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Does the brain have a sex ? | Catherine Vidal | TEDxParis

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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)
Title:
Does the brain have a sex ? | Catherine Vidal | TEDxParis
Description:

Catherine Vidal debunks popular beliefs and preconceived ideas regarding the brain based on the reality of facts.

more » « less
Video Language:
French
Team:
closed TED
Project:
TEDxTalks
Duration:
11:38
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