New Research Shows How Exercise Benefits the Brain

Charles Hillman, at the University of Illinois, took 259 third and fifth graders, measured their body-mass index, and then put them through some gymnastics routines. Afterwards, he checked the kids' physical abilities against their mental ones, testing them with math and verbal quizzes. Interestingly, the kids with the fittest bodies also scored highest on the quizzes.

Hillman's study, along with other recent studies, is showing that physical fitness is key to mental fitness. A recently published paper announced that, simply by engaging in a three-month exercise program, a group of study volunteers grew new nerve cells in their brains. Other researchers have discovered that vigorous exercise can induce older nerve cells to form dense interconnections within the brain, making it function faster and better. The evidence abounds that exercise is critical to preventing or delaying Alzheimer's disease and dementia.

It always made sense that exercise could delay the onset of age-related mental degeneration. After all, exercise allows the heart to pump more blood, which reaches the brain, supplying much needed oxygen. More oxygen means better nourished brain cells.

The understanding of how this nourishment occurs, however, is just now being elucidated. Biochemically speaking, it is being found that muscle contraction generates a molecule called IGF-I (or insulin-like growth factor I). Upon reaching the brain, IGF-I induces the releases of a second molecule, called BDNF (brain-derived neurotrophic factor). BDNF induces brain nerve cells to grow and branch out, leading to new nerve-to-nerve connections, the underlying process behind learning and higher thought.

Meanwhile, a brain that is low on BDNF starts to shut itself off to the accumulation and processing of new information. Fernando Gómez-Pinilla, at UCLA, placed two groups of rats on a wheel-running exercise routine. After two weeks, Gómez-Pinilla took the animals off of their exercise routine and injected half the number with a chemical that blocks BDNF. Then the whole group was subjected to the mental challenge of finding an object placed underwater. The group that was not BDNF-blocked easily pinpointed the location of the object; the BDNF-blocked group wasn't as lucky.

Humans, like rats, are also dependent upon BDNF for quick wit and efficient learning. BDNF levels stay rather constant throughout adulthood, but then start to drop off in old age, causing wide-spread nerve death and making memory and new learning difficult. Until recently, it was thought that new nerve cell growth, or "neurogenesis", could not happen past childhood, thus dooming people in old age to progressive mental degeneration. However, recent evidence suggests that this old assumption may not be true. Exercise, in particular, is being found as a root cause of neurogenesis beyond childhood. Last week, Columbia University and Salk Institute researchers published some unexpected findings in the journal Proceedings of the National Academy of Sciences. The researchers had human test subjects perform aerobic exercise for three months, and then measured the subjects for neural brain growth. Adults who had exercised, as opposed to those who had been sedentary, appeared to have grown completely new neurons.

Interestingly, the majority of new neurons showed up in a region of the brain called the dentate gyrus, a region of the hippocampus involved directly in memory and learning. The dentate gyrus has been found to be involved in such tasks as matching people's names to faces, one of the skills that decreases with increasing age. The hippocampus, luckily, is extremely responsive to BDNF. This has important implications for the aging brain, suggesting that exercise may not only slow down age-related dementia and forgetfulness, but possibly even reverse it.

Arthur Kramer, a psychologist at the University of Illinois, has recently discovered even more evidence of the benefits of exercise on the brain. Using MRI (magnetic resonance imaging) technology, Arthur found that several weeks of aerobic exercise performed by men and women in their 60s and 70s caused the frontal lobes of their brains to increase in size. Not only that, but right after performing an exercise regimen, the men and women could answer learning-based questions more accurately and quickly. This is certainly not due to neural growth, which can take weeks to occur. Rather, the brains of the men and women who exercised were probably responding to neurotransmitters and endorphins such as dopamine, serotonin, and norepinephrine, which are all found to increase after exercise.

However, the effects of exercise, whether on neurotransmitter and endorphin levels, or on neural growth, are transitory. Within a month of inactivity, "the astrocytes shrink down again, and then the neurons don't function as well anymore," says William Greenough, a psychologist at the University of Illinois. So, to keep reaping the benefits of exercise, one must continue to exercise.

Because exercise generates additional dopamine and serotonin, it can also act as a good antidepressant. Many antidepressant medications are based upon the slowing of the rate of serotonin or dopamine re-uptake (degradation) by the brain. If exercise can supply additional serotonin and dopamine, it may actually work as a more natural antidepressant, on a scale comparable to drug or psychological therapy.

Neural degeneration may also affect the onset of depression. Brain scans of patients with clinical depression showed that the hippocampus of these patients was reduced in size compared with their non-depressed controls. This makes sense when considering that the hippocampus, mentioned earlier, is involved in regulation of mood as well as memory. Based upon this finding, the beneficial effect of exercise on neural growth, and thus the alleviation of depression, is fairly obvious.

How much exercise should one do in order to reap the rewards of good mood and neural growth? The U.S. Centers for Disease Control and Prevention recommend that adults exercise for at least 30 minutes, five days a week, if the exercise is of a moderate intensity (any exercise you can perform while carrying on a conversation). Alternatively, adults may exercise for 20 minutes, three days a week, if the exercise is of a high intensity (any exercise you can perform while unable to carry on a conversation).

Sources:
Stronger, Faster, Smarter http://www.msnbc.msn.com/id/17662246/site/newsweek/
Exercise Is a State of Mind http://www.msnbc.msn.com/id/17662247/site/newsweek/
On Your Marks... http://www.msnbc.msn.com/id/17662257/site/newsweek/