How about stress? Yes, stress will decrease the production of new neurons in the hippocampus.
How about sleep deprivations? Indeed, it will decrease neurogenesis.
How about sex? Oh, wow! Yes, you are right, it will increase the production of new neurons. However, it’s all about balance here. We don’t want to fall in a situation — about too much sex leading to sleep deprivations.
How about getting older? So the neurogenesis rate will decrease as we get older, but this 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 environment can have an impact on the production of new neurons. And here you see a section of the hippocampus of a mouse that had no running wheel in its cage. And the little black dots you see are actually newborn neurons-to-be. And now, you see a section of the hippocampus of a mouse that had a running wheel in its cage. So you see the massive increase of the black dots representing the 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 neurons in the hippocampus. So here we have a sample of diet — of nutrients that have been shown to have efficacy. And I’m just going to point a few out to you: Calorie restriction of 20% to 30% will increase neurogenesis. Intermittent fasting — spacing the time between your meals — will increase neurogenesis. Intake of flavonoids, which are contained in dark chocolate or blueberries, will increase neurogenesis. Omega-3 fatty acids, present in fatty fish, like salmon, will increase the production of these new neurons.
Conversely, a diet rich in high saturated fat will have a negative impact on neurogenesis. Ethanol — intake of alcohol — will decrease neurogenesis. However, not everything is lost; resveratrol, which is contained in red wine, has been shown to promote the 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.
And then finally, let me point out the last one — a quirky one. So Japanese groups are fascinated with food textures, and they have shown that actually soft diet impairs neurogenesis, as opposed to food that requires mastication — chewing — or crunchy food.
So all of this data, where we need to look at the cellular level, has been generated using animal models. But this diet has also been given to human participants, and what we could see is that the diet modulates memory and mood in the same direction as it modulates neurogenesis, such as: calorie restriction will improve memory capacity, whereas a high-fat diet will exacerbate symptoms of depression — as opposed to omega-3 fatty acids, which increase neurogenesis, and also help to decrease the symptoms of depression. So we think that the effect of diet on mental health, on memory and mood, is actually mediated by the production of the new neurons in the hippocampus. And it’s not only what you eat, but it’s also the texture of the food, when you eat it and how much of it you eat.
On our side — neuroscientists interested in neurogenesis — we need to understand better the function of these new neurons, and how we can control their survival and their production. We also need to find a way how to protect the neurogenesis of Robert’s patients. And on your side — I leave you in charge of your neurogenesis.
Margaret Heffernan: Fantastic research, Sandrine. Now, I told you, you changed my life — I now eat a lot of blueberries.
Sandrine Thuret: Very good.
Margaret Heffernan: I’m really interested in the running thing. Do I have to run? Or is it really just about aerobic exercise, getting oxygen to the brain? Could it be any kind of vigorous exercise?
Sandrine Thuret: So for the moment, we can’t really say if it’s just the running itself, but we think that anything that indeed will increase the production — or moving the blood flow to the brain, should be beneficial.
Margaret Heffernan: So I don’t have to get a running wheel in my office?
Sandrine Thuret: No, you don’t!
Margaret Heffernan: Oh, what a relief! Okay, that’s wonderful. Sandrine Thuret, thank you so much.
Sandrine Thuret: Thank you, Margaret.