It should come as no surprise that exercise is good for your health; however, evidence from the past decade has shown that physical exercise may actually increase brain power as well. This link between fit bodies and fit minds has led to exciting implications about the potential of behavior to influence brain function.
In June of 2010, the American College of Sport Medicine issued a press release on the results of a study involving 266 college students which showed that students who exercised more had higher GPA’s. The study found that students with a GPA of 3.5 or higher were 4 times more likely to take part in vigorous physical exercise than students with a GPA lower than 3.0. Even after controlling for confounding variables such as gender and major, researchers found that students who exercised vigorously for 20 minutes, 7 days a week had GPA’s that were, on average, 0.4 points higher than students who were sedentary – even if they studied for the same amount of time.
Based on these results, the researchers were able to generate a formula to give a rough prediction of a student’s GPA based on variables including the amount of time he or she exercised. The study also suggested that students who were more physically active were also more dedicated to their studies. Students who studied more than 3 hours per day were 4 times more likely to engage in vigorous physical activity than students who studied 1 hour per day1. And healthy young college students are not the only ones who stand to benefit from research in this field.
Exercise and the aging brain
At the University of Illinois, it was found that when a group of elderly people followed an exercise regimen of walking 3 times a week, MRI scans showed growth in many areas of the brain. Thus, a little exercise was able to produce visible improvements in these patients. And the more the better: those who had the most mental improvement were those with a higher VO2 max – an indication of physical fitness in terms of how much oxygen patients consumed while exercising. So, older adults who want to keep their wits about them into their golden years would do well to take up some light jogging or aerobics, and it’s never too late to start. Even adults who had led sedentary lifestyles were able to expand their mental capacities and restore lost brain volume by engaging in moderate exercise. Many studies conducted among the elderly support these findings and have shown that adults who are physically active have better memories and are able to perform better on tests of mental function as they age2.
More than just surveys
With the accumulation of evidence from surveys such as these, a causal explanation is rather appealing. After all, the results regarding college students seem to be in agreement with the common experience that students who are physically fit tend to have lower stress levels and an improved sense of well-being in general that is highly conducive to academic success. However, correlation does not prove causation, and as encouraging as they are, the correlations between exercise and mental function can be easily subject to alternative explanations. For example, one cannot eliminate the possibility that students who exercise more may simply exhibit superior self-discipline and thus, are able to study more diligently. Then the results of the study from the American College of Sports Medicine could be construed to be a study showing a link between self-discipline and GPA. Therefore, exercise may indeed be recommendable for health reasons, but such surveys may not be convincing enough to persuade students to try boosting their grade point averages by hopping on the treadmill.
However, a compelling body of evidence from the past several years has established a strong biochemical link between physical activity and the brain. In the lab of Dr. Fred Gage at the Salk Institute, studies led by Dr. Henriette Van Praag have found convincing evidence that physical activity can augment the birth of new brain cells and improve learning and memory in mice.
Shiny new brain cells
It has only just begun to enter the realm of common knowledge that, contrary to what was previously thought, brain cells grow throughout adult life. In fact, new neurons are being born every day. This birth of newborn brain cells, termed “neurogenesis,” takes place in only two areas of the brain. One of those areas is the dentate gyrus – a particular group of brain cells in the hippocampus that plays a role in learning and memory. In order to distinguish new cells from old ones, mice were injected with a nucleic acid analog, BrdU, which could be incorporated into newly dividing cells and used to identify cells that were the products of adult neurogenesis. Cells that were newly born in the adult brains glowed when stained with a particular chemical that detects this analog.
“What’s amazing about neurogenesis is that, in most parts of the brain, no new neurons are made after you are born. But in the hippocampus, more neurons are born almost every day,” says Chunmei Zhao, a member of the team in Dr. Gage’s lab studying this phenomenon.
As one would expect, researchers in the Gage lab found that mice whose brains glowed with new cells due to higher rates of neurogenesis performed better on tests of cognitive function.
Mazes and memory
In the Gage lab, mice were engineered such that the injection of a chemical could inhibit the generation of new brain cells. These mice were then subjected to tests of learning and memory to affirm the link between these new brain cells and brain function.
In the Morris water maze test, the mice are put in a pool of milky water with some platforms just under the surface so the mice cannot see them. As it turns out, mice do not like water; in order to get out, they have swim around to find out where the platform is. When they are put back in the same pool later, mice show they have learned by finding the platform more quickly. Mice in which neurogenesis had been inhibited were less able to learn where the platform was, spending more time swimming around randomly even though they had been placed in the exact same situation a few times before.
In addition to the water maze test, mice in this experiment were subjected to a test of mental function called “contextual fear extinction.” In this test, mice are put in a particular environment with certain markers. Then they are given a shock so that they will learn to associate that environment with fear, causing them to freeze when placed there. Mice with poorer memories do not learn to exhibit this freezing behavior as quickly as mice with better memories – that is, they are worse at remembering what happened to them the last time they were in a given environment. This is exactly what happened with the inhibited mice. Unable to grow new brain cells, mice showed less fear of places they should associate with pain. The findings of these tests have been reproduced in other labs, serving as strong evidence to support a role for neurogenesis in learning and memory.
Running and neurogenesis
In 1999, the Gage lab found that, compared to mice that were sedentary, mice that exercised voluntarily by running on a wheel had at least twice as many surviving newborn neurons as did mice who did not have the option of exercising. The area of their brains responsible for learning and memory was growing in response to the aerobic exercise.
In order to reinforce the connection between exercise, neurogenesis, and the “intelligence” of a mouse, the mice in the study also took the Morris water maze test. Mice that were in the running group significantly outperformed their peers – even mice that were supposed to exercise by swimming. Thus, the same group of mice that showed a higher rate of newborn brain cell growth also showed improved ability to learn and remember.
“And the best thing is, it’s never too late to exercise,” says Dr. Zhao, “even in old mice you can still see a very pronounced effect.”
The size of the hippocampus and the rates of neurogenesis decline with aging; however, these dimensions can actually be rescued by voluntary running. Another experiment led by Dr. Van Praag in 2005 found that, in aged mice which had led sedentary lifestyles and exhibited this decline, neurogenesis could be restored to 50% of the levels that young exercising mice showed. Thus, exercise not only improves neurogenesis over the course of a lifetime but is capable of rescuing neurons from decline – partially restoring the minds of aged mice to a younger, fitter time in the timeline of their mouse lives.
But does this work for humans?
Since these landmark studies in mice, more work has been done to find evidence that exercise increases neurogenesis and brain function in living humans. In 2007, a collaboration between the Gage lab and the lab of Dr. Scott Small of Columbia University found that, in a group of people aged 21 to 45 who exercised for 12 weeks, subjects who exercised performed better on a variety of tests of mental agility. MRI scans of the brains of these same patients showed that blood flow increased in the dentate gyrus specifically – the very same region where new brain cells are born. Furthermore, autopsies of patients showed that there were higher rates of neurogenesis in patients who increased blood flow to this region through exercise. Thus, researchers have found evidence that the connection between exercise, neurogenesis, and brain power may apply to a living, breathing human being just as it applies to mice.
“Adult neurogenesis was initially thought of as way in which the brain may be able to repair itself after disease or injury,” says Dr. van Praag, now with the National Institute on Aging. “There is now both correlative and causal evidence [that] exercise enhances neurogenesis and is correlated with improved performance on both general hippocampus dependent tasks (maze learning) and tests tailored more specifically to test the function of the dentate gyrus (spatial pattern separation learning).”
Researchers continue to conduct more experiments in order to refine the biological connection between physical and mental fitness. Scientists still do not know for sure what exactly it is about running that can cause newborn brain cells to grow in the adult hippocampus. It is not known whether the effects are simply due to increased rate of blood flow, the growth of new blood vessels, or the generation of molecules during exercise that have a particular effect on the adult brain.
“All those factors may play a role. We are looking for the trigger in the periphery (muscle),” says Dr. van Praag, referring to her recent research in which the injection of endurance factors enhanced cognition and elevated adult neurogenesis in the dentate gyrus of mice.
All in all, the evidence that we have so far is rather encouraging: it does indeed seem that exercise is good for your brain.
“For the general population, the research may give another reason to exercise,” adds Dr. van Praag, “I exercise more myself, though I was always rather into sports.”
So for students, exercise may be as much a part of preparing for that midterm as working on problem sets; for older adults who want to keep their minds from slowing down, going for a run may be as helpful as buying a fancy memory game. In the end, the phenomenon of neurogenesis brings us back to the core idea that our behavior, what we do on a daily basis, can have a tangible, biological effect on the development of our minds. Now that’s something to think about.
WRITTEN BY ANELAH MCGINNESS. Anelah McGinness is a Physiology and Neuroscience major, pursuing minors in Spanish Literature and Health Care/Social issues from Revelle College. She will graduate in 2013.
Parker-Pope, T. (2010, June 3). Vigorous exercise linked with better grades. New York Times.
Hertzog, C., Kramer, A. F., Wilson, R. S., Lindenberger, U. (2009). Fit body, fit mind. Scientific American, 20(4), 24-31.
C. Zhao, personal communication, 2011.
Deng, W., Saxe, M.D., Gallina, I. S., Gage, F. H. (2009, October 28). Adult-born hippocampal dentate granule cells undergoing maturation modulate learning and memory in the brain. J Neurosci, 29(43), 13532-42.
Van Praag, H., Christie, B. R., Sejnowski, T. J., Gage, F. H. (1999, November 9). Running enhances neurogenesis, learning, and long-term potentiation in mice. Proc Natl Acad Sci U S A, 96(23), 13427-31.
Van Praag, H., Kempermann, G., Gage, F. H. (1999, March). Running increases cell proliferation and neurogenesis in the adult mouse dentate gyrus. Nat Neurosci, 2(3), 266-70.