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Does the brain have a sex?

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This is obviously a fundamental
question that everyone asks.

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So, according to initial popular belief:

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Women have a brain smaller than men,

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therefore, they would be 
less intelligent than men.

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This idea stemmed from the 19th century,

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during the heyday of craniometry

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

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the weight of the brain and intelligence.

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It's important to note 
that for most of them

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

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whites bigger than blacks

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and managers bigger than workers.

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A big supporter of these theories,

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is the French doctor Paul Broca

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who measured a difference of 150 grams

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

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men's weight was 1.350 kg

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and women's 1.200 kg.

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In 1861, Broca stated:

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

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

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

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So, anyway,

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

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is not asked anymore,

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

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

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not women, who have given 
their brains to science.

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A prominent person like 
Anatole France, for example,

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had a brain that weighed one kilogram,

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Tourgueniev's had a brain
that weighed 2 kg,

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

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Meaning, of the same size as women's.

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

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because the communications
between their brain's hemispheres

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are more developed as oppose to men's.

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

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published in 1982,

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on 20 brains conserved in formalin

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that showed that the corpus callosum,

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that's the part surrounded by red,

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the bundle of fibers that connects 
both cerebral hemispheres,

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

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where perhaps better communication stems.

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Now, since 1982, many things have gone by,

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new technology developed,

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in particular the new techniques
of cerebral imagery such as MRI

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

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

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And if we gather the collection of studies

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made on this corpus callosum 
since MRI was invented,

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we realize that there is no difference
between men and women

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in the thickness of the corpus callosum.

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Another popular belief:

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"Women are more capable 
at learning languages

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because they use both 
of their hemispheres to speak."

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Let's see where this also comes from:

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this comes from a study
that was published in 1994,

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a study using MRI during a language test,

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and it showed that men, taking this test,

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activated one hemisphere 
whereas women used both.

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

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intrigued numerous researchers who
looked into reproducing these results.

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And if we were to gather now
the collection of studies

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

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in total, 700 men and women were tested,

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we find that statically speaking,

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there is no difference 
between men and women

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in the distribution of language areas.

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

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the difference between the sexes, 
finally, disappeared.

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We will see why.

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Take this example, a study using MRI,

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where we asked the subjects
to do a mental calculation

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that they were all successful at doing.

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

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there was actually a great variability

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in the distribution of areas in the brain

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that were activated 
during this calculation.

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

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

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each individual has their own way 
of activating their brain,

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corresponding to many different strategies

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to do mental calculations.

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And, consequently, 
the variability that we can observe

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between the individuals of the same sex,

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equals or exceeds
the variability between the sexes.

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Another popular belief:

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the differences of mental 
aptitudes between the sexes

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originates from a biological origin.

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There are indeed a certain number of tests

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where women are known to perform better.

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For example tests
of visual perception of details,

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such as this test here

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where one must notice two identical houses

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

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where a maximum number 
of words must be said

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beginning with the same letter.

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In short, all this is still 
not very complicated.

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

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at tests involving mental 
rotation of objects in 3D.

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They are equally better 
at reaching a target.

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

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

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

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are detectable only in adolescence,

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and that they disappear with learning.

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Therefore, we can assume
that education and culture

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play an important role 
in the emergence of these differences.

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There is also another important factor,
which is the context

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where these prominent tests are carried.

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

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where one must say 
if the objects presented

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are the same or if they are different.

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If the test is given in a classroom

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and the teacher says 
this is a geometry test,

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at that moment,
boys will be better than girls.

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

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

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So, these results are interesting

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which show how much self-esteem
and gender stereotypes

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affect the results of the tests.

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Another example also is the difference
in mathematical performances

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between boys and girls, 
in the United States.

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A large-scale statistical survey
conducted on 10 million students

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in 1990, showed, on average,

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boys were a little better
than girls at math tests,

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and some have interpreted 
these results saying

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

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But the same survey 
that was commissioned in 2008,

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shows equivalent scores
for boys and girls.

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

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between boys and girls,

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which clearly shows 
that it's the education

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and not the biology that explains 
these differences in scores.

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Now, we will ask the question:

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"How does education affect the brain?"

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Our human brains are made up 
of 100 billion neurons

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that are connected to each other

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thanks to connections
amounting to many billions.

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Now 90% of these connections 
develop after birth.

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

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that these networks 
of neurons will develop,

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and where education and culture 
will play an important part.

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First example: 
brains of professional pianists,

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also applicable for violinists,
I assure you,

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we can observe the MRI, for these people,

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a thickness of the cerebral regions

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

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In fact, this phenomenon of thickness

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is due to the connections produced
between the extra neurons

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and in addition it is proportional

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to the time spent learning
the piano since childhood.

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And we use the term cerebral plasticity

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to describe the brain's ability

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at shaping up eventually 
to reflect experience.

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Another example of cerebral
plasticity in adulthood.

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We take a group
of twenty -year-old students

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and we ask them to learn 
to juggle three balls.

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And in just three months,

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we find this phenomenon
of the cortex thickening

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in the regions that control
the motor coordination and vision.

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So, what's really interesting
in this experiment is

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that if the students
stop practice juggling,

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eventually the regions
that thickened before will shrink.

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And so, we strongly went ahead
with this experiment

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

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

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It is still rather reassuring,

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it shows that cerebral plasticity 
persists with age.

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Here we have an example
extremely extraordinary

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of cerebral plasticity.

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

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living a professional life
completely normal,

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who suffered from slight 
weakness in his leg.

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We decided to do an MRI test
and surprise surprise,

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we discovered that his skull
was essentially full of liquid

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and his brain was reduced to a thin layer

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flattened along 
the inner lining of the skull.

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We then asked questions.

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

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so we placed a drain 
at the base of the skull

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to discharge the excess liquid,
but the drain was clogged

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and finally the pressure
of the liquid repressed the brain

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along the inner lining of the skull.

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

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who never suspected anything.

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So, now that you know
everything on cerebral plasticity,

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in terms of the brain's structure
and function

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which is modified in relation
to history for each person,

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

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regardless of sex.

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However, what we do have in common

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is this cerebral cortex 
gifted with plasticity

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which has greatly developed 
in the course of evolution

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

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

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

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we can have fun by unfolding it virtually.

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And I will give you this experience.

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Here I am unveiling the brain,

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well, the skull, actually.

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I am opening the cranium

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and I am unfolding the cerebral cortex

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which measures 2 m² on 3 mm of thickness,

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

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are able to reason, to think,

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to dream and to imagine
the future of humanity.

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Thank you.

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(Applause)