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Biology 202
2002 First Paper
On Serendip

Lets all go for a run! ----Does exercise really help the brain?

Rebecca Roth

Should I go run a marathon, join a yoga class, or head off to the gym? Is it really worth the time and effort? Afterall, sitting down and watching television can seem just as appealing. Why even bother working out? The reasons to work out may be greater than you think. Physical activity can make you feel good, keep you in shape, keep you healthy, but now researchers also are finding biological evidence that exercise benefits specific brain mechanisms. Just as exercise improves muscle tone and function, it may also have similar effects on the brain.

Some people have thought that exercise positively affects the brain as well as the body. Preliminary evidence suggests that physically active people have lower rates of anxiety and depression than sedentary people do (2). It seems logical that an active lifestyle would help the brain. However, the scientific observations were lacking. Now several biological studies indicate that working out does benefit the brain. This new insight may point more towards the notion that exercise has overall health benefits and also may lead to specialized physical activity programs for patients (1). Exercise may improve mental health by helping the brain cope better with stress, according to research into the effect of exercise on neurochemicals involved in the body's stress response (2). These findings come from animal as well as human studies and are leading to a better understanding of the overall health rewards of exercise and heightened support for exercise regimens that could aid recovery from a wide range of illnesses. Furthermore, the ongoing research indicates that specialized exercise regimens may help repair damaged or aged brains (1).

Some research suggests that exercise positively affects the hippocampus. The hippocampus is vital for memory and learning. Studies with animals found that exercise increases brain concentrations of norepinephrine in brain regions involved in the body's stress response (2). In a recent study, researchers found that adult mice doubled their number of new brain cells in the hippocampus when they had access to running wheels (1). The fact that the adult brain can increase its number of brain cells is amazing. It was once thought that the brain stopped producing new brain cells early in its development and that brainpower dimmed as cells died over the years. But in the past decade, researchers have found evidence that the brain continues to generate new brain cells throughout life, even in humans. Studies indicated that challenging environments, which included a number of components, such as pumped-up learning opportunities, social interactions and physical activities, were key to boosting the growth (1).

In another study, scientists found that voluntary physical activity alone was enough to trigger a boost in brain cell proliferation in rats. However, this proliferation was seen in relation to the running wheel. Swimming produced no change in mice and rats. This could be because they had access to a pool for only a brief amount of time per day. The runners had round-the-clock wheel access. It's also possible that the rodents don't enjoy swimming and it causes a stress to their systems that counters any benefit. Researchers believe that rodents enjoyed the running wheel because they will voluntarily go on it. Mice will log some 20,000 to 40,000 revolutions or four to six miles per day (1).

Scientists are trying to map the biological steps that induce the brain cell proliferation in the running rodents. One factor in the growth phenomenon may be brain-derived neurotrophic factor, which supports the function and survival of brain cells. The factor increased in the hippocampi of rats that voluntarily exercised on running wheels, according to an earlier report. In addition, scientists are studying whether exercise alters the molecular mechanisms that are important for learning and memory (1). It seems possibly plausible, since the cell research shows that changes occur in the brain's learning and memory center. In addition, past behavioral research on mice indicated that treadmill running improved certain learning and memory tasks. Even members of a family of mice that were poor learners improved their performances on the tasks. The exercise also prevented an age-related decline in mouse performance (1).

Researchers also are finding biological evidence that exercise can help the brain on other fronts. For example, animal studies are determining that exercise prevents the negative effects of chronic stress on the brain at the molecular level and boosts the brain's biological battle against infection (1).

There was another study on rats, this time comparing exercise, to the antidepressant drug imipramine. It was found that unforced exercise provided more benefits than either imipramine or forced exercise. Researchers induced a depression like condition in rats using the drug clomipramine. The rats showed several behavioral signs of depression, including an impaired sex drive. Researchers then gave one group of rats 24-hour access to a running-wheel for 12 weeks. Another group ran on a treadmill for an hour a day, six days a week for 12 weeks. A third group received imipramine for the last six days of the 12 week experimental period. And a fourth group remained sedentary and received no treatment for the 12 weeks. The rats given imipramine showed an increase in brain concentrations of norepinephrine, an increase in serotonin metabolism, another neurotransmitter associated with depression, and a decrease in the density of beta receptors, the brain cell receptors that norepinephrine attaches to. Both exercise groups also showed these changes. But only the wheel running rats saw increased sexual activity, the behavioral measure that was used to rate depression (2). This study showed that all exercise is not equal. It might not be exactly fitness that provokes neurochemical benefits. According to this study, the treadmill trained rats exercised more and became more physically fit than wheel running rats. However, the wheel runners received the biggest behavioral boost as measured by increased sexual activity. Some say research in humans finds a similar trend. Does this mean that the real benefit of exercising comes from a combination of biological as well as social factors?

Biologically, exercise seems to give the body a chance to practice dealing with stress. It forces the body's physiological systems, which are involved in the stress response to communicate much more closely than usual. The cardiovascular system communicates with the renal system, which communicates with the muscular system. And all of these are controlled by the central and sympathetic nervous systems, which also must communicate with each other. This workout of the body's communication system may be the true value of exercise (2).

Running can promote brain cell survival in animals with neurodegenerative disease. Previous work had indicated that running can boost brain cell growth in normal mice. In the new study, however, scientists studied mice with a condition similar to the disorder ataxia-telangiectasia (A-T), which in humans leads to a loss of motor control that typically leaves patients wheelchair bound. The A-T mice that ran were found to exhibit higher levels of cell survival than did their non-running counterparts. In sedentary A-T mice it appears that most newly born brain cells die. Running appears to ‘rescue’ many of these cells that would otherwise die (8). This study suggests that staying active may help delay progression of neurodegenerative conditions. Hopefully, further investigation will reveal exactly how exercise helps brain cells to survive.

Previous research suggests that maintaining a healthy flow of blood and oxygen protects the brain. Running may in fact give the brain a workout. A new study found that individuals consistently scored higher on intellectual tests after embarking on a running program. Seniors at Duke University started a 4-month exercise program. These seniors showed significant improvement in memory and other mental skills, also known as cognitive function. After 12 weeks of jogging, scores on complex computer based tests ''significantly increased''. These tests showed that joggers had a clear improvement in prefrontal function and that scores began to fall again if participants stopped their running routine (3). If exercise can help young people improve their cognitive ability, why not try it for the elderly?

Researchers at Southwestern Medical School gave a group of people two computer-based tests. Then the participants ran for half an hour on a treadmill. Once their heart rates were back to normal, the subjects were hooked up to an electroencephalogram (EEG) machine that reads brain activity and were given the two tests again. After exercise, the participants were able to make quicker decisions when taking the tests, particularly with the more difficult tests. The EEG machine reported that brain activity increased more rapidly (6).

It is important that we expand on these studies so that we can learn exactly how exercise affects the brain. Overall these group of studies are suggesting that an active lifestyle plays an important role in maintaining the function of the brain. If exercise improves mood, it follows naturally that it would improve the thinking process. Most people cannot think their best when they are depressed (4). Chronic physical inactivity can break down the body and its systems (5). I think the study that shows that mice didn't experience an age related decline in performance must be investigated thoroughly (1). If this observation turns out to be true for humans it can be of great benefit in preventing or at least slowing down the effects of dementia and Alzheimer’s disease. With the aging of our population, more people are developing these mentally debilitating diseases. Although exercise cannot prevent dementia, if we can just find a specific exercise regimen that would halt or reduce the decline of mental impairment it would be a terrific breakthrough.

Further studies are needed to explain specific mental processes that are improved by exercise and to better understand the underlying mechanisms of these improvements. Afterall, science just works as a summary of observations and is always subject to challenges based on new observations. That is what is so fascinating about scientific research.

References

1)Exercise and the Brain, Society For Neuroscience

2)Exercise Fuels the Brain's Stress Buffers,American Psychological Association

3)Jogging May Make You Smarter, Study Says , Reuters Health

4)Running increases cell proliferation and neurogenesis in the adult mouse dentate gyrus , National Neuroscience 1999 Mar; 2(3):266-70

5)Mental exercise keeps the brain in motion, Canadian Press News Article, Health News, Tuesday, May 18, 1999

6)Exercise and Your Brain , Southwestern Medical Center

7)Exercise 'could halt mental decline' , BBC News, Tuesday, 16 January, 2001

8)Exercise For Your Brain's Sake , Scientific American News




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