Original subtitles

Freeman: It is a nightmare that has stalked us for centuries.

Hordes of human beings transformed

into mindless, bloodthirsty monsters,

and civilization collapses. [ Siren wailing ]

Could this nightmare become reality?

Scientists have discovered parasites that turn the living

into the walking dead,

and new strains of deadly pathogens attack us every year.

Neuroscientists are learning how to take over our minds.

Will we someday lose control of our bodies and souls?

Is a zombie apocalypse possible?

Space, time, life itself...

The secrets of the cosmos lie through the wormhole.

Through the Wormhole 05x06 Is a Zombie Apocalypse Possible? Original Air Date on J

== sync, corrected by elderman == @elder_man

According to Haitian folklore,

certain priests had magical powders...

[ Thunderclap ] That could transform a corpse...

into a puppet.

Our popular culture has turned that zombie legend

into an apocalyptic nightmare,

a contagious virus that turns the infected

into violent monsters with rotting flesh.

[ Thunderclap ]

We are all just one bite away

from joining the mindless legions of walking dead.

All of these are myths, of course.

[ Thunderclap ]

But every myth has a grain of truth.

Could our imaginations

be telling us something about our future?

[ Thunderclap ]

Freeman: A long time ago,

my friends and I saw a movie... [ Door creaks ]

that gave us nightmares... [ All gasp ]

"The Mummy."

[ Children screaming ] In that story,

ancient magic made a corpse walk the earth again.

Could such a mindless monster ever exist in the real world?

David Hughes is an entomologist.

He has a long history

with the dark side of that science.

When I was a kid

I had a rather personal relationship with a fungus.

We didn't know exactly what it was at the beginning,

and over the course of months,

this fungus creeped its way across my scalp,

uh, making me half bald.

Freeman: David survived,

but his fungus was not the worst nature has cooked up.

Some funguses turned the bodies of their hosts into piles of rot

and enslave their minds.

David is the foremost expert on a fungus

that turns its victims into the walking dead,

or to be more accurate, the crawling dead.

The fungus, like all organisms on the planet,

has a scientific name.

This one's called ophiocordyceps unitlateralis.

But colloquially, it's known as the zombie ant fungi.

Freeman: While foraging for food,

an unsuspecting ant

will pick up a spore of the zombie fungus.

The fungus bores through the ant's body.

It multiplies and infects the ant's brain,

where it releases

powerful mind-controlling chemicals.

The zombified ant bites the underside of a leaf

and dies.

Well, sort of.

Death is really the starting point for the parasite.

Fungi are rather interesting

in that they require the host to die,

and then, from its tissues, they grow and they reproduce.

And so, at this stage,

the whole ant body is completely transformed.

Freeman: The zombie ant fungus continues to control

the dead creature's mind,

keeping the insect's jaw locked onto the leaf.

The fungus multiplies,

building pressure inside the ant's skull

until...it breaks open.

Out comes a fungal stock that sprays down deadly spores

on the fungus's next victims.

The cycle repeats.

The fungal spores need to be shot out, launched,

from an area high above the foraging trail.

And so the fungus has evolved the ability

to control the mind of its host.

Freeman: Inside their nests, ants are hygienic.

But when they're out foraging,

they are vulnerable to infection.

David believes the fungus evolved the ability

to strike the ants during this moment of weakness.

The zombie ant fungus could never infect us.

Our brains are too different from those of ants.

But could a similar pathogen ever find its way into our mind?

So fungi have clearly evolved the ability

to control the behavior of animals.

Our brains are animal brains, and there's no reason,

theoretically, why we couldn't have our behavior controlled.

Freeman: If a mind-enslaving pathogen ever strikes humanity,

it will most likely jump to us

from our close genetic relatives.

Microbiologist Kartik Chandran studies the Ebola virus...

A pathogen from our worst nightmares.

Within weeks of infection,

most patients leak blood from every orifice and die.

Kartik is leading a team to find out

how deadly viruses like Ebola evolve to infect humans.

As far as we know, Ebola lives in bats,

and every once in a while,

this virus can break out from bats into other animals,

including primates and apes and humans.

Freeman: Kartik is investigating

how Ebola made the jump from bats to us.

He's imagining what it's like

to be one of the microscopic bad guys.

[ Static, door creaks ]

The human body is a lot like a building

where our cells are rooms.

Viruses infect us by breaking and entering.

So you might ask me, why does this little room

in this storage facility have a lock?

And so the answer is obvious --

because somebody needs to go in and out.

This is an attempt to secure the entrance

so that only the authorized individuals can get in.

And cells are the same way.

You know, cells need to bring stuff in,

they need to export stuff,

and viruses have really evolved to exploit

this sort of entry and access ways.

Freeman: Viruses mimic the shape of nutrients

that the cell needs to survive,

just like a lockpick mimics the shape of a key.

[ Click, door rattling ]

Freeman: Once inside the cell,

the virus inserts its malicious genetic code.

The host cell becomes an enslaved factory,

producing countless copies of the invader.

[ Screeching sound ]

A multiplying virus can build so much pressure

inside the host cell that it explodes...

[ Explosion ]

...ejecting millions of viral clones to infect other cells.

For a virus to jump from animal to human,

it has to find a piece of biological machinery

shared by both the animal and the human cell.

Like you often see with viruses and other parasites,

they evolve to co-opt these common cellular mechanisms,

and Ebola has done just that.

Freeman: Kartik made a groundbreaking discovery.

Ebola relies on a protein called npc1 to infect cells.

NPC1 is found in both bat and human cells.

[ Chirping ]

Bats and humans may seem very different,

but their cells use remarkably similar molecular machinery.

Most viruses that infect bats can also jump to humans.

All a virus has to do is find those common keys.

So, I mean, I think it's a probability thing.

The more closely related you are to another organism,

the more likely you are to pick up a virus.

Freeman: A virus that turns human beings

into violent, unconscious monsters already exists...

Rabies.

People that have rabies

go through a phase where they're highly violent and belligerent,

and they can foam at the mouth.

These are changes that are --

clearly seem to benefit the virus

in terms of its ability to spread

from one infected host to a naive host.

Freeman: A rabies infection

does not spread easily from person to person.

But if a virus like rabies mutated

to have influenza-like properties,

it could spread like wildfire.

[ Coughing ]

Freeman: The infected would mistake it for a common cold...

...until it's too late...

[ Coughing ]

Freeman: ...and they fall into a mindless rage.

They would become violent and attack without warning.

[ Strangled yell ]

[ Stabbing sound ]

[ Panting ]

[ Gasps ] [ Banging on door ]

Freeman: Open wounds would benefit the virus.

It would easily transmit through airborne particles.

[ Elevator bell dings ]

Ironically, our own vigilant immune systems

could help bring this virus into existence.

Once a virus infects a cell,

there is sort of this hardwired immune response

that makes all these new machines in the cell

that can try to stop the virus from infecting,

and so the virus has got to evolve

so it can get around these sort of antiviral proteins.

Freeman: In the never-ending arms race

between the virus and the host's immune system,

both sides keep upping their game.

As viruses mutate, they develop an array of evasive talents.

In some mutations, viruses learn to become invisible.

[ Switch clicks ]

Other times, they evolve chemical tools

that allow them to disable the body's infection monitors.

[ Static ]

Or if the virus mutates just right,

it can permanently evade the immune system with a decoy.

Eventually, a new form of the virus will evolve

that can slip past the body's defenses.

And that virus is selected because it's the only one

that's able to grow and replicate itself

in these cells, and so, all of a sudden,

it takes over the whole population.

So you go through these sort of, like, bursts of selection

that completely change the --

sort of the structure of the viral population.

And this can happen very quickly.

Freeman: As long as we rely on our immune systems

to keep us healthy, new viruses will constantly evolve.

But a zombie virus may also

one day be created in a laboratory.

We should be able to design viruses

that do different things.

In principle, it seems to me

that if you know what buttons to push,

you could make a virus that could do those things.

Freeman: Kartik, of course,

wants to stop a zombie virus, not create one.

But nothing is preventing the wrong minds

from pursuing it.

Is a zombie virus possible?

I mean, I suppose there's really nothing in the laws of physics

that says it's impossible,

although I would say that it could be

some sort of combination

of different viruses that we know about.

Freeman: A hybrid virus that turns human beings

into deadly, contagious monsters is not likely,

but it is possible.

It could come from a laboratory,

or could be born from the crucible of evolution.

If this virus breaks out, what happens next?

When you get the flu, what do you do?

Go home, get in bed, and hope no one bothers you.

But imagine a disease that spreads

by making its victims violent.

Such a disease could emerge someday.

Could we keep it from becoming a global pandemic?

In Ottawa, Canada,

a scientist is taking on the zombie apocalypse

before it happens.

[ Beeps ]

A scientist who always seems to have a question on his mind.

I added the question mark because my name was very boring,

and I was getting confused with all kinds of Robert Smiths,

so I thought it'd be a cool thing to add to my name.

And because I have my question mark which helps me

be distinguished from other Robert Smiths

in my specific field of disease modeling by mathematics.

Freeman: Diseases are everywhere.

[ Coughs ] Robert wants to log

every moment in his life... [ Cell phone rings, beeps ]

When he can pick up a pathogen from an infected person,

even when the infected aren't around.

[ Water streaming ] If a disease is airborne,

then the air that we share

is obviously something that's potentially quite toxic.

[ Cell phone rings, beeps ] And the closer you are,

of course, the more likely.

But then other things become transmissible as well.

So doorknobs and, you know... [ Cell phone rings ]

[ Beep ] The handle of whatever it is

that I'm touching or breathing on.

[ Cell phone rings ]

[ Beeping ]

Freeman: Robert is using this data

to build mathematical models to predict

how quickly infectious diseases can spread.

And with the help of his students,

he's creating live human versions of those models.

Just like any human community,

the virus has many chances to find a new host.

Okay, in these beakers, most of them are just plain water.

One of them has been infected

with something that's gonna simulate a virus.

Freeman: The rules are simple.

No student can take more than five steps.

Ready? And go. [ Blows whistle ]

Freeman: They have 30 seconds to mix

with as many other students as possible,

and no one knows who has the beaker

with the infection.

Robert wants to see how many people patient zero can infect.

[ Toot ]

Okay, now please return your beakers to the middle.

Freeman: At the end of the game,

Robert drops a chemical into each beaker.

If a student mixed with the infected,

their water will turn yellow.

Even though patient zero

could only have direct contact with a few neighbors,

those neighbors passed the disease along,

and about half the group ends up infected.

But Robert believes the math desperately needs an update.

So recently, we tried to update models,

and we have much more powerful ways of understanding

the network of connections that different people have.

[ Film projector whirring ]

Freeman: The old models focused on human beings

and their local communities.

But we now live in a global society

and are on the move like never before.

On an average day, approximately 22.8 million of us

travel someplace far away.

Robert repeats the game with the same rules,

but this time, the students are allowed

to take as many steps as they wish

to account for the ease with which we travel.

[ Toot ]

[ Toot ]

Freeman: At the end of the 30-second round,

Robert tests each beaker again.

Every student is infected.

Robert has calculated

the infection rate for a disease that doesn't yet exist.

He imagines a virus that spreads easily through the air,

like the flu.

But unlike influenza,

the disease does not make its victims

want to stay home in bed.

Instead, they become zombies,

and they take to the streets in a mindless rage.

[ Snarls ]

So if we actually had a zombie virus,

then the mathematics predicts

that we're not gonna do very well.

[ Sirens wailing ]

Freeman: If just one person is infected with this zombie virus,

Robert predicts an epidemic is inevitable.

Cities would be overrun in weeks.

[ Crowd shouting indistinctly ]

Freeman: As refugees escape,

some of them inadvertently bring the disease along.

Global civilization as we know it

would be brought to its knees in a matter of months.

We have completely eradicated only two infectious diseases --

cattle plague and smallpox.

Finding a cure for this hypothetical zombie virus

is very unlikely.

But if a zombie outbreak does happen,

Robert's calculations

show how humans can avoid total annihilation...

by getting our hands dirty.

Probably the best way that we found to deal with zombies

was to basically hit them hard and hit them often.

So the idea is that you try and wipe the zombies out in one go,

and of course, you're not gonna be successful at that,

so, next day, you try and wipe them out again,

using the knowledge that you learned from the last time.

So we get better at it,

and so then the third day, we're now even better.

Freeman: To stop a zombie plague from becoming an apocalypse,

we may only have one horrifying option --

to kill every single infected person.

Just one surviving zombie could trigger another epidemic.

Our best hope to stop a super virus

is to catch it in time.

Virus hunters are scouring the microscopic world,

looking for an invisible enemy

that may have already made its first move.

During the four years of World War I,

almost 15 million people died.

In the two years that followed,

a single flu virus claimed three times that many lives.

The virus had spread around the world

before anyone detected it.

There are millions of microbes out there,

most of them harmless.

How can we find the next deadly pandemic,

perhaps a zombie virus...

[ Imitates gunshot ]

...before it sweeps the globe?

[ Blows air ]

[ Wind blowing loudly ]

Hello?

Hello?

Freeman: According to Ian Lipkin,

the world's leading virus hunter,

our civilization runs a terrible risk of global pandemic.

I'm standing in the middle of Times Square,

and it's completely deserted.

It looks like something that you might see in a movie,

but, in fact, it's a real possibility.

Freeman: Ian is the director

for the Center for Infection and Immunity

at Columbia University.

His team is on the front lines,

hunting for deadly viruses before they become pandemics.

In 2003, his lab was the first

to identify the lethal S.A.R.S. virus.

That early discovery saved countless lives.

Nature herself is continually evolving new bacteria,

new viruses that are more pathogenic,

that escape the antivirals, the antibacterials,

the vaccines that we create to hold them in check.

[ Coughs ]

Freeman: There are more

than 10,000 trillion trillion trillion viruses on earth.

Pinpointing a deadly virus in a sea of its benign cousins

is just about impossible,

unless you lure the virus out of hiding.

When a patient falls ill somewhere in the world

with an unknown virus,

blood and other biological samples

are often sent to Ian's lab.

He then gets to work by going fishing with D.N.A.

D.N.A. makes for the perfect virus bait,

because viruses contain genetic code

that binds to matching sequences of D.N.A.

So then if that virus is present within that sample,

it will be caught on the hook,

and I'll be able to reel it in, and I'll see it.

Freeman: Ian can cast thousands of genetic lures

into the sample.

Each one is tailored to attract a known virus.

[ Screeches ]

Freeman: Biological samples from sick patients

are oceans filled with microbes that ignore the lure,

except for the virus that is a match

for the lure's D.N.A. sequence.

The virus lines up its genetic code --

A binds to T, C binds to G.

Once it's hooked... Uh-oh.

The weight of the lure changes,

and Ian can reel in the virus.

[ Seagulls crying ]

[ Click ]

Now, if that method works, then we can get an answer

very, very quickly, very inexpensively,

probably in a matter of four to six hours at the outside.

Freeman: But viral and genetic code

can evolve rapidly.

Sometimes new viruses have changed so much

that they no longer stick to the lure.

In that case, Ian switches to another technique --

grab all the D.N.A. he can.

I have a net.

This is essentially a D.N.A. sequence.

When we don't know precisely what we're looking for,

we use a high-throughput sequencer

that allows us to characterize all of the genetic material

that'd be present within a sample.

We pull everything in, and then we compare that

with a database of all known sequences.

That allows us to identify anything

which is potentially a microbial agent.

Freeman: Ian and his team

then grow colonies of the isolated virus

and attempt either to identify a drug

that can fight the infection or to develop a vaccine.

We and our colleagues can begin testing drugs for efficacy,

drugs that will be able to prevent this agent

from reproducing itself.

And then, ultimately,

because drugs are frequently too expensive,

we try to collaborate with people

who know how to develop vaccines.

Freeman: No matter how quickly

they identify new viruses, however,

there will always be a lag time between detection and treatment,

a time when the virus can spread.

The major time lag is not at the level of the laboratory.

It's really in the field.

It's recognizing the appearance of something as new.

Then that has to percolate

through the ether until it reaches people like us.

Freeman: Ian's team could prevent

millions if not billions of us

from succumbing to a highly infectious disease.

But if a virus evolves that is sufficiently different

from the viruses we know today,

Ian's team will not be able to fish it out.

[ Beeping ]

In humanity's war on viruses, we need a new strategy.

We can hunt viruses down,

and we can try to vaccinate ourselves against them.

But once they infect us, we're at their mercy.

What if we turn a virus into a zombie

that works for us and make it kill a zombie virus?

Modern medicine

has conquered many diseases in the past century.

Viruses, however, remain elusive targets.

Because they hijack the vital genetic machinery of our cells,

killing them is tricky.

The solution may require a pair of these,

shrunk down to the size of our D.N.A.

[ Snip ]

Viruses are party crashers.

They do everything possible to blend in with healthy cells...

Aah! [ Snarling ]

Freeman: ...All the while

relentlessly infecting the invited guests.

For severe infections,

our best medical treatments today are crude.

They work by chopping up the harmful invaders...

Party's over.

[ Motor revs, women scream ]

[ Saw buzzing ] ...And all the healthy cells

in their vicinity.

But a new treatment that only goes after the bad guys

could be right around the corner.

As the director of the Center for Nanomedicine

at U.C. Santa Barbara,

Jamey Marth thinks it should be possible

to make an antiviral drug

out of a class of chemicals that we all have in our stomachs.

The food that I have on this plate right now

is what I need to keep me alive and mostly healthy.

[ Crunching ]

But for my body to use this material,

it has to convert it into different forms,

and it does that by using small natural machines called enzymes.

Freeman: Enzymes are the power tools of microbiology.

In the stomach, they break apart our food into digestible forms.

Jamey and his colleagues are working

with an enzyme called C.R.E. Recombinase.

This enzyme has remarkable utility.

It can cut out any section of D.N.A.

And neatly staple back together

the two adjoining genetic pieces.

It's allowed us to do things

that we haven't been able to do before --

to remove specific genes from specific cells

at different times.

Freeman: Inside every cell in our body,

there is a forest of D.N.A.

Viruses sneak foreign genes

into this forest and hijack our cellular machinery.

A drug based on Jamey's C.R.E. Recombinase enzyme

could chop down viral infections at their root

by weeding out their D.N.A.

The enzyme needs to find a specific sequence

of 34 genetic letters at either end of the cut.

And that sequence can be customized.

So once you know the genetic sequence of a virus,

you can program C.R.E. Recombinase

to latch onto the first and last parts of this D.N.A. code.

This represents viral D.N.A. --

D.N.A. that's foreign to the cell

and has integrated itself into the genome.

An enzyme like the C.R.E. Recombinase

is capable of removing this precisely

from the cell's genome.

It does this with precision.

[ Snip ]

And then, what the enzyme will do

is it will stitch back together

the ends of the normal D.N.A.

So that the cell is effectively cured...

[ Stapler clicks ]

...of the disease.

Freeman: Jamey is laying the groundwork

for what could be a cure for all infectious viruses.

H.I.V. A.I.D.S...

[ Snip, click ]

...influenza...

[ Snip, click ]

...even the common cold...

[ Snip, click ]

...will all only exist in history books.

And the delivery vehicle for this life-saving drug

is the last thing you would expect --

another virus.

We could reprogram that virus so that once that virus

binds and goes inside the cell,

instead of releasing a disease-causing payload,

it will instead release a cargo

that allows us to cure those cells.

[ Screaming and crying ]

Freeman: Our best weapon against a virus

that turns humans into zombies

could be a virus that we turn into our zombie slave.

[ Roars ]

Freeman: This harmful virus

would be stripped of its disease payload

and instead be filled

with reprogrammed C.R.E. Recombinase enzymes,

which can search throughout our entire bodies

and only eliminate the unwanted invaders.

[ Clinking ]

But finding a universal cure for viruses may not save us

from a world filled with zombies.

A zombie takeover is already underway in a lab

in North Carolina, where living creatures

are turned into zombie drones at the press of a button.

If I told you to run off a cliff,

you wouldn't do it, would you?

But what if I took control of the neurons in your brain

and made your legs run straight off the edge?

Turning a conscious person into a mindless zombie

may only be a matter of finding

and controlling the right circuits in the brain.

[ Electricity crackling ]

[ Chuckles ]

How do you get a living mind to completely surrender its will?

Electrical engineer Alper Bozkurt

thinks we've been doing it for centuries

by domesticating wild animals.

The horses open themselves to our control

thanks to this mutual beneficial relation that we have with them,

and it took a long time for us to be able to train them,

uh, basically to condition them

with different rewards or punishments.

Freeman: Alper looks at animals as electrical circuits.

As a horse moves,

its brain sends

an elaborate series of commands to its muscles

through the electrical wiring of its nerve cells.

[ Electricity crackling ]

But convincing a horse to make these complex movements

only requires a simple input.

So when the rider wants the horse to go to left,

she just pulls the reins to left...

[ Nickers ]

...and the horse starts going in that direction.

And then, she wants it to go right.

She just pulls it to right,

and we see that horse is going on the right.

[ Nickering ]

And then she wants it to go forward.

She just provides a gentle kick with her heels,

and the horse knows that it needs to go forward,

and it does it.

[ Blusters ]

Freeman: The horse obeys because of its training.

But Alper thinks he can get

the same results in other creatures

without conditioning by replacing mechanical commands

with electrical signals sent directly to the brain.

I have a set of domino stones here

representing a neural network like in any brain.

A brain is a set of electrical relay networks.

It is composed of excitable cells called neurons.

Freeman: When neurons become electrically excited,

they pass a signal on to their neighbors,

which in turn pass the signal along.

Alper only needs to stimulate one neuron,

and the entire neural circuit will activate,

resulting in a complex bodily action.

It's a principle that should work in any brain,

but Alper is starting with a simple mind --

the cockroach.

Alper implanted electrodes into the sockets

where a roach's antennae connect to its brain.

[ Clicking ]

When he sends an electronic pulse to the neurons inside,

the roach becomes...

a zombie.

It goes wherever the electronic pulse

tells it to go, and it even turns on a dime.

So when we stimulate the right antenna of the insect,

insect thinks there there's an obstacle in front of it,

and it tries to make a left turn.

And when we stimulate the left antenna,

it tries to make a right turn.

Freeman: Alper thinks his zombie bugs

will one day save lives.

He envisions cockroach cyborgs outfitted with cameras

and G.P.S. chips

so they can locate survivors under collapsed buildings.

But his breakthrough could be the beginning of a world

where no mind is safe.

Theoretically, even a human could be zombified.

We know how neurons work,

and, uh, we can communicate with them.

When we stimulate the insect,

it is the same stimulation principle

that is used in deep brain stimulation patients

with Parkinson's disease.

So these are all the same principles.

It's relatively easy with cockroaches

to make them follow our command signals.

But with higher organisms, with vertebrates,

it is much complicated, although it's not impossible.

Freeman: Technology may soon exist that, in the wrong hands,

could turn us into zombies.

If our minds are taken over, will we even know it?

A zombie apocalypse may already be happening today.

In fact, this neuroscientist thinks

we're already 98% zombie.

In fiction,

the nightmare of a zombie apocalypse

is constantly taking on new forms,

but they all have a common theme --

the infected don't even know they are zombies.

If, right now, we were zombies in the midst of an apocalypse,

would we even know it?

[ Birds chirping ]

Neuroscientist Scott Grafton

believes that in sports like golf,

it pays to be a zombie.

I was watching this tournament

where Fuzzy Zoeller was winning.

[ Whack ]

Announcer runs up to him and says,

"Fuzzy, how did you do it? How did you win?"

He says, "Well, I've been brain-dead all week."

[ Whack ]

Freeman: After enough practice, a good swing is automatic.

In fact, nearly everything that our bodies do

requires little, if any, thought.

Almost all of our actions are actually unconscious.

We can pretend we access our muscle.

You know, when I hold a golf club,

I can grip it, and then I can think,

okay, flex this muscle, extend this muscle,

turn my shoulders, turn my waist, so forth.

But actually, I have very, very poor access to those muscles.

It's much easier to visualize what you'd like to happen,

and the swing just takes care of itself.

[ Whack ]

Freeman: Our brains are goal-oriented.

We think of an end result,

and our bodies mindlessly follow a program to achieve it.

Freeman: For Scott, this is evidence

that our willpower is not as strong as we think.

On a good day, I think we're about, uh...97% zombie,

and on a bad day, 98% zombie, and the rest of the 2 or 3%

is us having actually willful control

over our daily activities.

Freeman: Scott is running an experiment

to momentarily rob his subject, misty, of the other 2%.

He uses a technique

called transcranial magnetic stimulation,

or T.M.S., to induce

a harmless electrical current in her brain.

[ Click ] Oh.

T.M.S. is a method for

very briefly turning off a small part of your brain,

so it's a copper coil that goes against the skull,

and you induce a current through that,

and during that time,

you essentially have a virtual lesion in your brain.

[ Clicking ]

Freeman: Scott calibrates the device

by stimulating the neurons that control her right hand.

He then moves the device to focus on her parietal cortex.

This region of the brain is believed to be responsible

for making sure that our actions match our intentions,

like trying to touch an illuminated dot.

In the first round of Scott's experiment,

there is no T.M.S. pulse.

As soon as their hand starts moving,

we jump that second light to the right a few inches,

and their hand quickly corrects for that jump,

and it smoothly goes over and pursues that new location.

Freeman: But in the second round,

right as misty's finger moves, Scott zaps her parietal cortex.

Oh.

Freeman: She doesn't feel the pulse

but loses the ability to consciously

correct her action for a brief moment.

They react, essentially,

as a zombie and go to the original location,

that second light,

and they're unable to correct themselves on the fly.

So when we turn off the parietal lobe,

we're essentially making a person a full zombie

for just a second or so.

And during that time,

they're just carrying out a movement

that they no longer can control.

Freeman: Scott believes we evolved to be 98% zombie

so that the intellectual parts of our brains

could be freed up from thinking about the menial tasks

that take up most of our time.

For all of its evolutionary advantages,

the intelligent human brain may come with a cost.

I think we're a hair's breadth away from a zombie apocalypse

in the sense that most of what we do,

we can accomplish without thinking about it.

Just think about how many willful choices

you've made in the last week.

It's probably maybe one or two.

Everything else you did was essentially automatic behavior.

So now you think of something, it takes away that last 2%.

You're already prepared to live as a zombie.

Freeman: By the time we reach adulthood,

most of our daily lives are spent engaging

in activities that require little conscious thought.

If we were to lose our ability to make conscious decisions,

life just might continue as normal.

Certainly, we wouldn't recognize it in ourselves,

and the scary thing is whether you could recognize it

in anyone else.

If there was a zombie apocalypse,

I don't think it would be like "World War Z."

I think we would be plain old normal human beings,

except we'd be a little bit different.

We'd be more like "invasion of the body snatchers,"

where we're ourselves, but we're not ourselves anymore.

We humans love our free will.

As bizarre as it may seem,

it is entirely possible that a microscopic parasite

or technology run wild

could take away the free will we cherish so dearly.

All of this talk of zombie apocalypse

raises one final question --

why do we enjoy scaring ourselves half to death?

Maybe that's what we need to do

in order to prepare for the worst.

I'm not scared, because science is our best defense.

== sync, corrected by elderman == @elder_man

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