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Can we, as adults, grow new nerve cells?

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There's still some confusion 
about that question,

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as this is a fairly new field of research.

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For example, I was talking
to one of my colleagues, Robert --

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who is an oncologist --

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and he was telling me,

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"Sandrine, this is puzzling,


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some of my patients that have been told
they are cured of their cancer,

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still develop symptoms of depression."

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And I responded to him,

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"Well, from my point of view 
that makes sense.

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The drug you give to your patients
that stops the cancer cells multiplying,

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also stops the newborn neurons
being generated in their brain."

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And then Robert looked at me 
like I was crazy and said,

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"But Sandrine, these are adult patients,
adults do not grow new nerve cells."

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And much to his surprise, I said,
"Well actually, we do."

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And this is a phenomenon 
that we call Neurogenesis.

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[Neurogenesis]

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Now, Robert is not a neuroscientist,
so when he went to medical school,

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so when he went to medical school
he was not taught what we know now --

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that the adult brain 
can generate new nerve cells.

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So, Robert, you know, 
being a good doctor that he is,

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wanted to come to my lab to understand
the topic a little bit better.

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And I took him for a tour

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of one the of most exciting
parts of the brain,

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when it comes to Neurogenesis --

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and this is the Hippocampus.

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So this is this gray structure
in the center of the brain.

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And what we've known for what
seems like already for very long,

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is that this is important for learning,
memory, mood and emotion.

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However, what we have learned
more recently,

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is that this is one of the unique
structures of the adult brain

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where new neurons can be generated.

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And if we slide 
through the Hippocampus

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and zoom in,

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what you actually see here in blue

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is a newborn neuron
in an adult mouse brain.

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So when it comes to the human brain,

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my colleague Dr. Jonas Frisén
from the Karolinska Institute,

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has estimated that we produce

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700 new neurons per day
in the Hippocampus.

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So you might think this is not much

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according to the billions
of neurons we have,

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but by the time we will turn 50,

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we will have all exchanged the neurons
we were born with in that structure

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with adult-born neurons.

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So, why are these neurons important
and what are their functions?

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So first, we know that they're important
for learning and memory.

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And in the lab we have shown

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that if we block the ability
of the adult brain

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to produce new neurons
in the Hippocampus,

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then we block certain memory abilities.

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And this is especially new and true
for spacial recognition.

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So like, how you navigate
your way in the city.

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So we are still learning a lot,

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and we are not only important
for memory capacity,

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but also for the quality of the memory.

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And we will be helpful to add time
to our memory

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and we will help differentiate
very similar memories.

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Like, how do you find your bike


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but you park at this station
everyday in the same area

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but in a slightly different position?

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And more interesting 
to my colleague Robert,

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is the research we have been doing
on Neurogenesis and Depression.

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So in an animal model of depression,

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we see that we have
a lower level of neurogenesis,

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and if we give antidepressants,

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then we increase the production
of these newborn neurons.

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and we decrease
the symptoms of depression.

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establishing a clear link 
between neurogenesis

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and depression.

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But moreover, if you 
just block neurogenesis,

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then you block the efficiency
of the antidepressant.

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So by then, Robert had understood
that very likely,

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his patients were suffering
from depression

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even after being cured of their cancer

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because the cancer drug had stopped
the newborn neuron to be generated.

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And it will take time 
to generate new neurons

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that reach their normal functions.

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So, collectively, now,

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we think we have enough evidence to say
that Neurogenesis is a target of choice

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if we want to improve
memory information or mood,

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or even prevent their decline
associated with aging,

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or associated with stress.

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So the next question is,

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can we control Neurogenesis?

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The answer is yes.

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And we are now going to do a little quiz.

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So I'm going to give you a set
of behavior and acitivity

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and you tell me if you think
it will increase Neurogenesis

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or if it will decrease neurogenesis.

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Are we ready?

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Okay, let's go.

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So what about learning?
Increasing?

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Yes.

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So learning will increase the production
of these new neurons.

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How about stress?

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Yes, stress will decrease the production
of new neurons in the Hippocampus.

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How about sleep deprivation?

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Indeed, it will decrease Neurogenesis.

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How about sex?

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Oh wow!

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(Laughter)

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Yes, you are right, it will increase
the production of new neurons.

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However, it's all about balance here.

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We don't want to fall in a situation


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about too much sex 
leading to sleep deprivation.

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(Laughter)

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So how about getting older?

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So, neurogenesis' rate will decrease
as we get older,

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but this is still occuring.

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And then finally, how about running?

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So, I will let you judge
that one by yourself.

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So this is one of the first studies
that was carried out by one of my mentors,

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Prof. Rusty Gage for the Salk Institute,

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showing that the environment
can have an impact

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on the production of new neurons.

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And here you see a section
of the hippocampus of a mouse

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that had no running wheel in its cage.

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And the little black dots you see
are actually newborn neurons-to-be.

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And now, you see a section
of the hippocampus of a mouse

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that did have a running wheel in its cage.


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So you see the massive increase
in the black dots

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representing the new neurons-to-be.

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So activity impacts neurogenesis
but that's not all.

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What you eat will have an effect

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on the production of new neurons
in the hippocampus.

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So here we have a sample of diet --

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of nutrients that have been shown
to have efficacy.

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And I'm just going
to point a few out for you.

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So calorie restriction of 20%-30%
will increase neurogenesis.

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Intermittent fasting --

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so spaces of time between your meal --

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will increase neurogenesis.

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Intake of Flavonoids, which is contained
in dark chocolate or blueberries,

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which are contained
in dark chocolate or blueberries,

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will increase neurogenesis.

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Omega-3 fatty acids,

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present in fatty fish, like salmon,

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will increase the production
of these new neurons.

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Conversely, a diet rich
in High Saturated Fat,

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will have a negative impact
on neurogenesis.

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Ethanol --

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intake of alcohol --

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will decrease neurogenesis.

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However, not everything is lost --

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Resveratrol, which is
contained in red wine,

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has been shown to promote the survival
of these new neurons.

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So next time you are at a dinner party,

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you might want to reach for this possibly
"Neurogenesis-neutral" drink.

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(Laughter)

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And then finally, 
let me point out the last one --

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a quick one.

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So Japanese groups
are fascinated with food textures,

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and they have shown that actually
soft diet impairs neurogenesis,

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as opposed to food
that requires mastication,

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chewing, or crunchy food.

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So all of this data, where we need to look
at the cellular level,

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have been generated using animal models.

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But this diet has also been given
to human participants,

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and what we could see

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is that the diet modulates memory and mood
in the same way it modulates neurogenesis.

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Such as, calorie restriction will improve
memory capacity,

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whereas a high-fat diet will exacerbate
symptoms of depression.

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As opposed to Omega-3 fatty acids,
which increase neurogenesis,

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and also help to decrease
the symptoms of depression.

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So we think that the effect of diet
on mental health,

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on memory and mood,

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is actually mediated by the production
of the new neurons in the hippocampus.

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And it is not only what you eat,
but it's also the texture

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but it's also the texture
of the food when you eat it,

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and the amount you eat.

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On our side --

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neuroscientists interested
in neurogenesis --

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we need to understand better the function
of these new neurons,

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and how we can control their survival
and their production.

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We also need to find how to protect
the neurogenesis of Robert's patients.


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And on your side --

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I leave you in charge
of your Neurogenesis.

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Thank you.

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(Applause)

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Margaret Heffernan: 
Fantastic research, Sandrine!

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Now, I told you you changed my life --

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I now eat a lot of blueberries.

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I'm really interested
in the running thing --

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Do I have to run?

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Or is it really just about


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aerobic exercise
getting oxygen to the brain?

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Could it be any kind of vigorous exercise?

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Sandrine Thuret: So for the moment,

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we can't really say 
if it's just the running itself,

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but we think that anything that indeed
will increase the production --

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of moving the blood flow to the brain --

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should be beneficial.

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MH: Right, so I don't have
to get a running wheel in my office?

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ST: No, you don't!

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(Laughter)

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MH: Oh, what a relief!

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Okay, that's wonderful.

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Thank you so much.

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ST: Thank you, thank you.

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(Applause)