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's 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)