All In Your Head
Author : by Richard Restak, M.D.    -   Subject : Life

    New research shows that what you thought about the aging brain is all wrong. Especially the bad stuff.

    If you thought your brain was like a sitcom—going slowly downhill with each passing year—prepare to be surprised. New research shows that aging brains are far more vigorous, far more resilient, and far more fertile than previously thought. "Our brains have an innate capacity for change no matter how old we are," says neuropsychologist Marilyn Albert, Ph.D., of the Harvard Medical School, and a star of the five-part PBS series The Secret Life of the Brain, starting in January.

    If you want proof of the aging brain's potency, meet Viktor Korchnoi. Last August, the 70-year-old won the elite Biel International Chess Festival in Switzerland, defeating the Russian champion, Peter Svidler, 25. Korchnoi's victory surprised many chess fans. But it's not all that surprising to students of the brain. A battery of new research shows that language skills, IQ, abstract thinking, and verbal expression all hold steady in the aging brain, except when attacked by diseases such as Parkinson's and Alzheimer's. In fact, where sheer mental agility is concerned, our brain capacity may keep expanding for as long as we live.

    If you're looking for an area where we hold a clear advantage over youngsters, we've got one: the ability to put things in context and reach a good decision with less information—otherwise known as wisdom. Ever notice that the people who occupy positions of responsibility and power tend to be 50-plus? In the judicial system alone, almost 40 percent of the nation's more than 1,200 federal judges are over 65. "Older people may process information and react to that information a bit more slowly, but that slight lag in speed is more than made up for by the knowledge they've accumulated over the years," explains Denise Park, Ph.D., a research scientist at the Center on Aging and Cognition at the University of Michigan in Ann Arbor. "As we age, we get better at mulling over situations, reflecting on them, and drawing upon our life experiences to arrive at decisions."

    The brain is a lot like Michael Jordan (though, unfortunately, without the endorsement deals). Sure, Jordan is no longer the fastest player on the court, and he doesn't soar above the rim like he did in his 20s, but he's still a dominant player for a simple reason: He changed his game to maximize his strengths and minimize his weaknesses. Which is pretty much what the brain does. Only instead of dealing with a loss of hang time, your brain is coping with limited storage space. You've been there and done that a lot longer than any wet-behind-the-ears 20-year-old, which means you've got more stuff to remember. And any new memories (the name of the guy you promised you'd call after the Christmas party, or where you put the receipt for the crystal vase you want to return) have to fight for space with old memories. After 60, as a result of this lifetime overload, long-term memory is less reliable.

    The aging brain is also slower at manipulating information—seeing something, remembering it, and acting on it. This decline can be traced to slower-acting frontal lobes of the brain. Think of the frontal lobes as the grunt-work area: where data is processed, sorted, and retrieved on demand.

    But to compensate for the drop-off in power and speed, the brain does something clever. It finds help. Park discovered this when she compared brain activity patterns in older and younger people. In one telling test, subjects were asked to look at a picture for two seconds. Then the picture was taken away and they were asked to maintain a "mental image" of it. After four seconds, they were shown a small fragment of a picture and asked whether it was part of the original.

    Younger subjects generally scored higher on this test. But Park observed an interesting phenomenon: "When looking at the picture, young adults primarily activate their right visual cortex and right hemisphere. Older adults, in contrast, activate both sides of their brain about equally."

    What's happening, researchers like Park believe, is that the older brain is compensating for its declining processing power. Kind of like using two hands to pick up a heavy object instead of one.

    "The older brain is more resilient than we think," says Randy McIntosh, Ph.D., assistant professor of psychology at the University of Toronto. In a study co-led by McIntosh, young and old performed a memory task equally well, even though the signals sent across nerve synapses in the brain were measurably weaker in older subjects. But the older brains rerouted some of these messages across underutilized areas of the brain, including the hippocampus. The hippocampus is generally reserved for more complicated memory tasks, such as memorizing a lengthy section from Hamlet.

    All of which may explain a separate but related point. Many of us have a feeling as we pass milestone birthdays that our minds are operating differently than they did in our youth. Park's and McIntosh's studies suggest that those feelings are right. On a biological level, the older brain is a different brain.

    The older brain is also capable of rebuilding its weakened structures through a process called neurogenesis (the creation of nerve cells). Why is this so significant? Because neurogenesis—if it can be controlled and directed—might reverse the effects of Parkinson's and other degenerative brain diseases that are the scourge of old age. Dementia affects more than 40 percent of Americans over 80, and at least one person in four over the age of 85 is afflicted with Alzheimer's disease.

    Neurogenesis is a breakthrough concept in our understanding of the aging brain. Three years ago, researchers had no evidence that a mature brain could spawn new neurons. Then in November 1998, Fred Gage, Ph.D., and his team at the Salk Institute in La Jolla, California, along with another team at the Sahlgrenska University Hospital in Sweden, announced the discovery of stem cells—primitive, unspecialized cells that morph into mature cells—within the hippocampus. That in itself was big news, but scientists now know that stem cells aren't restricted to this one brain site. "Stem cells can divide, move around in the brain, end up in specific locations, and then fully differentiate into neurons," says Gage.

    Dr. Jeffrey Macklis, M.D., of Children's Hospital, in Boston, has taken the first steps in activating stem cells in the brain and encouraging them to migrate to damaged areas. He recently grew new neurons in the cerebral cortexes of mice from cells already existing in their brains. If his work can be replicated in humans, treatments might become available for certain degenerative brain diseases. A disease with great potential for this is Parkinson's. Unlike Alzheimer's, which is spread throughout the brain and is tough to target with stem cells, Parkinson's is marked by relatively simple defects.

    Another strategy is to harvest stem cells from other sources and insert them into the brain's damaged areas. The challenge is figuring out how to make them do what's needed: "You can't just put stem cells in the brain and expect them to take over the function of missing or damaged cells," says Gage. "You have to figure out the requirements for turning these cells into neurons."

    Today Gage is experimenting with cells and attempting to "educate" them. That is, to spur them into becoming fully mature, chemically active, electrically responsive neurons. "We train the stem cells in a culture dish and expose them to appropriate chemical stimulants before we transplant them into the brain at a more mature stage," he says. "We think of it as sending them to high school, then college, and then graduate school before we put them back into the brain to do their job. Right now we're trying to figure out the training regimens so that when we put them into a damaged brain area they will turn into the kind of cell that we want."

    Despite the ongoing research, we're not there yet, cautions Macklis. "But I believe over the next decade or so we're going to make substantial progress toward human therapies."

    In the meantime, there's plenty we can do to keep our own brains in good shape. At the top of the list is exercise. Exhibit A: 94-year-old Milton Adamson. Adamson works out every morning—15 minutes of stretching and floor exercises—a regimen he's been following for more than 50 years. And in a recent series of memory tests, Adamson scored as high as people half his age. Researchers like Carl Cotman, Ph.D., a neuroscientist at the University of California at Irvine, attribute Adamson's scores to robust levels of BDNF, a growth-inducing protein that keeps neurons healthy. "Exercise stimulates the production of all kinds of wonderful molecules that keep neurons strong," says Cotman. "I think of them as molecular fertilizer. And exercise actually increases these molecules in the brain."

    The Archives of Internal Medicine recently reported that older women who started a walking program showed lower levels of cognitive decline than sedentary women when tested six to eight years later. Animal studies have found that rats that spend hours on running wheels have higher levels of BDNF than couch-potato rats. Research by Gage shows that exercising mice create twice as many brain cells in the hippocampus region as lounge lizard mice.

    Just about any physical exercise will increase cell activity in the brain, from running to weightlifting to walking. Even more relaxed activities like tai chi can boost brain cells, although in general the greater the increase in heart rate and the greater the intake of oxygen into the body, the better the effect on the brain. Mental exercise is equally important: reading, doing puzzles—challenging your mind. If you work your brain, your brain benefits, says neuroscientist Willian Greenough, Ph.D., of the University of Illinois. You either use it or lose it.

    Researchers like Greenough are now hard at work on the next step in brain research: developing an all-encompassing theory of how the organ works. The emphasis for research has largely shifted from structure to form—scientists now regard the brain not as a shell but as an active, dynamic, supremely plastic structure that changes from moment to moment.

    "I think it remains unknown whether or not there's an upper limit to brain survival," says Gage. "Most people die, not because their brain has aged, but because of deterioration elsewhere in the body. If we can maintain a healthy, functioning brain with continued self-renewal, I believe we can have a fully functioning or at least well-functioning brain for a longer period of time than our current estimates. It is important to remember," he adds, "that we have just begun to understand the functioning of the human brain." In other words, the best is yet to come.

    Richard Restak, M.D., is a neurologist in Washington, D.C., and the author of The Secret Life of the Brain, a companion book to the PBS series.

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