Less recognized in the public eye is the role that exercise plays in neurogenesis. It is possible that the relationship between physical activity and brain health may be even more important than brain health and mental games. Using sophisticated technologies to examine the workings of individual neurons – and the makeup of brain matter itself – scientists in just the past few months have discovered that exercise appears to build a brain that resists physical shrinkage and enhances cognitive flexibility. Exercise, the latest neuroscience suggests, might do more to bolster thinking than thinking itself. Why would exercise build brainpower in ways that thinking might not? The brain, like all muscles and organs, is a tissue, and its function declines with underuse and age. Beginning in our late 20s, most of us will lose about 1 percent annually of the volume of the hippocampus, a key part of the brain related to memory and certain types of learning. Exercise appears to slow or reverse the brain’s physical decay, similar to way it affects muscles. Although scientists thought until recently that humans were born with a certain number of brain cells and would never generate more, we now know that the creation of new brain cells occurs on a regular basis – primarily in the hippocampus. And what spurs neurogenesis? Exercise does. Studies on mice and rats that ran for a few weeks generally had about twice as many new neurons in their hippocampi as sedentary animals.
What is more important than the formation of new neurons is that they join existing neural networks. Without this, the development of new neurons does not improve intellect. One way to pull neurons into the network is to learn something. However, neurons that join an existing neural network through the process of learning something new appear to be active only when executing the newly learned task. For example, neurons formed through the process of learning French will only be active when speaking or reading the new language. Exercise, on the other hand, appears to render new neurons nimble. Rats and mice that ran had newly formed neurons that fired not only when running, but when cognitive skills like exploring unfamiliar environments were practiced. Although we do not completely understand how exercise changes the brain, research suggests that exercise increases a substance in the brain called brain-derived neurotropic factor (BDNF) – which strengthens cells and axons, fortifies the connections among neurons, and elicits neurogenesis. People display higher BDNF levels in their bloodstreams after a bout of exercise. BDNF is probably not the whole story – a recently study on elderly mice found that 117 genes were expressed differently in the brains of the group that began a program of running, compared with those that remained sedentary. It is worth noting that scientists were only looking at a small portion of the many genes that might be expressed differently in the brain by exercise. We do not know exactly what type of exercise protocol works best to create neurogenesis. A limited number of studies done recently have demonstrated cognitive benefits among older individuals who lifted weights for a year but did not engage in other forms of exercise. However, all animal studies to date have focused on aerobic activities. Whatever the activity, the science is clear that the exercise does not need to be exhausting to be beneficial for the brain. When a group of 120 older men and women were assigned to walking or stretching programs for a major study in 2011, the walkers ended up with larger hippocampi after one year. The stretching group, however, lost brain volume to normal atrophy. The walkers also displayed higher levels of BDNF in their bloodstreams and, not surprisingly, performed better on cognitive tests. The improvement translated into regaining two or more years of hippocampal youth. Combining both mental focus and repetitive exercise movements is better than one or the other. Dr. John Ratey writes in Spark: The Revolutionary New Science of Exercise and the Brain that BDNF levels increase the most with forms of exercise that tax the body and the cognitive system simultaneously – dancing, yoga, and perfecting your weight training technique will all create more complex synaptic connections than walking or running alone. Have a great workout! References Doidge, Norman (2007). The Brain That Changes Itself. New York, New York: Penguin. Ratey, John (2008). Spark: The Revolutionary New Science of Exercise and the Brain. New York, New York: Little, Brown and Company Reynolds, Gretchen. How Exercise Could Lead to a Better Brain. New York Times Online Edition, April 18 2012.