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The Nuns of Mankato

The brain's plasticity not only helps with recovery but may actually play a role in preventing brain disease. For evidence, just visit the School Sisters of Notre Dame nunnery in remote Mankato, Minnesota. Many are older than ninety, and a surprising number reach one hundred; on average they live much longer than the general public. They also suffer far fewer, and milder, cases of dementia, Alzheimer's, and other brain diseases. David Snowdon, the University of Kentucky professor who has been studying them for years, thinks he knows why.

Spurred on by their belief that "an idle mind is the devil's plaything," the nuns doggedly challenge themselves with vocabulary quizzes, puzzles, and debates about health care. They hold current-events seminars every week, and write often in their journals. Sister Marcella Zachman, featured in Life magazine in 1994, didn't stop teaching at the nunnery until she was ninety-seven. Sister Mary Esther Boor, also pictured in Life, still worked the front desk at ninety-nine. Snowdon, who has examined more than 100 brains donated at death by nuns in Mankato and other School Sisters locations across the nation, maintains that the axons and dendrites that usually shrink with age branch out and make new connections if there is enough intellectual stimulation, providing a bigger backup system if some pathways fail.

Snowdon has found that the nuns who earned college degrees, taught school, and constantly challenged their minds into old age lived longer and resisted Alzheimer's disease better than the nuns who had lower levels of formal education and spent most of their time cleaning rooms and preparing food. Snowdon's conclusion, and that of other scientists who have studied aging and the brain, is that any intellectually challenging activity stimulates dendritic growth, which adds to the neural connections in the brain. The more mentally challenged sisters have more neural connections, which allows them to reroute messages when the brain is damaged by stroke or disease, counteracting the debilitating effects on the brain and thus keeping them healthier and more active for more years. Given that the sisters have led otherwise similar lives in the same environment for decades minimizes the influence of any other factor.

The hypothesis that more academic challenge leads to a more flexible brain in old age is supported by gerontologist Denis Evans, who studied elderly residents in the working-class community of East Boston, Massachusetts. He gave them a series of memory and mental status tests, and repeated the testing three years later. Residents who had fewer years of formal education consistently showed a greater decline in test scores, independent of age, birthplace, occupation, income, or native language.

Regeneration

Hope is now growing that brain damage can be treated by inducing neurons to regenerate; recent discoveries indicate that regeneration might be possible. If so, brains damaged by stroke, Parkinson's disease, and Alzheimer's disease could actually produce new brain cells to fill the roles of the cells that have died. It is true that most neurons can't be regrown when they die; our brains would have a hard time holding on to memories and skills if cells were easy to replace. However, in a few specific regions, such as the hippocampus, the birth and differentiation of neurons continues through old age.

In studies with adult rats, Alan Lewis of Signal Pharmaceuticals found that new, undifferentiated neurons taken from brain areas that are still growing and moved to another part of the brain can learn to perform the local function there. Lewis grafted immature nerve cells from memory areas into smell areas; the cells used cues from the local environment to develop into mature olfactory neurons. Since neurons aren't totally preprogrammed to perform specific functions, neurons moved from one area may be able to take over functions lost to brain damage in another.

Genetic manipulation may also help. Evan Snyder at Harvard Medical School removed newly formed brain cells from newborn mice. He injected them with a gene that would cause them to divide and then inserted them into different areas of brains of adult mice in which stroke had been induced. The implanted neurons migrated to the damaged areas, divided, and took on local specialized functions. One theory is that the cells responded to chemical signals released by dying neurons or by ordinary brain cells that no other cells were responding to. Because actively dividing cells have not yet specialized their function, if they are directed to the right location they may be able to fill in for neurons lost to stroke, disease, or accidents.

Implanting dividing cells that could renew brain function could be a key to fighting Parkinson's, the disease that has ravaged boxer Muhammad Ali and that affects 500,000 to 1 million Americans a year, most over age fifty-five. Parkinson's results from cell death in the substantia nigra, which produces dopamine and sends it to a second brain structure called the striatum, which coordinates movement. No dopamine means no muscular coordination.

One way of restoring the dopamine supply would be to replace the faltering substantia nigra neurons with ones that work. The question is where to get the immature neurons. Until recently the only source was brain tissue from aborted human fetuses. The first fetal transplants a decade ago were promising but prompted isolated instances of public outcry, reported in the media with persistent Frankenstein clich?s. President Bush promised to ban the technique, just as President Clinton would later vow to do for human cloning. However, research continued in Europe and in privately funded ventures in America. In 1993 the U.S. presidential disapproval was lifted. No conclusive clinical trial of the process has yet been completed. Only 200 transplants have been carried out at the universities of Lund, in Sweden, and Colorado, at Denver, so the real value of the treatment is only just being discerned.

Excerpted from A User's Guide to the Brain by John J. Ratey, M.D. Copyright © 2002 by John J. Ratey, M.D.. Excerpted by permission of Vintage, a division of Random House, Inc. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.

Tags: Neuropsychology

About the Author

John J. Ratey, M.D., is an associate professor of psychiatry at Harvard Medical School. He has lectured extensively and published many articles on the topic of treating adults with ADD. Dr. Ratey is the author of A User's Guide to the Brain and the co-author of Driven to Distraction. He lives in Cambridge, Massachusetts, where he has a private practice.