You can grow new brain cells

 Can we, as adults, grow new nerve cells? There's still some confusionabout that question, as this is a fairly new field of research. For example, I was talkingto one of my colleagues, Robert, who is an oncologist, and he was telling me, "Sandrine, this is puzzling. Some of my patients that have been toldthey are cured of their cancer still develop symptoms of depression." And I responded to him, "Well, from my point of viewthat makes sense. The drug you give to your patientsthat stops the cancer cells multiplying also stops the newborn neuronsbeing generated in their brain."

 And then Robert looked at melike I was crazy and said, "But Sandrine, these are adult patients -- adults do not grow new nerve cells." And much to his surprise, I said,"Well actually, we do." And this is a phenomenonthat we call neurogenesis. [Neurogenesis] Now Robert is not a neuroscientist, and when he went to medical schoolhe was not taught what we know now -- that the adult braincan generate new nerve cells. So Robert, you know,being the good doctor that he is, wanted to come to my lab to understand the topica little bit better. And I took him for a tour of one of the most excitingparts of the brain when it comes to neurogenesis -- and this is the hippocampus. 

So this is this gray structurein the center of the brain. And what we've known alreadyfor very long, is that this is important for learning,memory, mood and emotion. However, what wehave learned more recently is that this is one of the uniquestructures of the adult brain where new neurons can be generated. And if we slice through the hippocampus and zoom in, what you actually see here in blue is a newborn neuronin an adult mouse brain. So when it comes to the human brain -- my colleague Jonas Frisénfrom the Karolinska Institutet, has estimated that we produce700 new neurons per day in the hippocampus.

 You might think this is not much, compared to the billionsof neurons we have. But by the time we turn 50, we will have all exchanged the neuronswe were born with in that structure with adult-born neurons. So why are these new neurons importantand what are their functions? First, we know that they're importantfor learning and memory. And in the lab we have shown that if we block the abilityof the adult brain to produce new neurons in the hippocampus, then we block certain memory abilities. And this is especially new and truefor spatial recognition -- so like, how you navigateyour way in the city. 

We are still learning a lot, and neurons are not only importantfor memory capacity, but also for the quality of the memory. And they will have been helpfulto add time to our memory and they will help differentiatevery similar memories, like: how do you find your bike that you park at the stationevery day in the same area, but in a slightly different position? And more interestingto my colleague Robert is the research we have been doingon neurogenesis and depression. So in an animal model of depression, we have seen that we havea lower level of neurogenesis. And if we give antidepressants, then we increase the productionof these newborn neurons, and we decreasethe symptoms of depression, establishing a clear linkbetween neurogenesis and depression. 

But moreover, if youjust block neurogenesis, then you block the efficacyof the antidepressant. So by then, Robert had understood that very likely his patientswere suffering from depression even after being cured of their cancer, because the cancer drug had stoppednewborn neurons from being generated. And it will take timeto generate new neurons that reach normal functions. So, collectively, now we thinkwe have enough evidence to say that neurogenesisis a target of choice if we want to improvememory formation or mood, or even prevent the declineassociated with aging, or associated with stress. So the next question is: can we control neurogenesis? The answer is yes. 

And we are now going to do a little quiz. I'm going to give you a setof behaviors and activities, and you tell me if you thinkthey will increase neurogenesis or if they will decrease neurogenesis. Are we ready? OK, let's go. So what about learning? Increasing? Yes. Learning will increase the productionof these new neurons. How about stress? Yes, stress will decrease the productionof new neurons in the hippocampus. How about sleep deprivation? Indeed, it will decrease neurogenesis. How about sex? Oh, wow! (Laughter) Yes, you are right, it will increasethe production of new neurons. However, it's all about balance here. We don't want to fall in a situation -- (Laughter) about too much sexleading to sleep deprivation. 

How about getting older? So the neurogenesis ratewill decrease as we get older, but it is still occurring. And then finally, how about running? I will let you judge that one by yourself. So this is one of the first studies that was carried out by one of my mentors,Rusty Gage from the Salk Institute, showing that the environmentcan have an impact on the production of new neurons. And here you see a sectionof the hippocampus of a mouse that had no running wheel in its cage. And the little black dots you seeare actually newborn neurons-to-be. And now, you see a sectionof the hippocampus of a mouse that had a running wheel in its cage. 

So you see the massive increase of the black dots representingthe new neurons-to-be. So activity impacts neurogenesis,but that's not all. What you eat will have an effect on the production of new neuronsin the hippocampus. So here we have a sample of diet -- of nutrients that have been shownto have efficacy. And I'm just goingto point a few out to you: Calorie restriction of 20 to 30 percentwill increase neurogenesis. Intermittent fasting --spacing the time between your meals -- will increase neurogenesis. Intake of flavonoids, which are containedin dark chocolate or blueberries, will increase neurogenesis. Omega-3 fatty acids, present in fatty fish, like salmon, will increase the productionof these new neurons. 

Conversely, a diet richin high saturated fat will have a negative impacton neurogenesis. Ethanol -- intake of alcohol --will decrease neurogenesis. However, not everything is lost; resveratrol, which iscontained in red wine, has been shown to promotethe survival of these new neurons. So next time you are at a dinner party, you might want to reach for this possibly"neurogenesis-neutral" drink. (Laughter) And then finally,let me point out the last one -- a quirky one. So Japanese groups are fascinatedwith food textures, and they have shown that actuallysoft diet impairs neurogenesis, as opposed to food that requiresmastication -- chewing -- or crunchy food. 

So all of this data, where we need to lookat the cellular level, has been generated using animal models. But this diet has also been givento human participants, and what we could see is thatthe diet modulates memory and mood in the same directionas it modulates neurogenesis, such as: calorie restrictionwill improve memory capacity, whereas a high-fat diet will exacerbatesymptoms of depression -- as opposed to omega-3 fatty acids,which increase neurogenesis, and also help to decreasethe symptoms of depression. So we think that the effect of diet on mental health, on memory and mood, is actually mediated by the productionof the new neurons in the hippocampus.

 And it's not only what you eat, but it's also the textureof the food, when you eat it and how much of it you eat. On our side -- neuroscientistsinterested in neurogenesis -- we need to understand betterthe function of these new neurons, and how we can control their survivaland their production. We also need to find a way to protectthe neurogenesis of Robert's patients. And on your side -- I leave you in chargeof your neurogenesis. Thank you. (Applause) Margaret Heffernan:Fantastic research, Sandrine. Now, I told you you changed my life -- I now eat a lot of blueberries. Sandrine Thuret: Very good. MH: I'm really interestedin the running thing. 

Do I have to run? Or is it really justabout aerobic exercise, getting oxygen to the brain? Could it be any kind of vigorous exercise? ST: So for the moment, we can't really sayif it's just the running itself, but we think that anything that indeedwill increase the production -- or moving the blood flow to the brain, should be beneficial. MH: So I don't have to geta running wheel in my office? ST: No, you don't! MH: Oh, what a relief! That's wonderful.