PBS Nova: Mysteries of Sleep

But why?

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.

Why do some people ruminate all night,

and other people,

they see the pillow, they're gone?

Cutting-edge research is now giving us a new view

inside the sleeping brain.

How can we boost and enhance

sleep quality, sleep quantity?

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

If you've ever thought of sleep as a waste of time,

think again.

The more we learn about sleep,

the more we realize that we can't dismiss it.

Getting a good night's sleep

is possibly the single most important thing

you can do every day.

"Mysteries of Sleep,"

next, on "NOVA."

Major funding for "NOVA" is provided by the following:

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.

Why do we spend a third of our lives

in such an unproductive and defenseless state?

What is that thing that sleep does

to our brain and our body every single night

is very much an open question.

A question that has baffled scientists for centuries.

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.

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.

In fact, we find that the brain is just as active

when we're asleep as when we're awake.

's just active in different ways.

You're not either aware or not aware,

you're neither not conscious or unconscious.

It's a whole spectrum.

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.

What we're fast learning

is that sleep isn't a luxury; sleep is a biological necessity.

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.

Sleep is one of the most essential elements of life,

actually.

Sleep and life evolved hand-in-hand.

Evolution has come up with a variety of ways

to get some shut-eye.

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.

But perhaps one

of nature's most innovative sleep solutions

is found under the sea.

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.

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.

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

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

I actually think that the whole night

is a really magical event.

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.

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

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

...with an array of electrodes

to record brain activity.

Yeah. - There you go.

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.

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.

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.

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.

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.

Thousands of neurons, firing in unison.

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.

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.

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.

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.

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.

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.

REM sleep is named

for the rapid eye movements we make when we dream.

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.

As we switch from one dream to the next,