As far back as the Greeks and Romans, humans have documented the belief that there is a strong link between exercise and intelligence. But in the last two decades, neuroscience has begun to catch up with Thales and Juvenal's idea that a sound mind flourishes in a healthy body. While the studies unite in telling us that running will makes us smarter, it is only partly true.
The process is more complicated and reveals more about the wonderful complexities of both the human body and its evolution. Although the science might be helping us to understand how the mechanisms work, an important question remains: why does running make us smarter?
Two studies, one published by Finnish researchers in February and the other in Cell Metabolism in June, have expanded our understanding of the mechanisms involved in running and the ways that it enhances memory and cognition. Before these, it was understood that exercise induced a process called neurogenesis (where new brain cells are created) in a part of the brain involved in memory formation and spatial navigation, known as the hippocampus.
While intense exercise will create brain cells, they are basically stem cells waiting to be put to use. Exercise doesn't create new knowledge; rather, it gives you the mental equivalent of a sharpened pencil and clean sheet of paper. It prepares you for learning, but you have to actively do some learning yourself, too. Integrating exercise into your working or studying day would seem like a sensible option, if this particular benefit is of interest to you.
What the new research tells us is that it is not just any exercise that will create new brain cells for you. In the study by Finnish researchers, they discovered that only certain kinds of exercise are likely to result in the growth of new brain cells in adults.
According to the researchers, the exercise needs to be "aerobic and sustained". But they also looked at the neurobiological effects of the currently popular "high intensity interval training" (HIT), as well as resistance training (weightlifting). While the team discovered a minor response after HIT there was no response at all after the resistance training. So HIT will have a small impact on cognitive abilities, while weightlifting, it seems, will definitely not make you smarter. (The weightlifters have Arnold Schwarzenegger in their camp. Runners have the mathematical genius capable of running a marathon in 2.4 hours, Alan Turing, in theirs. As a committed distance runner, I'm saying nothing ...)
Since the 1990s, it has been understood that exercise also assists in learning because the activity produces a protein called brain-derived neurotrophic factor (BDNF). BDNF promotes the growth of new neurons and supports existing ones. John Ratey, a Harvard professor of psychiatry, called it "Miracle-Gro for the brain".
The Cell Metabolism study examined Cathepsin B (CTSB) protein secretion during running. By assisting in the expression of BDNF, this protein had beneficial effects on cognition, specifically enhanced adult brain cell growth in the hippocampus and spatial memory function.
The science is just settling into its pace and I am sure that in the next few years more and more research will appear to make sense of our deep love for this most simple and natural form of exercise. But there's still that question: why does the body need to reward us with greater cognitive function and more effective spatial memory and awareness just because we run?
I think the answer is to be found in natural selection. We have not evolved to be healthy, or to have a nice experience on this earth. Evolution is only really interested in the human body staying alive long enough to procreate. From that point on, natural selection is more or less disinterested in our well-being. When we look at these cognitive rewards in this way what do they tell us about ourselves and the human body?
Outrunning your knowledge
The human body has been around for about 2m years, and only in the last few thousand of these have we become literate - map-makers that can walk, make notes, and record journeys. For most of our history we have not had the technology that allows us to outsource this heavy cognitive work to a piece of paper, or a GPS.
As a child, the 19th-century poet, John Clare, desired to walk to the edge of the horizon to find new worlds beyond. He wanted, he said, to walk all the way out of his knowledge. I think that what these discoveries about running and improving cognitive abilities tell us is that the hunter-gatherers of prehistory had to have the ability to outrun theirs.
The many tweaks to the human body that make it possible for us to run for 10km on a hot day (standing on two feet, with the ability to sweat to keep cool) mean that even though we are slow in a sprint, we can chase down almost any animal on the planet to the point of exhaustion over longer distances. This is called persistence hunting, and it was a risky activity because it required hunters to leave behind the places they knew in the determined pursuit of prey. With no map-making technologies, the navigational skills of the brain had to step up and do all the work. So those people who adapted this brain cell growth response to distance running were more likely to find their way back to their tribe, and consequently, to survive.
The growth of new brain cells in the hippocampus and the enhancement of spatial memory that is brought on by endurance running is basically an evolutionary safety net for when you have outrun your knowledge, when you have run so far that you no longer know where you are and you need to learn, fast. It is a mechanism that makes information uptake easiest when historically you might have been tired, lost, and at your most vulnerable.
So lace up, step out the door, and prepare yourself for the rewards of an out of knowledge experience.