Does the brain have a sex?

This is obviously a fundamental
question that everyone asks.

So, according to initial popular belief:

Women have a brain smaller than men,

therefore, they would be 
less intelligent than men.

This idea stemmed from the 19th century,

during the heyday of craniometry

when doctors were interested to find 
links between the size of the skull,

the weight of the brain and intelligence.

It's important to note 
that for most of them

it was absolutely obvious and natural
that men had a bigger brain than women,

whites bigger than blacks

and managers bigger than workers.

A big supporter of these theories,

is the French doctor Paul Broca

who measured a difference of 150 grams

between average weights
of men's and women's brains,

men's weight was 1.350 kg

and women's 1.200 kg.

In 1861, Broca stated:

"We wondered if the smallness
of a woman's brain did not solely depend

on the smallness of her body, 
nevertheless, one should not forget

that women on average 
are a little less intelligent than men."

So, anyway,

this question of link between 
the size of the brain and intelligence

is not asked anymore,

because the reality is, there is 
no relation between the two,

and we know it thanks
to a certain number of male celebrities,

not women, who have given 
their brains to science.

A prominent person
like Anatole France, for example,

had a brain that weighed one kilogram,

Tourgueniev had a brain that weighed 2 kg,

and as for Einstein,
he had a small brain weighing 1.250 kg.

Meaning, of the same size as women's.

Another popular belief: women are skilled
at doing more than one thing at a time

because the communications
between their brain's hemispheres

are more developed as oppose to men's.

We know very well, they're multi-tasking.
This idea comes from a study

published in 1982,

on 20 brains conserved in formalin

that showed that the corpus callosum,

that's the part surrounded by red,

the bundle of fibers that connects 
both cerebral hemispheres,

that corpus callosum was thicker
for women than it was for men,

where perhaps better communication stems.

Now, since 1982, many things have gone by,

new technology developed,

in particular the new techniques
of cerebral imagery such as MRI

which made it possible
from then on to live the dream,

meaning to study a live brain
no more studying a brain in formalin.

And if we gather the collection of studies

made on this corpus callosum 
since MRI was invented,

we realize that there is no difference
between men and women

in the thickness of the corpus callosum.

Another popular belief:

"Women are more capable 
at learning languages

because they use both 
of their hemispheres to speak."

Let's see where this also comes from:

this comes from a study
that was published in 1994,

a study using MRI during a language test,

and it showed that men, taking this test,

activated one hemisphere 
whereas women used both.

So, this study that was conducted 
on 19 men and women,

intrigued numerous researchers who
looked into reproducing these results.

And if we were to gather now
the collection of studies

that were published between 1995
and 2009, including this one,

in total, 700 men and women were tested,

we find that statically speaking,

there is no difference 
between men and women

in the distribution of language areas.

And in fact, once a great number
of subjects were analyzed,

the difference between the sexes, 
finally, disappeared.

We will see why.

Take this example, a study using MRI,

where we asked the subjects
to do a mental calculation

that they were all successful at doing.

We could then see
that in the women's group,

there was actually a great variability

in the distribution of areas in the brain

that were activated 
during this calculation.

This variability was equally 
found in the men's group.

Finally, to come to an even score
for mental calculation,

each individual has their own way 
of activating their brain,

corresponding to many different strategies

to do mental calculations.

And, consequently, 
the variability that we can observe

between the individuals of the same sex,

equals or exceeds
the variability between the sexes.

Another popular belief:

the differences of mental 
aptitudes between the sexes

originates from a biological origin.

There are indeed a certain number of tests

where women are known to perform better.

For example tests
of visual perception of details,

such as this test here

where one must notice two identical houses

and the women are also better 
at tests of verbal fluency,

where a maximum number 
of words must be said

beginning with the same letter.

In short, all this is still 
not very complicated.

When it comes to men, they are better,
or known to be better anyways,

at tests involving mental 
rotation of objects in 3D.

They are equally better 
at reaching a target.

So, based on the significance
of these differences in performance,

we can ask the question:
Are they inherent or are they acquired?

In fact, it must be noted 
that the differences in question

are detectable only in adolescence,

and that they disappear with learning.

Therefore, we can assume
that education and culture

play an important role 
in the emergence of these differences.

There is also another important factor,
which is the context

where these prominent tests are carried.

Let's take then this prominent test
of mental rotation in 3D,

where one must say 
if the objects presented

are the same or if they are different.

If the test is given in a classroom

and the teacher says 
this is a geometry test,

at that moment,
boys will be better than girls.

But if the teacher initially makes
an announcement that this is an art test,

at that moment, boys and girls
will have the same scores.

So, these results are interesting

which show how much self-esteem
and gender stereotypes

affect the results of the tests.

Another example also is the difference
in mathematical performances

between boys and girls, 
in the United States.

A large-scale statistical survey
conducted on 10 million students

in 1990, showed, on average,

boys were a little better
than girls at math tests,

and some have interpreted 
these results saying

that it was because girls did not have 
a brain made for math.

But the same survey 
that was commissioned in 2008,

shows equivalent scores
for boys and girls.

So, for 20 years we had a disappearance
of performance differences in math

between boys and girls,

which clearly shows 
that it's the education

and not the biology that explains 
these differences in scores.

Now, we will ask the question:

"How does education affect the brain?"

Our human brains are made up 
of 100 billion neurons

that are connected to each other

thanks to connections
amounting to many billions.

Now 90% of these connections 
develop after birth.

And it's precisely on how these 
connections will come to be,

that these networks 
of neurons will develop,

and where education and culture 
will play an important part.

First example: 
brains of professional pianists,

also applicable for violinists,
I assure you,

we can observe the MRI, for these people,

a thickness of the cerebral regions

which control the coordination
of fingers as well as the hearing.

In fact, this phenomenon of thickness

is due to the connections produced
between the extra neurons

and in addition it is proportional

to the time spent learning
the piano since childhood.

And we use the term cerebral plasticity

to describe the brain's ability

at shaping up eventually 
to reflect experience.

Another example of cerebral
plasticity in adulthood.

We take a group
of twenty -year-old students

and we ask them to learn 
to juggle three balls.

And in just three months,

we find this phenomenon
of the cortex thickening

in the regions that control
the motor coordination and vision.

So, what's really interesting
in this experiment is

that if the students
stop practice juggling,

eventually the regions
that thickened before will shrink.

And so, we strongly went ahead
with this experiment

with people who are 
a little bit older, in their sixties,

and we find the same phenomenon
of thickness as the young ones.

It is still rather reassuring,

it shows that cerebral plasticity 
persists with age.

Here we have an example
extremely extraordinary

of cerebral plasticity.

A man who is 44 years old, 
married with two kids,

living a professional life
completely normal,

who suffered from slight 
weakness in his leg.

We decided to do an MRI test
and surprise surprise,

we discovered that his skull
was essentially full of liquid

and his brain was reduced to a thin layer

flattened along 
the inner lining of the skull.

We then asked questions.

And, it turns out, this person 
suffered from hydrocephalus from birth,

so we placed a drain 
at the base of the skull

to discharge the excess liquid,
but the drain was clogged

and finally the pressure
of the liquid repressed the brain

along the inner lining of the skull.

And all this happened without causing 
any trouble in this patient's life

who never suspected anything.

So, now that you know
everything on cerebral plasticity,

in terms of the brain's structure
and function

which is modified in relation
to history for each person,

you can now then understand
why we all have very different brains,

regardless of sex.

However, what we do have in common

is this cerebral cortex 
gifted with plasticity

which has greatly developed 
in the course of evolution

and which had to crease in order 
to fit inside the cranium.

You have here in front of you, 
to the left, a real brain

and to the right, a model brain
with the technological means,

we can have fun by unfolding it virtually.

And I will give you this experience.

Here I am unveiling the brain,

well, the skull, actually.

I am opening the cranium

and I am unfolding the cerebral cortex

which measures 2 m² on 3 mm of thickness,

and it's because of this cerebral cortex
that all of us, men and women,

are able to reason, to think,

to dream and to imagine
the future of humanity.

Thank you.

(Applause)