
and the way you interact with them,
I would say that you're concerned about
animals' well beings.
Not just your dog or your cat, if you happen to have one,
but that the well being of animals is something
that is dear to you, generally.
This is crazy, you're making me all misty
and teary-eyed, because this is remarkable.
Absolutely remarkable.
I do, I have a cat, I have a dog, I love them to pieces,
I love all animals.
This is remarkable.
(laughs) Wow.
I think this entire exercise for Jen
probably made her much more appreciative
of the power of dreams
and again of the order that we can find in dreams
and the psychological meanings we can find in dreams.
So there's a relationship over time
about how well people are functioning
and how well they feel
and the content and patterns in their dreams as well.
If sleep allows us to enter
the mysterious world of dreams, could it also be involved
in one of the brain's greatest unsolved puzzles?
Every night, virtually every species on the planet
goes to sleep.
For the first time, we're beginning to understand
how this nightly ritual regulates
almost every aspect of our waking lives.
But there's one discovery that's eluded researchers.
Uncovering the core biological function of sleep.
For neuroscientist Doctor Jeff Iliff
and a team from Rochester University,
their quest begins with a baffling clue
about a protein that's the key culprit
in Alzheimer's disease.
So there's a protein called amyloid beta,
which is made in the brain all the time.
Now, when you're awake, amyloid beta levels
in the brain go up
and when you're asleep during the night,
amyloid beta levels in the brain go down.
The question is why.
To find out, Dr. Iliff hopes to do
what few sleep scientists have ever done before.
Look directly into the sleeping brain.
We have a very powerful and specialized microscope
that can actually shine through the skull
into the living brain while it's doing all of its processes.
This is the world of the sleeping brain.
What Dr. Iliff sees is a complex network of blood vessels
that dive deep into the brain's center,
supplying nutrients and oxygen to its cells.
But there's something else, something completely unexpected.
At night, the brain begins to change.
Something's happening within the tissue itself.
The brain's cells, the support cells in the brain,
are actually shrinking.
Dr. Iliff believes the team has
stumbled upon a clue that may be connected
to one of the brain's most puzzling mysteries.
How it cleans itself.
Like the tributaries of a river,
our body relies on the circulatory system
to bring nutrients to its trillions of cells.
But these cells also produce waste.
In a river, sediment settles to the bottom,
but in our bodies, we have lymph vessels
to collect the waste and carry it through our bloodstream
to places like the liver, where it's eliminated.
But there's one part of the body
the lymph vessels don't go to and that's the brain.
So how does the brain clean itself?
Dr. Iliff believes the answer is connected
to the mysterious changes he observed
taking place inside the brain while we sleep.
During the day, the brain is protected by a sac
filled with fluid that surrounds it.
But as Dr. Iliff discovers, at night this sac empties
and the fluid filters through the brain.
What was happening was that
the fluid was piggybacking, using the structure
of the blood vessels to get access to the entire brain.
But it's what the fluid does that provides
Dr. Iliff and his team with an extraordinary breakthrough.
The fluid that's on the outside of the brain,
as it flows along those blood vessels
and through the brain tissue,
it's doing the most amazing thing.
It's clearing away, washing away,
the waste particles in the spaces between the brain's cells.
Wow.
We can't multitask enough during the day,
we have to set something aside.
Housekeeping happens at night.
Yeah, it's a very clever way to do, really,
two things with the same structure,
both provide nutrients and clear away the waste.
But it's unique.
No other part of the body uses a plan like this
to do these two things.
It's a brains cleaning system.
It is.
It's sort of like a dishwasher for the brain.
But Dr. Iliff and his team aren't done yet.
There's still the question of amyloid beta,
the protein that started them on this journey.
Amyloid beta is one of the waste products
produced by the brain.
It's also the same protein that builds up
in the brains of people suffering from Alzheimer's disease.
When Dr. Iliff started this research,
he saw levels of amyloid beta rise in the brain
during the day and drop at night.
Now he knows why.
The brain is washing away this dangerous protein
while we sleep.
So, circling back to the beginning,
what does this tell you about Alzheimer's?
Well, it tells us that this process
may be part of what's going wrong
in patients with Alzheimer's disease.
Worsening sleep quality and sleep duration
are both associated with worsening amyloid plaque burden,
so more amyloid beta building up in the brain.
And so the failure of the brain to sort of
keep its house clean and clear away these things
that it needs to be clearing away during sleep
may actually be setting the stage
for the development of diseases like Alzheimer's disease.
For the first time, we're realizing
that our sleeping brain is the foundation
of almost everything we do.
I think sleep is fundamental to life.
We're recognizing the importance of sleep
for our whole body.
Sleep effects everything.
I think that the occurrence of what happens during sleep
permits what happens in the waking brain
and that you could not have all of the magic
of the waking brain without all of the mystery
of the sleeping brain.
We create the meaning of our lives while we sleep.
And that's phenomenal.
(electronic music)
(thwack)
(applause)