Running Neurogenesis: Can You Grow New Brain Cells?
As runners, we may find ourselves wondering if there are any benefits that running does not provide. We know that it boosts our well-being by shrinking our waistlines and providing us with the feel-good chemical, dopamine. We know that it reduces stress by improving the quality of our sleep and lowering the amount of cortisol1 that is released into our blood stream. We also know that research suggests it decreases the risk of depression, heart attack, stroke, diabetes, and certain cancers. Recently, scientists have determined one more reason to run: aerobic exercise spurs neurogenesis, which is the growth of brain cells.
From the time we are born until the time of our death, the brain is continually changing. At birth, we have basic skills, reflexes, and all of the neurons (approximately 100 billion) that our brain will need for our entire lives. In the first two years of life, the brain undergoes numerous changes as a result of our environment; but, most notably, neurons grow larger and connections (called synapses) are made.
As we go through our formative years, from 5 – 12 years old, our brains determine which synapses are needed (i.e. which skills are reinforced most often), and which are not. The ones that are not necessary essentially die, leaving room for skills like language to flourish. In our teen years, our brain reaches its adult weight and we are now able to consider multiple ideas simultaneously.
Finally, once we reach our mid-20’s, our brain reaches peak performance, right after our frontal lobe (which is responsible for decision making, judgment, and planning) becomes fully developed. From this point forward, our brain begins to decline. First, we lose speed and spatial skills, then the number of neurons steadily decreases. Until now, this process, termed neurodegeneration, was thought to be irreversible.
In recent years, neurogenesis, or the generation of new neurons, has been a hot topic of study. Researchers believe that neurogenesis could be implicated in the treatment or reversal of neurological disorders and diseases, such as Alzheimer’s Disease, Parkinson’s Disease, or stroke, where irreparable neurodegeneration is a hallmark trait. Thanks to the BRAIN initiative put forth by President Obama, funding for neurological research is at an all time high.
One such study2, which was performed on adult mice, has spurred an entire body of reaches thanks to the amazing result that aerobic activity, such as running, can generate new neurons in certain parts of the brain. This is the first study that shows the regeneration of neurons in adults, which was once thought to be impossible.
In this experiment, adult mice were placed in one of five different environments: one where they learned to complete a maze, one where they were forced to swim, one where they voluntarily ran on a wheel, one where they lived in an enriched environment, and one where they lived a controlled environment. For the mice that ran voluntarily, the number of surviving newborn cells in their brains doubled, in a manner that was consistent with purposeful enrichment. The mice were presented with challenges aimed to stimulate their brains.
For the first time ever, a simple activity that is accessible to all able-bodied humans was shown to provide this powerful result.
It should be noted that aerobic exercise has not been shown to generate new neurons in every part of the brain. Instead, the hippocampus, namely the dentate gyrus, was shown to form new cells. The hippocampus is important for short and long-term memory, as well as spatial navigation. In addition, the hippocampus is connected to a number of neurological disorders, such as Alzheimer’s disease.
The hippocampus is the first region affected by the disease, and is the primary cause of memory loss and disorientation among sufferers. For people who suffer injury to the hippocampus, amnesia is common (i.e. the inability to develop and retain memories). The hippocampal area where the most neurogenesis was observed was the dentate gyrus. This compartment is believed to form new episodic memories. For this reason, researchers feel there is a strong connection between aerobic exercise, neurogenesis, and the fight against dementia and Alzheimer’s. For instance, when dentate gyrus function is impaired, memory loss, stress, depression, and poor navigational skills are the result. Until this study, the brain was thought to stop developing after the mid-20’s.
Photomicrographs in (a, b) show running mice have more dividing cells (BrdU+) than mice in the control group. Microscopy performed with immunofluorescent confocal (c, d) shows newly born neurons. Here, double-labeling for neuron proliferation (BrdU+) and a neuronal phenotype (NeuN+) is highlighted in orange. Source.
This seminal study was followed up by researchers at both Cambridge and the US National Institute on Aging who simplified the experiment by looking only at two groups of mice: those who were allowed to voluntarily run, and those who did not have free access to a wheel. Both groups of mice were also taught a task. They were shown two identical squares and if they nudged the proper square, a treat was presented. This task was repeated throughout the study3, in order to test the memory of each group of mice. The mice that ran (up to 15 miles per day!) performed significantly better than the mice who were relatively sedentary, which was supported by the fact that the mice in the running group had developed an average of 6,000 new brain cells per cubic centimeter of brain tissue in the dentate gyrus.
Does running have to be performed voluntarily to grow new brain cells?
Interestingly, neurogenesis was only observed in mice that exercised voluntarily. For instance, in the first study mentioned, the group of mice that were termed “swimmers” underwent forced exercise and did not display the same neurogenesis benefits. This opened the door to additional studies4 that sought to determine the reasoning behind this discovery. According to researchers from the China Medical University, running produces intracranial self-stimulation, meaning that the chemicals (i.e. dopamine) that are released as a result of running actually promote neurogenesis. Therefore, exercising voluntarily, as opposed to being or feeling forced, improves the growth of new neurons. In other words, choosing to run makes the brain feel good and feeling good promotes neural growth. Interestingly, the only other activity shown to affect the brain in a similar manner, via intracranial self-stimulation, is sexual activity.
In addition to these studies, there are a number of other reasons to believe that running can be beneficial in the growth of new grey matter. For instance, endorphins are important for suppressing cortisol, the stress hormone that causes inflammation in the body, leading to a weakened immune system, high blood pressure, food cravings, and weight gain. Why is the suppression of cortisol important? Besides the fact that having less cortisol in your system makes you happier, cortisol has been linked5 to neurodegenerative diseases. Aerobic exercise has also been shown6 to increase important growth factors in the brain, such as brain-derived neurotrophic factor (BDNF) and glial cell line-derived trophic factor (GDNF), both believed to be responsible for stimulating the growth of new neurons. Other hormones, such as testosterone, are also produced as a by-product of vigorous activity and promote neural growth.
How does the brain of a mouse compare with that of a human?
Mice and men are surprisingly similar, from a hard-wiring standpoint. In fact, humans share 90% of the genes that are responsible for controlling the inner workings of the brain. The ways in which they differ are unlikely to contribute in a deleterious way to neurogenesis studies. This is also the reason why $100,000,000 has been pledged towards the further understanding of the mouse brain. The information that has been gained so far has been useful, and is expected to help better understand the mechanisms of human disease, as well as potential treatments.
For now, unfortunately, neurogenesis studies on humans are limited, given that we are not yet technologically advanced enough to study generations of new neurons on living patients. However, there have been a number of studies that correlate cardiovascular health in humans with important brain benefits which helps to solidify the findings from animal studies. For instance, this study7 discusses the role of cardiovascular fitness and the risk of developing early-onset dementia.
Participants who tested high for cardiovascular health when they were 18 year olds (via conscription records) were eight times less likely to have developed early onset dementia later in life. Scientists might suggest that the rates of neurogenesis from aerobic activities, such as running, helped ward off the neurodegeneration that leads to dementia.
There is another study9 that looked at 10 sets of twins in which one exercised on a weekly basis and the other one did not. Researchers found that the identical twins who exercised had less body fat, more endurance and more grey matter in their brains. The grey matter is the dark tissue that contains nerve cell bodies (neurons). Neurons are highly involved in mental processing – especially in those regions for motor control and coordination.
The Importance of Diet
This TED speech claims that in addition to running, there are a number of other ways to improve neurogenesis. A healthy diet is important; especially one that limits refined sugars and processed foods, and has an abundance of healthy fats. Particularly important fats include omega 3 fatty acids, as well as docosahexaenoic acid, both of which are found in fish. In addition to fats, foods that are high in antioxidants, such as blueberries, curcumerin, and green tea also support neurogenesis. Additional factors that promote the growth of new cells are meditation, exposure to sunlight, proper sleep, avoidance of drugs and alcohol, and a smaller waistline. Sandrine Thuret, the speaker from the above speech published a study which shows the impact of diet on adult hippocampal neurogenesis8.
Since runners typically live a lifestyle that embodies the above traits, it is no surprise that runners have been implicated by science as being among the healthiest demographic of people, with ever-increasing neural activity!
These findings are important because the new hippocampal neurons produced as a result of neurogenesis can help enhance our understanding of the human brain. Since these new neurons are essential for learning spatially and temporally complex tasks, sustained aerobic exercise can be the key to solving many brain-related issues.
Running can therefore help nurture human’s capacity to remain physically and mentally active and engaged in the world, even at advanced ages. On the same note, running can be the key to preventing Alzheimer’s disease, since the hippocampus is a part of the human brain that suffers the most damage in this dementia-related disease.
Filtering the above findings, it seems that no other type of exercise (such as resistance training or HIIT) can develop new brain cells.
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2. Henriette van Praag, Gerd Kempermann, 2 & Fred H. Gage, Running increases cell proliferation and neurogenesis in the adult mouse dentate gyrus, Nature Neuroscience 2, 266 – 270 (1999) doi:10.1038/6368 (link)
3. David J. Creer, Carola Romberg, Lisa M. Saksidab, Henriette van Praag, and Timothy J. Bussey, Running enhances spatial pattern separation in mice, doi: 10.1073/pnas.0911725107 PNAS February 2, 2010 vol. 107 no. 5 2367-2372 (link)
4. Takahashi T, Zhu Y, Hata T, Shimizu-Okabe C, Suzuki K, Nakahara D., Intracranial self-stimulation enhances neurogenesis in hippocampus of adult mice and rats., Neuroscience. 2009 Jan 23;158(2):402-11. doi: 10.1016/j.neuroscience.2008.10.048. Epub 2008 Nov 7. (link)
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7. Nyberg J, Åberg MA, Schiöler L, Nilsson M, Wallin A, Torén K, Kuhn HG., Cardiovascular and cognitive fitness at age 18 and risk of early-onset dementia, Brain. 2014 May;137(Pt 5):1514-23. doi: 10.1093/brain/awu041. Epub 2014 Mar 6. (link)
8. Stangl D, Thuret S. Impact of diet on adult hippocampal neurogenesis. Genes & Nutrition. 2009;4(4):271-282. doi:10.1007/s12263-009-0134-5. (link)
9. Rottensteiner M. et al. Physical activity, fitness, glucose homeostasis, and brain morphology in twins. Med. Sci. Sports Exerc. 47, 509–518 (2015) (link)