0:00:14.763,0:00:17.130
Does the brain have a sex?

0:00:17.130,0:00:22.521
This is obviously a fundamental[br]question that everyone asks.

0:00:22.521,0:00:24.777
So, according to initial popular belief:

0:00:24.777,0:00:27.763
Women have a brain smaller than men,

0:00:27.763,0:00:30.789
therefore, they would be [br]less intelligent than men.

0:00:30.789,0:00:33.516
This idea stemmed from the 19th century,

0:00:33.516,0:00:36.523
during the heyday of craniometry

0:00:36.523,0:00:41.532
when doctors were interested to find [br]links between the size of the skull,

0:00:41.532,0:00:43.723
the weight of the brain and intelligence.

0:00:43.723,0:00:46.155
It's important to note [br]that for most of them

0:00:46.155,0:00:50.749
it was absolutely obvious and natural[br]that men had a bigger brain than women,

0:00:50.749,0:00:52.748
whites bigger than blacks

0:00:52.748,0:00:54.739
and managers bigger than workers.

0:00:55.259,0:00:57.220
A big supporter of these theories,

0:00:57.220,0:00:59.761
is the French doctor Paul Broca

0:00:59.761,0:01:02.503
who measured a difference of 150 grams

0:01:02.503,0:01:05.483
between average weights[br]of men's and women's brains,

0:01:05.483,0:01:08.533
men's weight was 1.350 kg

0:01:08.533,0:01:10.232
and women's 1.200 kg.

0:01:10.232,0:01:14.471
In 1861, Broca stated:

0:01:14.471,0:01:18.752
"We wondered if the smallness[br]of a woman's brain did not solely depend

0:01:18.752,0:01:21.972
on the smallness of her body, [br]nevertheless, one should not forget

0:01:21.972,0:01:25.259
that women on average [br]are a little less intelligent than men."

0:01:25.769,0:01:28.761
So, anyway,

0:01:28.761,0:01:32.493
this question of link between [br]the size of the brain and intelligence

0:01:32.493,0:01:33.775
is not asked anymore,

0:01:33.775,0:01:37.047
because the reality is, there is [br]no relation between the two,

0:01:37.047,0:01:40.201
and we know it thanks[br]to a certain number of male celebrities,

0:01:40.201,0:01:42.776
not women, who have given [br]their brains to science.

0:01:42.776,0:01:45.765
A prominent person[br]like Anatole France, for example,

0:01:45.765,0:01:48.228
had a brain that weighed one kilogram,

0:01:48.228,0:01:50.751
Tourgueniev had a brain that weighed 2 kg,

0:01:50.751,0:01:54.096
and as for Einstein,[br]he had a small brain weighing 1.250 kg.

0:01:54.096,0:01:57.179
Meaning, of the same size as women's.

0:01:57.179,0:02:01.255
Another popular belief: women are skilled[br]at doing more than one thing at a time

0:02:01.255,0:02:04.428
because the communications[br]between their brain's hemispheres

0:02:04.428,0:02:06.290
are more developed as oppose to men's.

0:02:06.290,0:02:10.526
We know very well, they're multi-tasking.[br]This idea comes from a study

0:02:10.526,0:02:13.072
published in 1982,

0:02:13.072,0:02:15.548
on 20 brains conserved in formalin

0:02:15.548,0:02:18.265
that showed that the corpus callosum,

0:02:18.265,0:02:20.234
that's the part surrounded by red,

0:02:20.234,0:02:23.946
the bundle of fibers that connects [br]both cerebral hemispheres,

0:02:23.946,0:02:27.011
that corpus callosum was thicker[br]for women than it was for men,

0:02:27.011,0:02:29.193
where perhaps better communication stems.

0:02:29.193,0:02:34.004
Now, since 1982, many things have gone by,

0:02:34.004,0:02:35.770
new technology developed,

0:02:35.770,0:02:40.286
in particular the new techniques[br]of cerebral imagery such as MRI

0:02:40.286,0:02:43.233
which made it possible[br]from then on to live the dream,

0:02:43.233,0:02:47.528
meaning to study a live brain[br]no more studying a brain in formalin.

0:02:47.528,0:02:49.770
And if we gather the collection of studies

0:02:49.770,0:02:53.236
made on this corpus callosum [br]since MRI was invented,

0:02:53.236,0:02:56.103
we realize that there is no difference[br]between men and women

0:02:56.103,0:02:58.016
in the thickness of the corpus callosum.

0:02:58.016,0:02:59.519
Another popular belief:

0:02:59.519,0:03:02.253
"Women are more capable [br]at learning languages

0:03:02.253,0:03:05.061
because they use both [br]of their hemispheres to speak."

0:03:05.061,0:03:06.884
Let's see where this also comes from:

0:03:06.884,0:03:10.752
this comes from a study[br]that was published in 1994,

0:03:10.752,0:03:14.530
a study using MRI during a language test,

0:03:14.530,0:03:17.510
and it showed that men, taking this test,

0:03:17.510,0:03:20.708
activated one hemisphere [br]whereas women used both.

0:03:20.708,0:03:24.516
So, this study that was conducted [br]on 19 men and women,

0:03:24.516,0:03:28.794
intrigued numerous researchers who[br]looked into reproducing these results.

0:03:29.235,0:03:32.516
And if we were to gather now[br]the collection of studies

0:03:32.516,0:03:37.778
that were published between 1995[br]and 2009, including this one,

0:03:37.778,0:03:40.714
in total, 700 men and women were tested,

0:03:40.714,0:03:42.774
we find that statically speaking,

0:03:42.774,0:03:45.504
there is no difference [br]between men and women

0:03:45.504,0:03:48.761
in the distribution of language areas.

0:03:48.761,0:03:52.508
And in fact, once a great number[br]of subjects were analyzed,

0:03:52.508,0:03:56.256
the difference between the sexes, [br]finally, disappeared.

0:03:56.256,0:03:58.237
We will see why.

0:03:58.237,0:04:01.259
Take this example, a study using MRI,

0:04:01.259,0:04:04.441
where we asked the subjects[br]to do a mental calculation

0:04:04.441,0:04:07.022
that they were all successful at doing.

0:04:07.022,0:04:10.073
We could then see[br]that in the women's group,

0:04:10.073,0:04:12.824
there was actually a great variability

0:04:12.824,0:04:15.516
in the distribution of areas in the brain

0:04:15.516,0:04:17.710
that were activated [br]during this calculation.

0:04:17.710,0:04:21.504
This variability was equally [br]found in the men's group.

0:04:22.034,0:04:26.082
Finally, to come to an even score[br]for mental calculation,

0:04:26.082,0:04:30.281
each individual has their own way [br]of activating their brain,

0:04:30.281,0:04:34.112
corresponding to many different strategies

0:04:34.112,0:04:36.764
to do mental calculations.

0:04:36.764,0:04:40.532
And, consequently, [br]the variability that we can observe

0:04:40.532,0:04:43.260
between the individuals of the same sex,

0:04:43.260,0:04:46.954
equals or exceeds[br]the variability between the sexes.

0:04:48.284,0:04:49.646
Another popular belief:

0:04:49.646,0:04:52.565
the differences of mental [br]aptitudes between the sexes

0:04:52.565,0:04:54.941
originates from a biological origin.

0:04:54.961,0:04:57.417
There are indeed a certain number of tests

0:04:57.417,0:05:00.030
where women are known to perform better.

0:05:00.030,0:05:03.767
For example tests[br]of visual perception of details,

0:05:03.767,0:05:05.284
such as this test here

0:05:05.284,0:05:08.044
where one must notice two identical houses

0:05:08.044,0:05:11.742
and the women are also better [br]at tests of verbal fluency,

0:05:11.742,0:05:14.257
where a maximum number [br]of words must be said

0:05:14.257,0:05:15.784
beginning with the same letter.

0:05:15.784,0:05:18.263
In short, all this is still [br]not very complicated.

0:05:18.263,0:05:22.813
When it comes to men, they are better,[br]or known to be better anyways,

0:05:22.813,0:05:27.281
at tests involving mental [br]rotation of objects in 3D.

0:05:27.842,0:05:30.979
They are equally better [br]at reaching a target.

0:05:30.979,0:05:35.502
So, based on the significance[br]of these differences in performance,

0:05:35.502,0:05:39.498
we can ask the question:[br]Are they inherent or are they acquired?

0:05:39.498,0:05:42.531
In fact, it must be noted [br]that the differences in question

0:05:42.531,0:05:46.220
are detectable only in adolescence,

0:05:46.220,0:05:49.253
and that they disappear with learning.

0:05:49.253,0:05:52.511
Therefore, we can assume[br]that education and culture

0:05:52.511,0:05:55.738
play an important role [br]in the emergence of these differences.

0:05:55.738,0:06:00.002
There is also another important factor,[br]which is the context

0:06:00.002,0:06:03.498
where these prominent tests are carried.

0:06:03.498,0:06:08.228
Let's take then this prominent test[br]of mental rotation in 3D,

0:06:08.228,0:06:11.892
where one must say [br]if the objects presented

0:06:11.892,0:06:15.018
are the same or if they are different.

0:06:15.018,0:06:17.762
If the test is given in a classroom

0:06:17.762,0:06:21.796
and the teacher says [br]this is a geometry test,

0:06:21.796,0:06:25.319
at that moment,[br]boys will be better than girls.

0:06:25.319,0:06:30.143
But if the teacher initially makes[br]an announcement that this is an art test,

0:06:30.143,0:06:33.473
at that moment, boys and girls[br]will have the same scores.

0:06:33.473,0:06:35.504
So, these results are interesting

0:06:35.504,0:06:40.579
which show how much self-esteem[br]and gender stereotypes

0:06:40.579,0:06:43.269
affect the results of the tests.

0:06:45.419,0:06:48.634
Another example also is the difference[br]in mathematical performances

0:06:48.634,0:06:52.398
between boys and girls, [br]in the United States.

0:06:52.398,0:06:56.536
A large-scale statistical survey[br]conducted on 10 million students

0:06:56.536,0:06:59.525
in 1990, showed, on average,

0:06:59.525,0:07:03.238
boys were a little better[br]than girls at math tests,

0:07:03.238,0:07:05.910
and some have interpreted [br]these results saying

0:07:05.910,0:07:09.457
that it was because girls did not have [br]a brain made for math.

0:07:09.457,0:07:12.943
But the same survey [br]that was commissioned in 2008,

0:07:12.943,0:07:16.551
shows equivalent scores[br]for boys and girls.

0:07:17.011,0:07:21.771
So, for 20 years we had a disappearance[br]of performance differences in math

0:07:21.771,0:07:23.283
between boys and girls,

0:07:23.283,0:07:25.994
which clearly shows [br]that it's the education

0:07:25.994,0:07:30.093
and not the biology that explains [br]these differences in scores.

0:07:30.093,0:07:31.893
Now, we will ask the question:

0:07:31.893,0:07:34.815
"How does education affect the brain?"

0:07:35.515,0:07:40.054
Our human brains are made up [br]of 100 billion neurons

0:07:40.054,0:07:42.006
that are connected to each other

0:07:42.006,0:07:47.045
thanks to connections[br]amounting to many billions.

0:07:47.045,0:07:51.541
Now 90% of these connections [br]develop after birth.

0:07:51.541,0:07:56.278
And it's precisely on how these [br]connections will come to be,

0:07:56.278,0:07:58.778
that these networks [br]of neurons will develop,

0:07:58.778,0:08:02.507
and where education and culture [br]will play an important part.

0:08:02.967,0:08:06.273
First example: [br]brains of professional pianists,

0:08:06.273,0:08:09.394
also applicable for violinists,[br]I assure you,

0:08:09.394,0:08:11.767
we can observe the MRI, for these people,

0:08:11.767,0:08:14.518
a thickness of the cerebral regions

0:08:14.518,0:08:19.019
which control the coordination[br]of fingers as well as the hearing.

0:08:19.019,0:08:21.210
In fact, this phenomenon of thickness

0:08:21.210,0:08:25.771
is due to the connections produced[br]between the extra neurons

0:08:25.771,0:08:27.799
and in addition it is proportional

0:08:27.799,0:08:32.080
to the time spent learning[br]the piano since childhood.

0:08:32.080,0:08:35.279
And we use the term cerebral plasticity

0:08:35.279,0:08:38.169
to describe the brain's ability

0:08:38.169,0:08:41.832
at shaping up eventually [br]to reflect experience.

0:08:41.832,0:08:44.861
Another example of cerebral[br]plasticity in adulthood.

0:08:44.861,0:08:48.162
We take a group[br]of twenty -year-old students

0:08:48.162,0:08:50.964
and we ask them to learn [br]to juggle three balls.

0:08:50.964,0:08:52.435
And in just three months,

0:08:52.435,0:08:55.256
we find this phenomenon[br]of the cortex thickening

0:08:55.256,0:08:59.208
in the regions that control[br]the motor coordination and vision.

0:08:59.208,0:09:02.273
So, what's really interesting[br]in this experiment is

0:09:02.273,0:09:04.784
that if the students[br]stop practice juggling,

0:09:04.784,0:09:08.961
eventually the regions[br]that thickened before will shrink.

0:09:08.961,0:09:11.830
And so, we strongly went ahead[br]with this experiment

0:09:11.830,0:09:15.050
with people who are [br]a little bit older, in their sixties,

0:09:15.050,0:09:18.590
and we find the same phenomenon[br]of thickness as the young ones.

0:09:18.590,0:09:20.030
It is still rather reassuring,

0:09:20.030,0:09:24.271
it shows that cerebral plasticity [br]persists with age.

0:09:25.481,0:09:28.257
Here we have an example[br]extremely extraordinary

0:09:28.257,0:09:30.049
of cerebral plasticity.

0:09:30.049,0:09:34.403
A man who is 44 years old, [br]married with two kids,

0:09:34.403,0:09:37.264
living a professional life[br]completely normal,

0:09:37.264,0:09:40.488
who suffered from slight [br]weakness in his leg.

0:09:40.488,0:09:43.770
We decided to do an MRI test[br]and surprise surprise,

0:09:43.770,0:09:48.505
we discovered that his skull[br]was essentially full of liquid

0:09:48.505,0:09:51.718
and his brain was reduced to a thin layer

0:09:51.718,0:09:54.333
flattened along [br]the inner lining of the skull.

0:09:54.333,0:09:56.233
We then asked questions.

0:09:56.233,0:10:00.239
And, it turns out, this person [br]suffered from hydrocephalus from birth,

0:10:00.239,0:10:02.995
so we placed a drain [br]at the base of the skull

0:10:02.995,0:10:07.721
to discharge the excess liquid,[br]but the drain was clogged

0:10:07.721,0:10:11.233
and finally the pressure[br]of the liquid repressed the brain

0:10:11.233,0:10:13.001
along the inner lining of the skull.

0:10:13.001,0:10:17.234
And all this happened without causing [br]any trouble in this patient's life

0:10:17.234,0:10:19.364
who never suspected anything.

0:10:19.934,0:10:23.749
So, now that you know[br]everything on cerebral plasticity,

0:10:23.749,0:10:26.895
in terms of the brain's structure[br]and function

0:10:26.895,0:10:29.959
which is modified in relation[br]to history for each person,

0:10:29.959,0:10:33.754
you can now then understand[br]why we all have very different brains,

0:10:33.754,0:10:35.218
regardless of sex.

0:10:35.218,0:10:37.703
However, what we do have in common

0:10:37.703,0:10:41.043
is this cerebral cortex [br]gifted with plasticity

0:10:41.043,0:10:44.002
which has greatly developed [br]in the course of evolution

0:10:44.002,0:10:48.449
and which had to crease in order [br]to fit inside the cranium.

0:10:48.979,0:10:52.290
You have here in front of you, [br]to the left, a real brain

0:10:52.290,0:10:56.069
and to the right, a model brain[br]with the technological means,

0:10:56.069,0:10:59.648
we can have fun by unfolding it virtually.

0:10:59.648,0:11:01.929
And I will give you this experience.

0:11:02.879,0:11:06.520
Here I am unveiling the brain,

0:11:06.520,0:11:08.252
well, the skull, actually.

0:11:08.712,0:11:11.241
I am opening the cranium

0:11:11.241,0:11:13.310
and I am unfolding the cerebral cortex

0:11:13.310,0:11:17.231
which measures 2 m² on 3 mm of thickness,

0:11:17.231,0:11:21.280
and it's because of this cerebral cortex[br]that all of us, men and women,

0:11:21.280,0:11:23.521
are able to reason, to think,

0:11:23.521,0:11:27.207
to dream and to imagine[br]the future of humanity.

0:11:27.207,0:11:28.457
Thank you.

0:11:28.457,0:11:31.057
(Applause)