Original subtitles

[MUSIC PLAYING]

This is not a stomach.

It's a hub of intelligence.

It houses the equivalent of a small pet's brain.

[NON-ENGLISH SPEECH]

We have 200 million neurons in our gut about as many

as Timmy has in his cortex.

And we can say that Timmy is really very intelligent.

A cat and a dog each have about the same number

of nerve cells as the gut.

If they're intelligent, the gut is every bit as smart.

Scientists have some surprises in store for us,

having rediscovered what common sense has

known for a long time.

People of a nervous disposition get

butterflies in their stomach.

Cowards lack guts.

And we sometimes act on gut instinct

with the gut feeling of fear in the pit of our stomach.

At times, we get the distinct feeling our brains are not

the only captain on board.

But what exactly do scientists know about the interplay

between the gut and the brain?

The gut is home not just to millions of neurons,

but also to hundreds of billions of bacteria

that secretly influence our most daring exploits

and our personalities.

A voyage into the secret territory of our bowels

in search of our second brain.

[MUSIC PLAYING]

This story starts at Columbia University

in New York City when Michael Gershon dared

to proclaim that our gut houses a sensitive and intelligent

organ.

It's important to focus in the gut

to explain to the world this is one important dog.

And it's not just a repulsive serpentine

snake-like disgusting thing, but a vibrant lifeline to success.

So there was a dark age of knowledge of the second brain.

And then it was rediscovered.

And I helped to rediscover it.

And since it was a Renaissance, that

makes me the Leonardo of the bowel.

If Leonardo da Vinci had had the chance

to use the microscope Michael Gershon uses,

these are some of the neurons he would have observed.

200 million of these neurons line our intestine wall.

They span the length of our digestive tubes,

helping us to digest food.

Digestion is surprisingly complicated.

You have to do things that are very hard to do in

a laboratory-- break food down that you eat and make it

into tiny little molecules that you can absorb and use

to run your body.

And for that, you need a lot of nervous power.

[MUSIC PLAYING]

Our two brains resemble each other like brothers.

The upper brain houses the central nervous system.

And the lower brain houses the enteric nervous system.

They even share similar scientific names.

But did evolution really need to equip us

with two separate brains?

The reason that evolution would want to have this brain

outside is very similar to the reason

we all keep personal computers on our desks.

By peripheralizing it, sending it off to the gut,

it's more efficient, more effective.

The brain doesn't have to connect with huge cables

to the gut.

It can leave it there.

And you don't have to expand the brain to hold several million

more nerve cells.

[MUSIC PLAYING]

Scientist, Michel Neunlist, who

is based in Nantes in Western France,

is one of the world's leading experts

on the enteric nervous system.

For Michel in the history of our two brains,

the first brain is not the one we think it is.

[NON-ENGLISH SPEECH]

The second brain has had its name usurped really,

because I consider it to be the first brain, the original brain

even.

Primitive, multicellular organisms

were initially composed of just a digestive tube.

The enteric nervous system developed

within this digestive tube.

[MUSIC PLAYING]

If we travel back in time, it becomes apparent

that our upper brain evolved in order to better feed ourselves.

The appearance of the brain coincided

with that of our eyes and ears useful for seeking food.

Without dividing the tasks up like this,

we would still be spending all our energy

digesting, digesting, and digesting some more.

[MUSIC PLAYING]

The turning point in this spectacular evolution

of our brain is linked to a technological invention,

the domestication of fire.

1.5 million years ago, Homo sapiens

was still called Homo ergaster.

And he had just invented the barbecue.

[NON-ENGLISH SPEECH]

Cooking is a form of pre-digestion.

So thanks to cooking first, chewing became easier.

And we, therefore, invested less energy and physical effort.

Secondly, when cooked food arrives in the stomach,

digestion is easy.

And we can recuperate 16 times more energy

with a lot less investment.

As the first brain worked well, the second brain

took advantage of that and was able to develop.

In theory, it could not have happened at all, but it did.

[MUSIC PLAYING]

[NON-ENGLISH SPEECH]

Cooking our food meant that we could

jump some physiological hurdles, in other words, the constraints

linked to the available energy a large brain needed.

And from there, from Homo ergaster onwards,

the first brains, which measured 700 to 800 cubic centimeters,

gradually evolved over hundreds of thousands of years

into very large brains, like for example,

those of Neanderthal man or Cro-Magnon.

Cro-Magnon, that's you and me.

This brain increased to 1,500 to 1,600 cubic centimeters

without any change in body size.

[MUSIC PLAYING]

So our brain evolved.

And now, we can think of something other

than our stomachs.

Thinking on one side and digesting

on the other-- a neat division of tasks in theory.

But as always, the reality is more complex-- firstly,

because our two nervous systems, which

are connected by the vagus nerve,

are in constant conversation, secondly,

because the brain and the stomach

use the same neurotransmitters.

Neurotransmission is the language

that nerve cells speak in order to talk to one another.

And neurotransmitters are the words

that each nerve cell puts out that another nerve

cell can understand.

Now, serotonin is one of the words.

Serotonin, Michael Gershon has dedicated his life

to understanding the meaning of the word, which

changes according to the context it's in.

And this is what he has discovered.

In the upper brain, serotonin means well-being.

In the gut, it sets the pace for intestinal transit

and regulates our immune system.

It is depicted here in red, with the cells

of our intestine wall in blue.

But surprising as it may seem, 95% of our body's serotonin

is produced in our gut.

This serotonin acts on the digestive tube.

But also more surprisingly, it is

released into the bloodstream and acts on the brain,

in particular in the hypothalamus, which

is a zone that manages our emotions

and takes part in the regulation of emotions.

When the gut and brain converse,

the messages they exchange transit via the vagus nerve.

But we've known that for a long time now.

What researchers have just discovered

is that the serotonin that transits clandestinely

via the blood stream towards the brain

interferes with our emotions in a much more complex way.

Destined for the gut, this surplus of information,

which in theory has no real business being in the brain,

can sometimes lead to misunderstandings.

[NON-ENGLISH SPEECH]

We already knew that our emotions could indeed

influence our gut.

Now, what we're seeing is that our gut can also

influence our emotions.

Under normal conditions, the exchanges between gut and brain

take place without us even knowing about it,

making it difficult to study them.

But as always in science, by observing what goes wrong,

we can gain a better understanding

of how things work.

Irritable bowel syndrome, or IBS,

is unfortunately an obvious case study

for examining the communication problems that sometimes crop up

in the brain-gut couple.

It's a very common disease, affecting 1 in 10 people

and is characterized by severe abdominal pain.

[NON-ENGLISH SPEECH]

The syndrome is characterized by digestive difficulties,

abdominal pain, and a disruption of transit time,

but without us being able to find

any so-called organic malfunctions

from the various exams we carry out,

whether via colonoscopy, gastroscopy, scan.

That's why these people can't understand what's going on,

because we usually tell them, well, we've

run extensive tests, and we found nothing.

And they often say, but doctor, I'm in pain,

there's something wrong with me.

So it's important to explain to them that currently we

explain these function disorders by malfunctions occurring

between our brain and our digestive tube.

[MUSIC PLAYING]

What is causing these communication problems?

What is sending out the wrong messages-- our upper brain

or our lower one?

These questions are mobilizing researchers all over the world.

In Munich, Michael Schemann considers

that IBS could originate in the intestine wall.

Along with his team, he's trying to pierce

the mysteries of this neuron-packed area

of intestinal skin that lies at the crossroads of often

delicious, but sometimes painful sensations.

[NON-ENGLISH SPEECH]

It's hard to believe, but inside this sausage

is an enteric nervous system.

It's a typical Bavarian recipe-- white sausage,

and its skin is nothing other than a natural intestine, which

contains the enteric nervous system.

More than just dissecting sausages,

the researchers are cutting into intestines.

Their work involves measuring the activity

of human intestinal neurons.

[NON-ENGLISH SPEECH]

We're basing our work on the following hypothesis--

one of the causes of IBS is due to a faulty communication

between the mucosal surface and the gut nerves.

To test this hypothesis, Michael Schemann

compares the neuronal activity of the submucosal nerves

of healthy patients with those of ill patients.

And this is the result on an ill intestine.

This film is the very first visual presentation

of the signals that are emitted and received by the nerve

cells of our intestine.

It shows that the neurons of ill patients

are far more active than those of the healthy population.

[NON-ENGLISH SPEECH]

We conclude that these patients are indeed

suffering from a hypersensitive nervous system,

a sort of intestinal neurosis if you like.

[MUSIC PLAYING]

Michael Schemann hopes his discovery will soon

result in a drug that will normalize

this neuronal hyperactivity.

In the meantime, at the University Hospital

of Grenoble, Bruno Bonaz has observed

that the disease is often brought on by stress

or traumatic events.

He uses a more global method to provide relief

for his patients.

Do sit down.

Take slow, calm, deep breaths.

You're feeling serene.

You're smiling.

You're feeling very relaxed, nice and relaxed.

[NON-ENGLISH SPEECH]

Why does the stomach bear the brunt of all that?

I think there are lots of things we carry subconsciously

in our stomachs, which is where the idea of working

on that area with hypnosis comes from.

Hypnosis can, in particular, encourage

phenomena of adjusting to pain.

It means, these patients perceive less pain.

And their state of hypervigilance is reduced.

So they will perceive less pain.

And now, you can feel a pleasant feeling of warmth

in the area of your stomach around your abdomen.

Concentrate for a while on the gentle, pleasant warmth

you feel in your stomach.

If you imagine that the gut is sending signals

to the brain that are disturbing and the brain finds

these signals intolerable, hypnosis

can be used to essentially anesthetize

the brain to these signals.

So it's getting the same signals that are bad,

but because of hypnosis, they've suddenly become tolerable.

Although scientists don't understand the exact mechanisms

as yet, neuroimaging has enabled them

to localize the effects of hypnosis

on the brains of patients subjected to intestinal pain.

[NON-ENGLISH SPEECH]

Here, you have four cross sections of the brain.

When you experience abdominal pain,

you activate the zones that are represented here,

like the brain stem here, the thalamus, the insular cortex

here, the anterior cingulate cortex, and the frontal cortex.

And we now know that hypnosis can

modulate the activation of these zones that

are involved in pain.

So it's clear that hypnosis is not just all in the mind,

but is something that has a neural, anatomical,

and functional substratum.

[MUSIC PLAYING]

Scientists are only just beginning

to understand the secret silent conversation that takes

place between gut and brain.

Our minds are constantly influenced by our body's

internal chemistry.

Even our dreams, the most mysterious expression

of our inner lives, are particularly

sensitive to the serotonin emission

that happens during our sleep.

Could the unconscious, the notion

discovered back in ancient times and reinvented by Sigmund

Freud, be located in our gut?

The enteric nervous system can affect

how you feel by sending signals to the brain that do not

reach consciousness and can change the way

the brain perceives the world.

Your ability to think happily, your ability to think well,

your ability to resist depression and anxiety

can be very influenced by the messages

that the gut sends to the brain.

So to that extent, it's a contributor

to your unconscious.

[NON-ENGLISH SPEECH]

If we don't have emotions or feelings,

we become completely irrational.

Freud's approach is fascinating, because he said,

the ego is not master in its own house.

Well, perhaps not in the brain.

And perhaps, the ego's house is down there.

So perhaps, that ego is in the gut.

Yes, I like that idea.

Gastric psychoanalysis sounds good to me. [LAUGHTER]

[MUSIC PLAYING]

For the time being, gastric psychoanalysis

is still on the lookout for a founder.

But so striking is the anatomical similarity

between our two brains, that scientists

are starting to wonder very seriously

if the stomach and the head might not

share their illnesses as well.

Certain neurological illnesses, like Parkinson's disease,

may even originate in the gut.

The University Hospital of Nantes,

which receives 2,000 Parkinson's patients a year,

is the ideal place to study the hypothesis.

[NON-ENGLISH SPEECH]

We're going to do a few small movements to see

the current state of your condition.

Can you do this with your right hand?

Give it a little shake like this.

So that's difficult for you.

So in your day-to-day life, that must hamper all your actions,

like eating, for example.

It blocks.

It blocks.

He can't lift his arm.

He can't lift his arm.

So you have to help him.

Yeah, he can't feed himself.

For a long time, Parkinson's disease

was considered to be a condition that destroyed neurons located

in a particular area of the brain known as the substantia

nigra, which is Latin for black substance.

Yet, doctors have observed that the disease is often

also accompanied by major digestive disturbances.

Scientists have, therefore, put forward the theory

that it affects not only brain cells but also

our guts' neurons.

[NON-ENGLISH SPEECH]

Among certain patients prematurely,

before the first motor signs appear,

you can find signs of the digestive tract being affected,

such as constipation or an impairment

of the sense of smell.

So as this is rather premature, some researchers

have put forward the hypothesis that the disease could

originate peripherally and then spread gradually

along the nervous system and into the brain

and then, in a subsequent stage, become

far more widespread in the brain, which

would explain why patients develop intellectual impairment

and trouble with balance in the final phase of its development.

[MUSIC PLAYING]

The real origin of the disease,

whether it's in the gut or the brain,

has not yet been established.

But Michel Neunlist and the neurologist

of the University Hospital of Nantes

wanted to find out more about it.

In 2006, they decided to work together

to prove that Parkinson's disease can

be diagnosed via a simple intestinal biopsy of a living

patient.

Today, that task has been accomplished.

In a simple routine biopsy, there are 150 neurons.

And their condition reveals a lot about our brain neurons.

[NON-ENGLISH SPEECH]

What was observed among Parkinson's patients

was that, in these biopsies, lesions typical

of Parkinson's disease were found in the gut

neurons, the same lesions that were found

in the central nervous system.

This is an extraordinary result.

Whereas a biopsy of the brain is potentially

dangerous for the patient, an intestinal biopsy

is a harmless procedure.

[NON-ENGLISH SPEECH]

As a gastroenterologist, I would never

have imagined taking part in understanding or diagnosing

neurological diseases.

And yet, in the case of Parkinson's disease,

we can visualize and give information

on what is happening in the brain--

from our brain that is located in the intestine,

as though we were opening a window onto the brain.

And that's absolutely fantastic.

[MUSIC PLAYING]

What the scientists in Nantes have discovered

provides enormous hope.

In two or three years' time, they

hope to be able to carry out these routine biopsies

on people at risk.

Given that the digestive symptoms of the disease

can occur 20 years before the onset of motor symptoms,

an early diagnosis could enable earlier and, therefore,

more efficient treatment of the disease.

In the meantime, the idea of looking at the stomach

in order to better treat the mind is starting to gain ground

[NON-ENGLISH SPEECH]

The idea of the gut as an open window onto the brain

has been shown to be valid for Parkinson's disease.

The question we'll also be exploring now

is to try and see if this hypothesis applies

to other neurodegenerative diseases and, in particular,

Alzheimer's disease or other pathologies, this time more

neurodegenerative ones, but perhaps also behavioral ones,

such as autism and psychiatric pathologies.

[MUSIC PLAYING]

On closer inspection, our world

resembles a gut made up of tubes and entrails, in which fluids,

information, and signals circulate along

increasingly complex networks.

Science is only just starting to take into account

the complexity of these exchanges.

And their emerging properties remain to be discovered.

Yet, on the other side of the world,

traditional Chinese medicine has been

based on a vision of the human body

as a whole for thousands of years.

It endeavors to regulate the invisible energy flow that

circulates through our bodies.

In Chinese medicine, organs talk to each other and interact

via qi, an energy that connects us to the universe.

[NON-ENGLISH SPEECH]

The different medical systems are based

on their cultural context.

In Western medicine, we concentrate

on what is localized, dividing the body into different parts

to study specific functioning.

But Chinese medicine is based on a holistic, global vision

and focuses particularly on the relationship

between the different parts of the body.

Each of these two visions has its advantages.

[MUSIC PLAYING]

The gut expert of traditional Chinese medicine

is called Bo Zhi-yun.

We are in the CTM Hospital of Canton,

the largest hospital in the world

with 7 million patients a year.

[CROWD CHATTER]

Every day, its pharmacy dispenses

10 tons of drugs, both Western and

traditional Chinese medicine.

Here, acupuncture needles are used alongside state

of the art medical equipment.

The Chinese have been practicing acupuncture for 3,000 years,

although the gut was never previously

a predominant feature of it, until Dr. Bo discovered

abdominal acupuncture entirely by chance, a new practice

in the country of traditions.

[NON-ENGLISH SPEECH]

It was in 1972.

A lot of students were learning acupuncture,

and I had about 20 students trained in Western medicine.

One day, an old worker arrived in a wheelbarrow,

complaining of severe back pain.

I applied all the classic acupuncture methods,

but nothing worked.

The patient was in such pain, he was sweating profusely.

And I started getting nervous and broke out in a sweat

myself, because a lot of my students were watching me.

With his students gathered around him,

the professor could not lose face.

[NON-ENGLISH SPEECH]

I used two deep acupuncture points

located in the stomach along the Ren meridian.

The patient immediately stopped crying out.

And his face suddenly relaxed.

At the time, Professor Bo was highly surprised.

The location of these points in relation to the symptoms

was not logical.

He then embarked upon intensive research

to understand acupuncture in the abdomen.

And he discovered a highly sensitive zone

around the navel.

[NON-ENGLISH SPEECH]

The umbilical cord is the center

of the development of the human body,

plays a very important role in the growth of the embryo.

Even after the cord has been cut,

the navel continues to play a role

in coordinating the whole body.

But we don't know much about this hidden system.

Professor Bo's method is shown on these three illustrations.

He has trained over 5,000 disciples, who

now practice abdominal acupuncture in Asia, Europe,

and the United States.

[NON-ENGLISH SPEECH]

On these three images, we can see

that the organs and the viscera have a direct relationship

to our emotions and our mental state.

We can see clearly that the gut is closely related

to our brain.

Thanks to this discovery, Professor Bo

now treats numerous pathologies.

Today, a patient who suffers from depression

is consulting him.

[NON-ENGLISH SPEECH]

Has your condition improved?

[NON-ENGLISH SPEECH]

Yes, but it came back a while ago,

because there were problems in my family.

In traditional Chinese medicine,

we say that to cure the disease, you have to find the source.

And where is the source?

In the belly.

Lie down.

Let's start the session.

Under Professor Bo's needles, patients

suffering from Parkinson's, Alzheimer's, and depression

sometimes experience a regression of their symptoms

without Western science being able to understand

how the magic works.

Should scientists just accept the idea

that there is an energy that is not described

in their medical anatomy books?

To try and better understand how his treatment works,

Professor Bo has recorded the MRIs of healthy patients

before and after a session of abdominal acupuncture.

[NON-ENGLISH SPEECH]

Using functional MRI, we compared the images

of the brain of a person before and after a session

of abdominal acupuncture.

After the acupuncture, there is an increase

in the number of activated zones.

The results show that abdominal acupuncture

can improve cognitive functioning

and regulate emotions.

[MUSIC PLAYING]

In both the East and the West, scientists

admit that they are a long way from understanding everything

about the brain-gut axis.

But their research so far has led

to an astonishing discovery.

100,000 billion bacteria live in our digestive tube.

There are 1,000 times more bacteria inside each one of us

than stars in our galaxy.

This micro cosmos within a macro cosmos

is the most concentrated ecosystem on the planet.

There are 100 times more bacteria

in our gut than cells in our whole body.

[NON-ENGLISH SPEECH]

I'm a human being.

My cells come from the egg that was

the result of the fertilization of the ovum of my mother

by the spermatozoa of my father.

All those cells that proliferated

have made up my body.

Until not very long ago, I thought that was me.

But then I discovered that was not so.

In fact, that's just a little part of me.

There's an enormous part of me that's made up

of microscopic bacteria.

I am, in fact, an ecosystem.

We are more bacteria than we are human.

We have many more bacterial cells on our bodies--

on our bodies, in our bodies-- than we have human cells.

We have more bacterial DNA than we have human DNA.

So we are like passengers inside a bacterial bus, if you will.

At McMaster University in Hamilton, Canada,

Stephen Collins is seeking to understand the functioning

of this organized ecosystem that researchers now

call microbiota.

We each carry one to two kilos of bacteria inside us.

They generate about 30% of our caloric intake,

because a lot of the food that we eat we cannot digest.

But the bacteria can digest it for us.

And we take the energy.

We offer the bacteria board and lodging.

And in exchange, they convert our food into energy.

They help us determine what is and isn't toxic for our body.

Without bacteria, survival would be difficult.

The immune system in your gut, which

is the biggest immune system in the body,

is educated by what the bacteria inform it and tell it.

So the exposure to lots and lots of bacteria

keeps the immune system alert.

Attention!

To the world at large, we are merely

germs-- small, significant bacterial growth.

But today, we stand united, knowing full well

the glorious reward that awaits each and every one of us.

Sure, we're just germs--

As microbes play such a crucial role for our health,

it is of critical importance to understand the mechanisms

of microbial colonization.

Ready, sir.

Do me proud.

Dip one, two, three.

Inside the mother's womb, the baby

lives in a sterile environment.

But starting from the first day of his or her life,

he or she will be colonized by hundreds

of billions of microbes.

The first bacteria to settle inside the intestine

will select the newly arriving bacteria

until things stabilize, making up a personal signature,

like a sort of fingerprint.

[MUSIC PLAYING]

Events, such as taking antibiotics by the mother

or by the child, birth by cesarean section,

bottle feeding rather than breastfeeding,

and an excess of hygiene all reduce bacterial contact

and weaken the infant's microbiota.

I think sometime in the future, I don't know when,

that babies will be born with and given

the best possible flora, that it will be given,

not only to babies to colonize them properly,

but it will be given the various stages through life,

particularly as one gets older, to reinforce the microbiome.

[MUSIC PLAYING]

To find the recipe of the ideal microbiota,

it is first necessary to know which bacteria it contains.

At the National Institute of Agronomic Research in France,

Dusko Ehrlich endeavors to shed light

on the mysterious population that has lived inside us

ever since Eve bit into the apple of knowledge.

In order to do so, he has decided

to study the genome of our entire microbiota.

That's right, study the genome of an organism made up

of 100,000 billion bacteria.

This discrete project, called program MetaHIT,

is a great deal more ambitious than decoding the human genome.

10 years ago, I asked myself, what

would be most fun for a microbiologist

to do in his professional life?

And it was very clear.

Worldwide, we had huge sequencing capacity,

because human genome was sequenced.

And genome of monkeys and worms and flies were sequenced.

So couldn't we use that capacity to sequence not only

our genome, but also our metagenome.

The mammoth task ended in 2010,

when researchers published the map

of a human microbial metagenome and ended up

with a catalog of 3 million genes.

The vast project resulted in a surprising discovery.

We discovered so many things, I couldn't even

begin to tell you.

But one of the most surprising discoveries

was that we humans can be placed in three groups

by the microbial populations that live in our gut.

We call these groups enterotypes.

[MUSIC PLAYING]

So in addition to blood groups,

we are divided into three intestinal bacteria groups

that Dusko calls enterotypes.

Their difference lies in their capacity

to convert food into energy.

All three produce vitamins, but to varying degrees.

The enterotypes doesn't seem to be

related to geographical localization, race, sex, age.

And yes, one could have much closer enterotype to a Japanese

than to his own neighbor.

[MUSIC PLAYING]

Is it our genes, our environment, our food?

Dusko and his colleagues have not yet

understood what determines these three enterotypes.

But they are trying to determine how

the thousands of species of bacteria

interact with our body.

The scientist's long-term aim is to gain a better understanding

of the role bacteria play in the onset

of certain chronic diseases.

We're all familiar with blood and urine samples.

Soon, doctors will analyze our stools

to find out the exact composition of our microbiota.

It's evolutionary way of diagnostic.

Well, we see predisposition for diabetes, type 2 diabetes,

their disposition for cardiovascular disease,

the disposition for liver disease

just by examining microbiota in people.

[MUSIC PLAYING]

Studying the bacterial flora of obese people,

scientist Patrice Cani made an extremely promising discovery.

He observed that a certain type of bacteria, Akkermansia

muciniphila, which abounds in the intestines

of a healthy population, is extremely

rare in an obese population.

He, therefore, wanted to examine the purpose it serves.

To do so, his team fed mice a fat rich diet

and watched how they got fatter with and without Akkermansia.

The experiment yielded incredible results.

By ingesting the same quantity of energy of fat rich food,

the animals which received the bacteria

took twice as long to get fatter.

What we were able to demonstrate is

that the adipose tissue of the animals that

received a fact rich diet but were treated with the bacteria

stocked less energy.

[MUSIC PLAYING]

Akkermansia lives in the mucus layer that lines

and protects our intestinal cells

and that enables it to converse with our cells.

[MUSIC PLAYING]

Scientists have succeeded in finding out

how these bacteria communicate with the cells

of the intestinal wall of mice.

[NON-ENGLISH SPEECH]

In this experiment, we are analyzing the mouse's genes.

What we were able to demonstrate is

that the bacteria Akkermansia was

able to activate the mouse's genes

that induce an increase in the mouse's capacity to burn fat

with the result that the mouse gets half as

fat, has half the body fat of a mouse that does not

receive the bacteria.

[MUSIC PLAYING]

This test tube may well contain the goose

that lays the golden egg.

We will soon be eating this living bacteria,

either in a yogurt or by popping a pill.

But will it really help us fight obesity?

[NON-ENGLISH SPEECH]

From a therapeutic point of view,

the aim is to improve the conditions

of patients suffering from obesity and type 2 diabetes.

The aim is not-- and besides, it would never

work-- to say to people that we can administer this bacteria

to them and they can eat whatever they want

and still be protected from obesity.

I don't think that's possible.

[MUSIC PLAYING]

Today, scientists estimate that obesity is due

10% to genetic factors, 10% to bacteria,

and 80% to our behavior.

It, therefore, greatly depends on our own will.

But when we talk about will, does that necessarily

mean we are the only ones to decide?

Is our brain the master mind of our personality,

or is it acting under influence?

It is here, in Stephen Collins' ultra sterile laboratory,

that the answer may lie.

If you take a germ-free mouse that has no bacteria,

the mouse behaves in a very strange way.

It takes risks.

It is almost irresponsible.

When you put bacteria into these mice, their behavior changes.

They take no more risks.

They are very careful.

Why is this?

So maybe, the bacteria are saying,

look, we want to survive, so you better behave well.

But Stephen Collins does not stop

at this simple observation.

In this experiment, he chose two lines of mouse-- one

rather active and daring, the other rather calm.

Then he administered to each line

the microbiota of the other line of mouse.

We took mice that were very quiet,

and we put their microbiota into mice that

are notoriously aggressive.

And these are Swiss mice.

And the Swiss mice became calmer.

Then we did the other experiment.

We took mice that were very quiet,

and then we gave them the microbiota

from the aggressive mice.

And the calm became more aggressive.

[MUSIC PLAYING]

That's the experimental evidence,

that the microbiota influence the brain.

Who we are is not determined solely by us as humans.

We're being influenced by our ancestors--

the bacteria that were present on this Earth for millions

of years before us that have acquired a genetic repertoire

that is much greater than ours.

And now, we find that they influence who we are

and how we are.

[MUSIC PLAYING]

The results of Stephen Collins' demonstration

have toured the world.

In Europe, other scientists are making mice more adventurous

simply by making them eat bacteria.

[NON-ENGLISH SPEECH]

We already knew about a few of those features

among a certain number of parasites-- not bacteria,

but small eukaryotes which live inside organisms

and change the behavior of these organisms

by serving their own interests.

The example of toxoplasmosis is an amusing one,

because when these small parasites are present

in mice, they remove the mice's fear of cats.

Certain studies even suggest that the mice are sexually

attracted to the cats, which is strange.

Of course, that results in them getting

eaten by the cat, which serves the interest of the toxoplasma,

because toxoplasma develops well in cats.

[VIDEO PLAYBACK]

[MUSIC PLAYING]

-(SINGING) Who put her in?

Little Herman Grin.

Who pulled her out? [LAUGHING] Ding

dong dell, ding dong-- huh?

[NON-ENGLISH SPEECH]

And there are many examples of this.

It's very common for parasites living in the gut of their host

organism--

[END PLAYBACK]

--to alter its behavior.

It shows to what extent there is an interaction between what

happens in a person's gut and what that person's brain

will order them to do.

[MUSIC PLAYING]

But before concluding that we are being manipulated

by bacteria, it is necessary to prove

that what happens in mice can be transposed to humans.

In order to modify human intestinal flora,

we have two tools-- antibiotics to kill bad bacteria

and probiotics to develop good ones.

Probiotics are yeast and live bacteria

that are supposedly beneficial for health.

They can be found in yogurts, for example.

There is still some doubt as to their real efficacy,

given that research on them is in part funded

by those who market them.

In Europe, food industry groups have

been asked to remove all allegations of health benefits

from their probiotic-enriched milk-based products.

What's more, evaluating the efficacy of probiotics

is no easy matter.

[NON-ENGLISH SPEECH]

Life is not simple, even among bacteria.

One single bacterium is factory that

makes thousands of molecules.

And generally to make things even more difficult,

a preparation of probiotic bacteria

contain several of these bacteria,

increasing the complexity even more.

So we're a long way from the classic one

molecule, one action standard.

[NON-ENGLISH SPEECH]

We don't understand exactly how it works.

We know how to kill the bad ones with antibiotics

and how to try to favor the good ones by giving probiotics.

But in fact for the moment, we really

don't understand very much.

[MUSIC PLAYING]

At the Center for Neurobiology of Stress in Los Angeles,

Kirsten Tillisch was also skeptical.

How could taking probiotics have an effect on stress response?

To find out more, Kirsten and her team

tested the effect of probiotics on the brains of healthy women.

What we decided to do is look at healthy women, who

had no pain, no discomfort, no gastrointestinal, no anxiety

or depression.

And the task that we chose is a task

that's been used to look at how people respond

to emotionally negative images.

[MUSIC PLAYING]

And we thought, well, let's see if changing what's in the gut

can change the responsiveness to these images.

For two weeks, scientists gave a group of 60,

perfectly healthy women yogurts with and without probiotics.

Then they looked to see if their brains responded differently

to stress.

Are you ready to start the task?

OK, here we go.

So what we found was that in people who took the probiotic,

a network of brain regions was less active.

So it implies that the people who took probiotics

are less reactive to those images.

We know that in the brain something

is changing in the way that they're

responding to their environment and specifically

to negative and potentially threatening

things in their environment.

So this is the first study that has

shown that if you give a probiotic,

it changes something in the brain.

This is incredibly exciting to us, that with this simple food

that I could go to the market and buy,

potentially I could change something

that's going on in my brain.

[MUSIC PLAYING]

But even the most enthusiastic scientists

recommend exercising caution in the face

of this very recent research, especially given that, as yet,

we don't know much about the side effects of bacteria

on our body.

But all agree that they have an affect both on our health

and on our brains.

We now have to recognize that a certain component

input into our brain comes from bacteria.

Doesn't mean we are controlled by bacteria.

But they certainly have an influence in who we are, in

how we behave and how we react.

So I think, we now have to consider

that we have a third brain.

We have the big brain.

We have the little Brian.

And now, we have the intelligence of bacteria.

[MUSIC PLAYING]

[NON-ENGLISH SPEECH]

In science, we don't just progress by making discoveries.

We also progress by changing models or paradigms.

What we are is linked to our history and our environments.

These environments are external and we're now

discovering internal.

And that's wonderful.

[NON-ENGLISH SPEECH]

We tend to think, here we are.

We're all humans.

We sit staring at our screens with a strong sense

of our own individuality, thinking that ecosystems

are outside the forests, the fields, the Amazon,

that that's not us.

But in reality, things don't work like that.

We have this bacterial flora inside of us.

And it also exists outside of us too.

So in fact, we're bathing in a bacterial ecosystem

that penetrates us and is part of us.

There's no longer this separation between ourselves

and what is not ourselves, between the exterior,

between me and the others.

There's one absolutely remarkable

biological continuity.

Scientists' vision of our body has changed.

What we formerly took for the ultimate foundation of reality,

our individuality, is very probably the reflection

of a more complex reality, essentially

made up of messages, networks, and still

very mysterious connections.

We are now thousands of genes, billions of neurons,

and hundreds of billions of bacteria.

We are a multitude of links and information.

Their overwhelming complexity reaches

far beyond the confines of our own selves.

[MUSIC PLAYING]