Exercise helps you make more brain cells
In the article about exercise improving your cardiovascular system I told you that thousands of your brain cells die every day because they don’t the get the oxygen and nutrients they need to stay alive. What I haven’t told you is that your brain can potentially make thousands of new neurons every day, a process called neurogenesis, to replace the ones that die. I’ll bet you didn’t know that your brain makes thousands of new brain cells every day throughout your entire life. It’s true! Way back in 1962 an MIT scientist named Joseph Altman published this truly groundbreaking article in the journal Science showing what he believed be newly-formed neurons in adult rats. Until that point it was assumed that new neurons were only made in the early stages of a young mammal’s life. However, his work wasn’t looked at too seriously at the time, and it took until the 1990s before scientists really began looking into this area of research again. Since then Altman’s work has been shown to be completely true – even eldery adult mammals produce new neurons every day1! And these newly-formed neurons migrate and are incorporated into different areas of your existing network of brain cells. So the saying “You can’t teach an old dog new tricks” can finally be laid to rest because it’s a bunch of hogwash. The only catch is that not all of these new neurons survive. In fact, the majority of them die within the first week. But, there is something you can do to increase the number of new neurons being produced by your brain and also keep them alive. You guessed it – exercise! Let me tell you a story about some mice:
A Mouse Tale:
A clever group of scientists decided they were going to figure out if they could boost the number of neurons animals’ brains produce. They divided mice into 5 groups – normal, swimmers, learners, enriched, and runners. The normal group was just stuck in a plain cage. The swimmers were also stuck in a plain cage, but they got to swim around every day for a little while. The learners were taught how to navigate a water maze. The enriched group got to live in a swank cage with tubes and toys and a bunch of friends. And the runners got the same swank cage with their friends but also a running wheel. The mice in all the groups went about their daily mouse business, chilling with their mouse friends, but they discovered that the mice in the cage with the running wheel would run an average of 3 miles per day. I guess when you’re a mouse with nothing to do you might as well tick off a few miles on the old wheel. After a few weeks of living in these different environments all 5 groups of mice had the number of new neurons formed in their brains counted. And guess what – the mice with the running wheel had 200% more, or 3 times the number of, new neurons than any of the other groups2. This means that for every 100 new neurons the mice who were just chilling, swimming or learning with their friends generated, the running group had 300! That sounds like 3 times the brainpower boost to me!
So why does exercise cause your brain to make new neurons? Pretty much the same reason working out your muscles causes them to get bigger and generate more muscle tissue – exercise boosts the level of growth molecules in your body, which tells your brain to make more neurons and preserve the ones you already have. One of the most important brain cell growth molecules is called Brain-Derived Neurotrophic Factor, or BDNF for short. It’s name tells what it is: Brain-Derived means it’s generated mostly in the brain, Neurotrophic means it tells your body to grow more neurons, and Factor means just that – it’s one of many factors contributing to brain cell growth. When you exercise the levels of BDNF in your brain skyrocket3 and that’s why exercisers produce 3 times the number of new brain cells than their sedentary counterparts.
You might be thinking “Yeah, but Joe the Tutor, these are mice not humans.” But what holds true for one mammal usually holds true for others, and we can’t do these experiments on humans because they involve dissecting brains! But consider this: Just a decade ago no one thought that the human brain makes new neurons in old age, but then it was discovered that rats do4, and then it was discovered that guinea pigs do5, and then in monkeys6, and finally because of generous organ donors, in humans1. This means that cardiovascular exercise dramatically increases the number of new brain cells created in your very own brain! This process of producing new neurons, called neurogenesis, has more of an impact on your cognition the older you get since the number of neurons continues to add up over time. Over a lifetime, an exerciser could have 10%-20% more brain cells than someone who didn’t exercise! The scientist who did the mice study went out and bought a pair of running shoes when the results came in. I would too!
But there are still two important questions to be answered: What do all these new neurons do once they are made? And do they make you smarter?
It turns out that indeed these newly-formed neurons are very important. They are formed in a part of the brain called the hippocampus (there’s a hippo running through campus in my brain?!). The hippocampus is one of the most important parts of the brain when it comes to learning and memory formation and it’s been shown that people who have damage to this area of the brain, or reduced neurogenesis, have a difficult time learning new information and are more susceptible to diseases like Alzheimer’s. The more new brain cells in the hippocampus the better! After the neurons are formed they migrate through your brain and are incorporated into your existing networks of brain cells7. Scientists have shown that these cells have very high plasticity, meaning they are extremely moldable and can change shape and function depending on what they are used for. And when these neurons incorporate into your existing networks of cells they connect to thousands of other neurons and strengthen your brain’s memory pathways. In particular, these new brain cells have enhanced long-term potentiation (LTP) abilities8 which, in lay man’s terms, means they can form new permanent memories more easily than old neurons. And best of all, these cells remain moldable for months9 just waiting for you to challenge them with some new information!
It’s just like if you’re remodeling an old house with a bunch of weak support beams and you put in some new, sturdy cross-members. The older a house gets, the weaker it becomes. Weather, mold, maybe some termites and rodents can all take a toll on the structural integrity of the house over the decades. The scariest part about an old house is the deterioration that you can’t see going on behind the walls. Your brain is the same way, you might not notice any defects until it’s too late. Without any maintenance or new materials added for support over the years you might even become afraid that the walls of the house are going to fall down – what a catastrophe! This would be like getting Alzheimer’s when you’re old, I can’t imagine a worse fate. Your brain does try to make new cells to keep your brain in good shape, but if you don’t use your brain or exercise they’ll disappear. It would be like going to Home Depot and buying a bunch of sturdy two-by-fours, plopping them down in your garage, and then never using them. Because the neurons formed by neurogenesis will stay alive and incorporate into your existing network of brain cells if you exercise, it’s like adding more structural support beams to your house every day, and 200% more of them!
Convinced yet? I hope so! But if for some reason you are still not convinced that you need to exercise to boost your brainpower (maybe you also think that science hasn’t proved the world is round?), I will be discussing all the fantastic details about the human studies of exercise’s impact on learning and memory.
So here’s the take-home message:
Your brain makes new neurons every day, a process called neurogenesis. Exercise sends out molecules that tell your brain to make more new neurons and keep them alive. These new cells integrate into your existing networks of brain cells and greatly improve your ability to learn and store new information. More new brain cells means you learn faster, remember more and are just plain smarter than before.
- Eriksson PS et al. Neurogenesis in the adult human hippocampus. Nature Medicine. 4:1313-1317. 1998.
- van Praag H, Kempermann G, Gage FH. Running increases cell proliferation and neurogenesis in the adult mouse dentate gyrus. Nature Neuroscience. 2:266-270. 1999.
- Neeper SA, Gómez-Pinilla F, Choi J, Cotman C. Exercise and brain neurotrophins. Nature. 373: 109. 1995
- Altman J, Das GD. Autoradiographic and histological evidence of postnatal hippocampal neurogenesis in rats. Journal of Comparative Neurology. 124:310-335. 1965.
- Altman J, Das GD. Postnatal neurogenesis in the guinea-pig. Nature. 214:1098-1101. 1967.
- Gould E et al. Proliferation of granule cell precursors in the dentate gyrus of adult monkeys is diminished by stress. Proceeding of the National Academy of Sciences. 95:3168-3171. 1998.
- Tashiro A et al. NMDA-receptor-mediated, cell-specific integration of new neurons in adult dentate gyrus. Nature. 442:929-933. 2006.
- Schmidt-Hieber C. Jonas P. Bischofberger J. Enhanced synaptic plasticity in newly generated ganule cells of the adult hippocampus. Nature. 429: 184-187. 2004.
- Zhao C. Teng EM. Summers Jr. RG. Ming GL, Gage FH. Distinct morphological stages of dentate granule neuron maturation in the adult mouse hippocampus. Journal of Neuroscience. 26. 3-11. 2006