NARRATOR: Too often, we take our bodies for granted,
but under pressure, our bodies can show us
how extraordinary they truly are.
This complex machine grew
out of millions of years of evolution.
So intricate, we're still mystified
by many of the things going on inside us.
A hidden world,
but one we can now explore in 3-D as never before.
Sensations keep us alive,
letting us see, hear' and touch our world.
They begin beneath our skin.
More than a million tiny sensors feed us raw data.
45 miles of nerve fibers let us respond at incredible speed.
Our sensations warn us of danger.
When we're attacked, they're our first line of defense.
They let us perform extraordinary feats.
Sensations will even save our lives
when we're pushed to the limits.
[ l ndistinct radio chatter ]
l n the teeth of a storm,
a pilot guides a 7-ton machine with unerring precision.
Achieving this tests the body's sensory system to the extreme.
Caught on camera by the Coast Guard,
two boys face certain death.
Just off the Oregon coast'
fierce currents have stranded them, and the tide is rising.
We were out maybe 1 /4, 1 /2 a mile, something like that'
and we swam for about an hour trying to get to a rock.
MELOCH E: l was just getting exhausted
and l thought l was gonna die and l thought l was gonna drown.
Didn't believe it.
NARRATOR: Their only hope is a helicopter.
$9 million worth of high technology.
But with winds battering the chopper'
what matters more to the boys
is a mechanism far more complex than any helicopter.
Half a million microsensors
linked to one of the most sophisticated
com munication systems on the planet.
You'll find it beneath your skin.
We're equipped with a forest of amazing devices,
including touch receptors sensitive enough
to feel a single beat of a fly's wing.
Pilot Matt Gingrich needs all his sensors on full alert
to save the boys.
G l NGRl CH: We had about 30-knot winds with the rocks around us.
lt's nerve-racking. very nerve-racking.
NARRATOR: Each square inch of Matt's hands
holds 600 touch sensors.
Some, near the surface, record the lightest of contacts.
Others lie deeper and measure harder' sustained pressure.
Through a web of nerves, they fire signals to Matt's brain.
l n fractions of a second, the brain signals motor nerves,
triggering precise movement of his hands on the controls.
4,000 nerves direct each hand
as he holds the chopper steady above the rocks.
At the same time,
Matt's other sensors are ham mering him with information.
He must read data from a dozen instruments
and watch the horizon.
He must listen to the crew, who can see what's going on below.
MAN: We're going down. Hold position.
Amid all this, Matt's sensory system
must calculate and balance altitude, speed, and position.
That means outperforming any computer on Earth.
MAN: Easy, back. All right' l have the pick-up signal.
We still don't have a machine that has the breadth
to be able to do all of those different things
and, at the same time, instantaneously is assessing
the outcome of each one of those things.
MAN: Right' 30.
F orward, 1 5.
NARRATOR: The speed of signals in Matt's nerves
is crucial to his actions.
MAN: They're right there. You're doing perfect.
NARRATOR: lt keeps the rescue swim mer
from crashing into the rocks.
MAN: Hold it right there. Hold position.
NARRATOR: What's surprising
is the nerve structure that makes the speed possible.
Our nerves are bundles of thin cells,
some more than 3 feet long,
carrying electrical signals to and from the brain.
As insulation protects electrical wiring,
a sleeve of fat surrounds key nerves,
and it's this fat layer
that keeps signals from interfering with one another
so they can rocket around Matt's nervous system
at over 250 miles per hour.
MAN: Easy, back and left. very easy, back and left.
We don't want to get in this wind.
NARRATOR: With the rescue swim mer
dangling close to the rocks,
this is the trickiest part of the operation.
Matt's nerves work so fast and his touch is so precise
that he can make tiny adjustments without thinking.
He's acting on instinct'
depending on sensations working faster than we can think.
lt's something we all do every day.
lt lets us make music.
Create art.
And save lives.
MAN: Okay, swim mer and survivor are below the aircraft.
Hold. You're doing good. You're doing good.
MELOCH E: They risked their life to save mine,
and we all got out of there safe.
And if it wasn't for them, l wouldn't be alive right now.
NARRATOR: This forest of touch sensors
allows us to respond instantly
to whatever's happening around us.
But they're not evenly distributed beneath our skin.
Our hands have 1 00 times as many sensors per square inch
as the back of our legs.
They're placed where we need them most.
lf size went by sensitivity to touch,
our bodies would look something like this.
Tongues and lips, twice as big.
The same with hands, fingers, and feet.
Other senses have different patterns.
Sensors for heat are most dense in our fingertips, nose,
and, strangely, our elbows.
They play a critical role.
All over the human body,
every second of every day,
nerves carry sensations to our brains.
Even when we don't realize it'
these signals control how our bodies function.
When it gets hot'
sensors and nerves work together to keep us alive.
The deep Australian desert can reach 1 30 degrees.
lt's no place to get stranded,
but that's what happened to Matthew McGough
and his daughter' Shannon,
more than 1 00 miles from the nearest town.
lt's so hot here that a cut of beef left outdoors
would roast in less than four hours.
Yet Matthew and Shannon are still alive eight days later.
Moments after their pickup truck breaks down,
their bodies go into action
to hold their core temperature at about 98.6 degrees.
lt's all thanks to hundreds of thousands of tiny heat sensors
and the cooling system they trigger.
When our skin heats up beyond 93 degrees,
sensors signal our brain.
lts central thermostat uses other nerves
to start the cooling process.
One hour later' both of them are sweating profusely.
There's no more efficient way to cool the body.
Beneath our skin lie over a million tiny sweat glands.
When we heat up, our blood vessels dilate,
bringing blood and heat to the skin surface more quickly.
The sweat glands extract water from the blood
and release it into the open.
As it evaporates, it cools us.
Under ordinary conditions,
we produce about 2 pints of sweat a day.
But in extremes, we pump out a lot more.
This guy's churning out heat as he runs.
And what's more,
the room temperature is being increased at the same time.
The amount of sweat you're producing --
but more importantly, evaporating --
is just enabling you to release the amount of heat'
lose the amount of heat from the body
that you're producing through exercise.
We're seeing no increase now in the sweat production,
which suggests to us that you're sweating
at about your maximum rate.
NARRATOR: The man's near the sweat limit.
4 pints an hour.
But the water has to come from somewhere.
The human body is 75% water.
To survive, our vital organs need their share of that fluid.
Normally, we have enough to spare for the cooling system,
provided we keep the body filled up.
After four days in the Australian desert'
Matthew and Shannon have run out of water.
Losing as little as 3% of the body's water
can cause cramps, headaches, and disorientation.
They're so dehydrated, they start to hallucinate.
[ Water dripping ]
MATTH EW: The heat itself.
The heat plays tricks on your mind.
Trying to keep your mind on the job of surviving
and getting out of things and getting things done
and this, that' and everything else.
NARRATOR: Now their bodies must respond to the water loss.
To keep the body's vital organs supplied,
the brain fights back with a surprising response.
Overriding the body's thermostat'
the brain orders the sweating to stop.
The sweat glands drain dry.
Next' nerves signal other parts of the body
to suck water back into the heart' lungs, and kidneys.
The blood thickens and coagulates.
Water is absorbed from the large intestine,
causing constipation.
Even the eyes dry out.
MATTH EW: We had a good cry together
about whether we'd see Christmas or not
or whether Shannon would see her mom again
or whatever' you know?
And if we'd have had moisture in our body,
there would've been plenty of tears,
but there was none.
SHAN NON: l do remember how your mouth is all dry,
and you can't really swallow,
because there's nothing there to swallow with.
Your tongue is like having a brick in your mouth.
NARRATOR: Shannon and Matthew are near collapse.
But instead of cooking in the heat'
the network of sensors beneath their skin
has kept them alive for over a week.
They survived because their bodies balanced
the need for water and the need to keep cool.
Their brains even trigger one final instinct.
They just manage to dig in,
insulating their bodies from the searing desert.
lt's enough to save their lives.
[ vehicle approaches ]
MATTH EW: Just jumped up out of the ground
and started waving me hands frantically,
and he had lots of nice, cold rainwater on board, eh?
That was good. [ Laughs ] Yeah.
l grabbed this bloody great big jerrican full and upended it.
lt went straight through us, but' yeah, it was good.
lt was nice, cool, cold, clean rainwater.
lt was awesome, yeah.
NARRATOR: Our body's temperature responses
can be the difference between life and death.
Of all the sensations,
the one most of us would rather not feel is pain.
But pain is vital.
lts function is one of the greatest mysteries
of the human body,
and we're now beginning to unravel it.
Amy Racina is hiking alone in California's Sierra Nevada Range
when she stumbles.
She loses her footing.
Dropping 60 feet onto solid granite.
[ Crack ]
The fall fractures her right foot and shinbone.
Her right knee disintegrates, exploding into four pieces.
Her left leg shatters at the thigh and hip.
l nstantly, Amy's nervous system is on the case,
firing pain signals from ripped skin and wrecked bones.
Pain is there to protect us by alerting the brain to harm.
Any injury triggers chemical reactions within pain sensors.
They fire electrical signals into the nervous system
that travel to the brain.
Pain nerves work more slowly than others.
Signals that convey dull, throbbing pain operate so slowly
that we sense the delay between an injury happening
and the pain it triggers.
This delay gives us precious moments
to escape the cause of the pain
before the full effect overwhelms us.
l n the brain,
pain works differently from other sensations.
Other senses are processed in specific areas.
Sight.
Hearing.
Touch.
But if you could show pain, it would look something like this.
lt's processed in many different parts of the brain,
and the areas activated differ from one person to the next.
Pain's a perception. lt's in the brain.
lt's the brain's interpretation of an injury.
That's the reason why it's so different
among different people.
The analogy that l like to draw,
that maybe makes it a little clearer'
is two people looking at a painting.
One person says it's beautiful.
They're willing to spend $20 million to buy it.
The other person looks at it' doesn't get it'
and just walks right by.
The point is that pain
has an emotional component to the experience,
and it's the variation in the emotional component
that will color and alter the way a person perceives pain.
NARRATOR: So, we all feel pain differently.
lt depends on who we are and what we're doing.
[ Screams ]
[ Crack ]
NARRATOR: As she wakes up from her fall,
Amy Racina expects to be in agony.
But in extremes,
our nervous system can perform an amazing trick.
RAC l NA: l looked down at my legs.
There was a huge, gaping hole
where there used to be a right knee.
l couldn't so much as move either leg,
but surprisingly, there was no pain.
NARRATOR: The damage registers, but not the discomfort.
[ Crack ]
At impact' Amy's pain sensors start firing.
They don't run straight to the brain.
They go via the spinal cord.
As they enter the vertebrae, they pass through a gate.
Buried in tissue with the consistency of jelly
is the meeting of two nerves, known as a synapse.
Jumping a tiny gap,
the signal passes from nerve to nerve
and on up the spinal column toward the brain.
These junctions have a special property.
They can be turned off.
lt gives the brain amazing power.
To suppress pain,
the brain orders the release of endorphins.
They flow down to the junctions in the spinal cord,
where they smother the synapse,
stopping the pain signals from jumping across.
The result. No sense of pain.
These natural painkillers are stronger than morphine.
And whenever the pressure is on,
the brain can unleash their power.
BASBAUM: Soldiers who have been shot in the battlefield,
and they don't report im mediate pain
even though there's clearly a bullet wound.
There's bullets flying over their head.
Their life's in danger.
The brain is appraising the situation
and saying, "Now is not the time to experience pain."
NARRATOR: Amy's brain knew that feeling pain wouldn't help her.
Blocking it might give her precious time to act.
RAC l NA: The first thing that l did
was to treat the more obvious injuries.
The first danger was that l would simply bleed to death
from the open wound that was my right knee,
so l poured antibiotic ointment --
or actually, hydrogen peroxide --
on my knee and bandaged it up,
tying it as tightly as l dared,
'cause l had to stop the bleeding.
NARRATOR: Amy has fallen far from any help.
To have a hope of rescue,
she needs to get herself off the mountain
and closer to a trail.
But as she crawls, pain begins to creep in.
RAC l NA: l remember one time in particular
when l was working my way over and around a pool of water.
And l shifted my hip, and the pain was so bad,
l thought' " l'm going to pass out."
But my mind was still in control,
and l knew if l passed out at that point'
l would surely drown.
So, my mind remembers that there was quite a bit of pain,
but it never took control of my body.
NARRATOR: Battered, bleeding, Amy crawls for two days.
Throughout' she keeps her mind off the pain
thanks to the endorphins unleashed by her nervous system.
When rescuers do find her'
Amy relaxes, the endorphins stop,
and pain floods her body.
RAC l NA: The moment at which l truly felt the pain
was when l was loaded into the stretcher.
lt was absolutely excruciating.
lt was the kind of mind-numbing, screaming, horrible pain
where l had no ability to focus on anything but how bad it was.
[ Helicopter blades whirring ]
NARRATOR: Had she been feeling this way all along,
Amy never would have made it down the mountain.
But by blocking pain,
her nervous system helped her survive.
Eight operations later' Amy's walking again.
Her story is amazing, but it's not unique.
lf the situation demands,
anyone's nervous system can shut out pain.
But the body doesn't always try to neutralize pain.
Sometimes our nervous system makes us hurt more.
The sensation of pain
is often the only way we'll know that our body's damaged.
Pain serves as our central alarm system.
Working in an outbuilding on his farm,
David Edgar has no idea
that he's inches from one of America's deadliest spiders,
the brown recluse.
These tiny spiders attack humans only rarely.
But today David is unlucky.
At first' he doesn't notice the bite.
A day later' though, he begins to feel pain.
l woke up in the morning,
got out of bed, put my jeans on,
and l just felt something on my leg.
lt was kind of burning, kind of hurting.
And l got to looking.
On the back of my leg is a big old red spot
with a little black spot in the center of it'
and, boy, it hurt.
Over the weekend, l was miserable. l couldn't sleep.
lt was just constant' burning pain.
NARRATOR: But David's pain wasn't from the spider bite.
lt was his body working to save his life.
Whenever our skin is broken,
whether it's a spider bite or just a simple cut'
the body fights back quickly.
First' it sends enforcer patrols of white blood cells
to clean the wound.
Then the surrounding tissue swells,
irritating nerve endings.
The area becomes inflamed and painful.
Here, the injury itself has not created the pain.
lt's the body's reaction to it.
And it happens for a good reason.
The pain of inflam mation
is another way our nervous system defends us.
lt's a safety perimeter'
the bodily version of the tape police officers put up
after an accident.
The tape warns drivers to stay clear.
The pain we get from inflam mation
warns us to protect the area or do something about it.
And if you ignore a brown recluse's spider bite,
the result can be a nasty surprise.
An ugly, ulcerated wound, even gangrene.
For David Edgar' his nervous system's response
warned him about the bite just in time to get treatment.
Whether it's the im mediate pain of broken bones
or the delayed pain of inflam mation,
it's there for the same reason.
To protect the human body.
Pain is one of the most fundamental,
primal experiences that we have.
Without pain, we wouldn't survive as a human species.
lt's so bad because it's so good.
NARRATOR: The surprise is that pain sensors
are working for us all the time without us knowing.
They make us shift in our chairs while sitting.
Toss and turn at night.
They're why, when walking,
we instinctively land on different parts of our feet.
Subtle pain signals constantly alert the body
to make adjustments.
Otherwise, we'd stress bones and blister skin.
Pain can be terrible,
but living without the sensation is even worse.
Tell me if you feel that vibrating.
F eel it?
Honestly, no.
NARRATOR: Carol Saks is one of 2 1 million Americans
with diabetes,
a disease that leaves too much sugar in the blood.
What about here? F eel it here?
Barely.
NARRATOR: Excess blood sugar can damage nerves,
leaving parts of the body
unable to sense touch, temperature, or discomfort.
Nothing, no.
NARRATOR: lf you can't see an injury or feel it'
you won't know you need to treat it.
Your sensation isn't good.
What you need to do is always check your feet.
NARRATOR: Anyone without nerves
to transmit the sensation of pain
must be extra careful.
The smallest wound could become infected,
with inflam mation spiraling out of control
before the patient realizes it.
The nervous system is essential to who we are.
Without sensations like pain,
our bodies would soon fall apart.
But this mass of wiring works in mysterious ways.
Sensations tell us about the world around us.
But under certain circumstances,
it can work the other way around.
Our nerves tell the world about what's going on inside us.
lt might be the cheeks flushing with embarrassment
or a voice choking with emotion.
Our physical reactions can reveal what we truly feel.
And some think they can show when someone's lying.
TRl MARCO: Typically, when a person tells a lie,
they begin to sweat.
l'm sure we've all seen
the 1 940s and,50s interrogation movies
where the person in the hot seat has a sweaty brow
or a sweaty upper lip
or perhaps sweat dripping down from their sideburns.
lf you'll lean forward, put your arms out
like you're gonna dive into a swim ming pool.
This will go around your stomach.
NARRATOR: Jack Trimarco uses physical sensations
to probe for truth.
His primary tool. The lie detector' or polygraph.
TRl MARCO: This cuff is just like the one that the doctor...
Polygraph works very similar
to any other biofeedback instrument.
lt simply records deviations
from a person's physiological norm,
such as someone's blood pressure
going up and then coming back down
or perhaps a decrease or an increase
in pulse rate or sweat-gland activity.
Are you sometimes known as Bobby?
Yes.
NARRATOR: A polygraph examiner
knows what to look for when questioning someone.
Do you intend to be completely truthful with me?
Yes.
NARRATOR: Any deviation from normal could signal deception.
Our body can give us away.
And are you sure that l won't try to trick you on this test?
Yes.
NARRATOR: We may think we're being cool,
but when we're stressed,
our network of nerves starts to prepare our body for action,
as if it's under attack.
lt's a response that harks back to our ancient ancestors.
Fight or flight.
No.
NARRATOR: lt starts by triggering your stress hormone,
adrenaline.
Your heart rate increases to pump more blood to your muscles,
as if you were about to go into battle.
Your breathing deepens
as vital oxygen reaches your muscles.
And you begin to sweat.
The body cools so that you won't overheat
when rushed into action.
The brain won't let us stop this survival strategy.
These basic nervous functions are automatic.
That's why a polygraph can often uncover a liar.
But some nervous functions we can control,
and that opens up possibilities
which could help revolutionize medicine.
How are you doing, Steve?
NARRATOR: Ashley Goodman isn't your everyday dentist.
He uses hypnosis to control pain.
Now, what l'm gonna want you to do
is be able to form a mental picture.
NARRATOR: Today, he'll be drilling out a tooth
to replace a crown with no anesthetic or drugs whatsoever.
Oh, it's so comfortable.
DR. GOODMAN: Pain is perception.
Reality is perception.
So, what we can do is alter their perception of reality.
Deeper.
NARRATOR: As the hypnosis begins,
Dr. Goodman completely changes
Steve Fines' perception of his world.
l want you to notice wave upon wave of relaxation
with each breath you take,
letting out the breath, the tensions of the day,
down still deeper.
The most comfortable, secure...
NARRATOR: For Steve, things are about to get very weird.
l n only minutes,
Steve has stopped thinking he's in a dentist's chair.
lt isn't necessary for your mind to stay here.
Your body will need to stay here and be treated,
but your mind can go wherever you'd like.
NARRATOR: Hypnosis transports him to an imaginary playroom
full of toys and gadgets.
Down deeper.
NARRATOR: When the drilling begins,
Steve thinks it's toys buzzing.
What l'd like you to do now is just open your mouth.
And in the background,
you will hear noises of the electronic toys.
[ Drill whirring ]
There's some of the toys now.
NARRATOR: Everything you're now seeing is for real.
Normally,
no one could endure such treatment without feeling pain,
but Steve has been feeling something completely different.
[ Whirring continues ]
The theory is that hypnosis
acts on the brain's emotional response to discomfort.
Brain activity can change temporarily,
so we process pain signals as if they were a different emotion.
As the tooth enamel shatters,
pain sensors are sending signals along the nerves.
But inside Steve's brain,
messages that would normally be received as pain
have now become pleasant sensations.
After 45 minutes,
Dr. Goodman brings his patient out of hypnosis.
DR. GOODMAN: At the count of three,
awaken refreshed and alert.
1...2...3.
-How did you feel? -Fine.
Good. We're all finished.
F abulous.
NARRATOR: The hypnosis is a success.
lt completely fools Steve's nervous system.
l remember laying back in the chair
and then just kind of feeling some slight sensation.
And other than that' everything was fine.
Just nice, very relaxed feeling.
NARRATOR: The effect lingers.
Steve's mind will continue
to interpret the pain as pleasurable
until the tooth heals.
Usually, we can't control the sensations
that link our bodies with the outside world,
but science may be about to change that.
[ Neighing ]
Nine years ago while shooting a com mercial,
Laura Tibitts fell from a horse.
She recovered,
but she still suffers from chronic pain in her shoulder.
l've had two surgeries, done tons of physical therapy.
l've tried acupuncture, done massage therapy.
lt becomes a full-time job, just trying to manage your pain,
when all you really want to do
is move on and go back to your life.
NARRATOR: Laura is still looking for ways
to overcome pain that never goes away.
Now she may be able to take control of her own sensation.
The Shaolin monks of China
are famous for fighting skills and acrobatics,
but above all for their ability to somehow manage their senses.
[ Applause ]
Does this really not hurt' or do they just not mind the pain?
To prepare themselves for their grueling acts,
the monks use one of the oldest forms of pain control.
Meditation.
[ Jialin speaking native language ]
l NTERPRETER: You have to focus 1 00%.
We need willpower to channel our chi, our spiritual energy.
When we meditate,
we channel this spiritual energy throughout our body.
NARRATOR: Meditation starts by changing how the body works.
The heart slows, pumping less blood.
The muscles relax.
Relaxed muscles means less tension, which means less pain.
But the strangest effect occurs in the brain.
Astonishingly, although the brain is still alert'
meditation lessens the emotional reaction to pain.
lt's like turning down the volume,
so when pain sensations hit' they have little effect.
[ Applause ]
That's how the monks can tolerate
what for anyone else would be extraordinary pain.
Now technology could help Laura achieve these same results
as she thinks away her pain.
An advanced MRl scanner
shows what sensations look like deep within the brain.
Because pain activity occurs all around the brain,
it's hard to know where to look.
But pain creates strong emotions
that offer a map of this mystifying sensation.
MACKEY: These pictures don't show pain.
That's an important distinction to make.
Much like any study that we show
where neural imaging of love or fear or hate,
we're not actually showing those experiences in the brain.
What we're doing is, we're showing the brain regions
that play a role in that experience of pain.
NARRATOR: Perhaps by watching for activity in this region,
we can find a way to control the sensation of pain.
Laura watches her brain working in real time
as the scanner charts the emotional activity
that her pain causes.
MACKEY: We can focus on a specific region of the brain,
and we can process that brain activity level
and send that back to them
so that they can see their own brain activity in real time,
much like a fighter pilot would see a cockpit display.
NARRATOR: Brain scans are hard to read,
so they represent the activity in the form of a flame.
The bigger the flame, the more activity in this crucial area.
Laura's job is to shrink the flame using only her mind.
MACKEY: Okay, Laura' we're now gonna move on
to getting the brain imaging scans
and having you focus on decreasing your pain.
NARRATOR: As if she were isolating a muscle at a gym,
Laura uses the flame
to target the appropriate part of her brain.
To think the pain away,
Laura has devised ingenious mental exercises.
Tl B lTTS: To get the pain down,
l would sometimes resort to stopping
and thinking just what on my body doesn't hurt
and then focus in on that location of my body
and try to really clear my mind.
l also would imagine little people coming and marching
and taking the pain and scooping it out'
literally removing it.
NARRATOR: The results are astonishing.
Patients trying this method
say their pain has shrunk by nearly half on average.
That's about as much as many pain drugs achieve.
MACKEY: People can learn
how to control a specific region of their brain
if they see it on a moment-by-moment basis,
and that was what was exciting about this.
And that' for the first time, we showed that people
can actually tap into a specific region of their brain
and learn to control it'
and it leads to a specific change in behavior'
'cause that's never been done before.
NARRATOR: Someday this technique might also help treat illnesses
such as depression or addiction.
lf it works,
we may all be able to take as much control of our sensations
as the Shaolin monks.
The human body is quite literally a bundle of nerves.
They transmit sensations that keep our bodies in harmony.
They give us pleasure and alert us with pain,
always at the ready to trigger our bodies into action.
We're still learning the true potential of our senses.
The further we can push their limits,
the greater the superhero within all of us.
The human body.