Healing Through Exercise: Scientifically Proven Ways to Prevent and Overcome Illness and Lengthen Your Life (16 page)

The psychologist Arthur Kramer of the University of Illinois in Urbana-Champaign was able to demonstrate the presence of this atrophy when he looked at the brains of 55 healthy elderly persons, using magnetic resonance imaging (MRI). But Kramer also had good news, at least for those people who had always been active. They were not only in good shape, but on average their brain atrophy was not as pronounced as that in sedentary people. Furthermore, they had specifically retained structures in the lateral and frontal areas of the brain, which are most important for complex cognitive functions.

After this finding, Kramer and his colleagues wanted to check whether moderate exercise might even reverse the usual course of brain atrophy. Healthy but sedentary volunteers aged 60 to 79 participated in an aerobic training program for six months (consisting of one-hour sessions, three days per week). To provide a comparison, other volunteers of the same age also met three days per week in the gym. But instead of true exercising, they just did some stretching.

The astonishing result has been published in the
Journal of Gerontology
.
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Parts of the brain actually increased in size for aerobic exercisers! The enlarged areas were primarily located in prefrontal and temporal cortices, the same regions often reported as showing substantial age-related deterioration. Declines in these areas are linked to a broad array of clinical symptoms including Alzheimer’s disease. In the group that just did some stretching, such enlargements could not be found.

If this novel and intriguing finding is further confirmed, it will have profound repercussions for the prevention of neurodegenerative diseases. The results suggest that brain volume loss is not an inevitable effect of advancing age and that relatively minor interventions can halt or slow down this loss. Moderate exercise not only helps stave off the onset of cognitive decline, but it might have the potential to halt and even
reverse
the loss of brain structures in old age! These implications did not escape the attention of the researchers. They conclude that their results “directly bear on issues of public policy and clinical recommendations in that they suggest a rather simple and inexpensive mechanism to ward off the effects of senescence on human brain tissue.”
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Responsible doctors are prudent enough not to raise hopes that Alzheimer’s patients will have effective drugs available to them in the foreseeable future. At the same time, surveys show that more than 40 percent of adults who are 50 or older are afraid of losing control of their minds someday because of Alzheimer’s disease. Science has rarely provided us with better arguments to start moving.

TRAINING IS THE BETTER PILL

As soon as we start sweating, we help our brains. As we saw, growth factors and neurotransmitters start circulating in higher numbers through the brain. Next, the number and length of connections between the nerve cells increase. One could say that the whole brain becomes jazzed up from inside, making it more malleable and more plastic than before. Yet there is an even more astonishing rejuvenator, which we will discuss in the following chapter; exercise appears to promote the growth of new nerve cells in old brains.

A Fountain of Youth in the Brain

E
VERY DAY, THE NEUROSCIENTIST JEFFREY MACKLIS OFFERED HIS MICE A new treat to sniff. One morning, he would blow the smell of chocolate into their cage; the next, he would let them breathe clouds of rosewater.

This way, Macklis introduced the mice to a previously unknown world. The animals were raised in scent-proof habitats and had not experienced a single one of the dozen odors they had been smelling in the course of his experiment. How would their brains respond to novel stimuli?

Macklis and his colleagues at the Center for Nervous System Repair at Massachusetts General Hospital and Harvard Medical School in Boston were the first researchers to see what happens in the part of the brain where odors are processed. They achieved this feat by following the fate of new nerve cells that migrate to the olfactory bulb, the brain region enabling us to sense smells. There, new nerve cells appear to originate all the time. But only when animals smell a previously unknown scent do these nascent nerve cells mature into active neurons that integrate themselves into the brain’s circuits two to three weeks later. The nerve cells develop long axons and make numerous connections—synapses—to other neurons. In contrast to these new arrivals, the older neurons that form the existing network within the olfactory bulb barely get excited by a new odor. “The new neurons are not replacing the old ones,” says Macklis. “They have a unique function: learn new smells.”
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New nerve cells for new memories: Elkhonon Goldberg, a clinical psychologist at New York University, believes in this formula, too. Time and again, in his office, two blocks south of Central Park, elderly individuals show up who often misplace their keys, leave the stove burning, or forget what is on the pages of the books they have just read.

To combat their forgetfulness, Goldberg prescribes a program intended to improve several cognitive functions, such as vocabulary retention, mental agility, and spatial perception. To create this program, the psychologist analyzed 200 tests used for the treatment of stroke patients and combined the elements of nearly 60 of them. Two days per week, he requires patients to solve problems presented on a computer screen. A typical task during one such hour-long session is to determine the pattern underlying an arrangement of colored triangles, squares, and circles.

Each individual program usually runs for three months, and at the end Goldberg assesses whether the sessions have improved his patients’ memories in everyday life. After the first 100 patients who tried this course, says Goldberg, he was “pleasantly impressed.” In around 60 percent of the cases, incremental memory loss had been stopped; in 30 percent, the patients’ power to recall things had actually improved.

“Our successes are probably due to the growth of fresh nerve cells in the brain,” says Goldberg. “Cognitive activities can trigger the birth of new neurons.”
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NEUROGENESIS: NEW NERVE CELLS IN THE BRAIN

A fountain of youth in the brain? New mental power thanks to new nerve cells? Until recently, Macklis and Goldberg would have been dismissed as dreamers because they call into question a seemingly irrefutable dogma: our nerve cells lose their power to divide shortly after we are born. If so, the human brain could at best keep its established level of mental capacity, which in most cases would shrink with age.

But these days, neurologists, biochemists, and physicians see more and more data indicating otherwise: new nerve cells do grow in certain parts of the adult brain. With awe and surprise, researchers realize this process—called neurogenesis—appears to be essential for the normal functioning of the brain.

“We are beginning to see the brain from a completely different perspective,” says Gerd Kempermann, a leading expert on neurogenesis now at the Center for Regenerative Therapies in Dresden.
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“There is a positive tendency: The development of the brains goes on during the whole life.”

It is especially encouraging that new nerve cells sprouting in old brains turn out to be particularly malleable and flexible. For that reason, they seem to contribute to the astonishing reserve capacities that allow the brain to master difficult and unexpected challenges. Kempermann says: “The neurogenesis is probably a fundamental precondition for staying mentally alert up to high age.”

The emerging picture of neurogenesis implies that genetics alone do not determine whether people retain mental acuity throughout their lives. Rather, lifestyle—the way we treat the brain—has tremendous repercussions on its ability to renew itself. And, among these ways, it’s physical exercise that appears most important because it promotes the production of fresh nerve cells.

The effect of neurogenesis on exercise is apparently due to an ancient mechanism shaped by evolution: the more an animal moves around in its environment, the greater the likelihood that it will encounter novel situations. Thus, the brain of an active creature produces especially high numbers of nerve cells that can be used to process these new stimuli. The new cells mature into fully functioning neurons when they are challenged with new tasks. In the absence of such challenges, it is thought, a big portion of the new nerve cells die before long. And in the absence of physical activity, the production of new nerve cells largely ceases.

It’s not easy to prove that neurogenesis takes place in the adult brains of humans. Nearly all of the relevant data stem from animal studies because, for obvious reasons, scientists cannot perform crucial experiments on humans (such as tracing radioactive bits of DNA in neural networks) to see if nerve cells are new. However, a growing body of indirect evidence leaves no doubt neurogenesis takes place in the human brain. American scientists have published an especially convincing study. They encouraged 11 healthy women and men to train for three months in the gym at Columbia University in New York and thereafter analyzed their brains by magnetic resonance imaging (MRI). In the course of the workouts, a particular area within the hippocampus became increasingly supplied with blood. Parallel studies on mice by the same scientists revealed what this means: new capillaries as well as new nerve cells grow there.
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Fred Gage, of the Salk Institute in La Jolla, California, was among the researchers who carried out this study. He and his co-workers Gerd Kempermann and Henriette van Praag first showed that physical exercise can literally act as a fertilizer for the brain. They discovered this by keeping mice in cages with running wheels, so the animals could run as much as they liked. The mobilized mice produced an above-average number of new nerve cells, compared to mice kept without the wheels.
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The effect was actually so big that, ever since Gage’s findings were published, researchers studying neurogenesis also keep their mice in environments allowing them to move. Only under these circumstances do the mice produce fresh neurons in numbers large enough to be studied.

However, does this supply of fresh nerve cells actually make the mice smarter? This is what Henriette van Praag, then a senior researcher in the Gage lab, was able to prove.
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Her experiments actually started when a small biotech company in La Jolla went out of business. The firm had lab mice left over and asked van Praag if she might need some. She happily accepted the offer because these mice were exactly the kind she had been looking for. The animals were 19 months old (equaling a human age of 60), and they had been kept all their lives in small and narrow cages. Thus they were ideal for studying the impact of exercise on old, dulled brains.

Van Praag put half of these mice into cages equipped with running wheels, where the rodents usually ran more than three miles per day. The other half were still kept in cages without the benefit of exercise. After 35 days, van Praag tested the memories of all the mice by putting them into a special water maze. It consisted of a small pool with a shallow platform in the middle, just under the surface. Because mice dislike swimming, they stay on the platform whenever possible, and when repeatedly dropped into the water, will eventually memorize the platform’s location and swim to it.

It turned out that the performance of mice in this environment correlated to the amount of exercise they had been granted. “The aged and sedentary mice just swam around and gave up. Many of them floated and waited for me to take them out of the pool,” Praag recalls. Whereas it took these sedentary animals an average of 30 seconds to find the platform, the physically fit mice needed only 15 seconds to get there.

But was this enhanced learning really due to the production of new nerve cells? To find an answer, the mice were sacrificed and their brains studied 10 days after the test to determine the number of new nerve cells in their brains. Indeed, the mice that had been allowed to run in their cages, and had performed well in the test, had significantly more new neurons in the hippocampus. The brains of these aged runners, who had formerly been kept for so long in narrow cages, had been rejuvenated by exercise.
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Henriette van Praag is convinced that elderly people can benefit greatly from physical exercise. She believes it is worthwhile to “buy your aging relatives a treadmill.” Fred Gage has a similar take on this himself and exercises regularly (he plays squash, runs, and does light weightlifting). The slim and energetic neuroscientist has changed how people see the brain. When I visited him in his lab, he told me: “Your brain is not a computer but a plastic organ—and the way it changes can be controlled by you.”

The discovery of neurogenesis not only changes our perception of the healthy brain but also alters our understanding of why and how brains develop certain illnesses. Alzheimer’s disease, which leads to the loss of many mental functions, and the movement disorder Parkinson’s disease, were until recently usually ascribed to the loss and death of nerve tissue. Now, physicians are starting to rethink matters and view things from a different perspective. Are these untreatable diseases triggered because the production of new nerve cells is stalling?

Also, for learning disorders, depression, alcoholism, nicotine addiction, and schizophrenia, researchers increasingly discuss whether a lack of neurogenesis might play a role—and what sort of activity, including physical exercise, appears to help against precisely these diseases. The scientific exploration of neurogenesis “has evolved into one of the most interesting and most promising projects of modern neuroscience and in particular of molecular psychiatry,” concludes Amelia Eisch of the University of Texas’s Southwestern Medical Center in Dallas.
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