By Kristin White, published on November 1, 1993 - last reviewed on June 19, 2012
Mental function with age is largely determined bythree factors--mental lifestyle, the impact of chronic disease, and flexibility of the mind.
Over a lifetime, everybody changes inwardly as well as outwardly. The mind too, changes, although the petty pace at which we creep from day to day often keeps most of us unaware of how, even during adulthood, mental functions continue to evolve as we grow older.
The huge population bulge known as the "Baby Boom," reaching the major mileposts of maturity (marriage, parenthood) roughly 10 years behind schedule, has forced a culture-wide reevaluation in thinking about what aging feels like. Research now suggests it's time to revolutionize our thinking about what aging actually is, particularly in the most revered precinct, the human mind.
Aging, it is now clear, is part of an ongoing maturation process that all our organs go through. "In a sense, aging is keyed to the level of vigor of the body and the continuous interaction between levels of body activity and levels of mental activity," reports Arnold B. Scheibel, M.D., whose very academic title reflects how once far-flung domains now converge on the mind and the brain. Scheibel is professor of anatomy, cell biology, psychiatry, and behavioral sciences at the University of California at Los Angeles, and director of the university's Brain Research Institute.
Conventional wisdom has it that, as the vigor of the body declines, the power of the mind diminishes as well. Indeed, older people seem to slow down mentally; they often become garrulous, forgetful, crotchety, and some develop outright dementia.
Experimental evidence has backed up popular assumptions that the aging mind undergoes decay analogous to that of the aging body. Younger monkeys, chimps, and lower animals consistently outperform their older colleagues on memory tests. In humans, psychologists concluded, memory and other mental functions deteriorate over time because of inevitable organic changes in the brain as neurons die off. Mental decline after young adulthood appeared inevitable.
The truth, however, is not quite so simple. Some functions peak early in life, others don't get up to speed until adolescence or early adulthood. There are mental capabilities, like judgment and wisdom, that continue to improve as you grow older even as others, like short-term memory and the ability to do tasks within a set time limit, may start to decline in your 40s.
Although many mental functions actually begin to fall off or reach their peak at about age 24 to 28, adults do continue to learn, and their mental programming refines itself. What's more, research over the past decades shows that the mind constantly adjusts its way of doing things and compensates nicely for many losses in efficiency. The brain, too, is almost infinitely plastic, containing many more neurons (with more potential connections between them) than we can use. If one neuron fails, those nearby can take on its load.
Equipped with imaging techniques that capture the brain in action, Stanley Rapoport, Ph.D., at the National Institutes of Health, measured the flow of blood in the brains of old and young people as they went through the task of matching photos of faces. Since blood flow reflects neuronal activity, Rapoport could compare which networks of neurons were being used by different subjects.
"Even when the reaction times of older and younger subjects were the same, the neural networks they used were significantly different. The older subjects were using different internal strategies to accomplish the same result in the same time," Rapoport says. Either the task required greater effort on the part of the older subjects or the work of neurons originally involved in tasks of that type had been taken over by other neurons, creating different networks.
At the Georgia Institute of Technology, psychologist Timothy Salthouse, Ph.D., compared a group of very fast and accurate typists of college age with another group in their 60s. Since reaction time is faster in younger people and most people's fingers grow less nimble with age, younger typists might be expected to tap right along while the older ones fumble. But both typed 60 words a minute.
The older typists, it turned out, achieved their speed with cunning little strategies that made them far more efficient than their younger counterparts: They made fewer finger movements, saving a fraction of a second here and there. They also read ahead in the text. The neural networks involved in typing appear to have been reshaped to compensate for losses in motor skills or other age changes.
There's solid evidence that deterioration in mental functions can actually be reversed. It is certainly true of laboratory animals, probably of humans as well. Neuropsychologist Marion Diamond, Ph.D., and others at the University of California at Berkeley have shown that mental activity makes neurons sprout new dendrites with which to establish connections with other neurons. The dendrites shrink when the mind is idle.
"When a rat is kept in isolation without playmates or objects to interact with, the animal's brain shrinks, but if we put that rat with 11 other rats in a large cage and give them an assortment of wheels, ladders, and other toys, we can show--after four days--significant differences in its brain," says Diamond, professor of integrative biology. Proliferating dendrites first appear in the visual association areas. After a month in the enriched environment, the whole cerebral cortex has expanded, as has its blood supply.
Even in the enriched environment, rats get bored unless the toys are varied. "Animals are just like we are. They need stimulation," says Diamond.
A recent study from the University of California at Los Angeles adds a certain amount of emphasis to that point. Researchers looking at the brains of adults--specifically Wernicke's area, the part of the brain devoted to word understanding--found that the number of dendrites correlates with the amount of education. College graduates have more dendrites than high school graduates, who, in turn, have more than people who topped out at grade school. The implication: education gives people practice in saying and hearing words, a special kind of mental activity that enriches Wernicke's area with dendrites.
When put through maze tests, the alumni of Diamond's enriched environment outscore rats that have spent their lives in ordinary cages or alone.
"You know yourself that if you've been sitting around for a couple of months it takes a while to get back up to speed, physically or mentally. If the dendrites have come down, you've got work to bring them back again. But the brain's wonderful plasticity remains throughout life," says Diamond.
EDUCATION vs. AGING
One of the most profoundly important mental functions is memory-notorious for its failure with age. So important is memory that the Charles A. Dana Foundation recently spent $8.4 million to set up a consortium of leading medical centers to measure memory loss and aging through brain-imaging technology, neurochemical experiments, and cognitive and psychological tests. One thing, however, is already fairly clear--many aspects of memory are not a function of age at all but of education.
Memory exists in more than one form. What we call knowledge--facts--is what psychologists such as Harry P. Bahrick, Ph.D., of Ohio Wesleyan University calls semantic memory. Events, conversations, and occurrences in time and space, on the other hand, make up episodic or event memory, which is triggered by cues from the context. If you were around in 1963 you don't need to be reminded of the circumstances surrounding the moment you heard that JFK had been assassinated. That event is etched into your episodic memory.
When you forget a less vivid item, like buying a roll of paper towels at the supermarket, you may blame it on your aging memory. It's true that episodic memory begins to decline when most people are in their 50s, but it's never perfect at any age.
"Every memory begins as an event," says Bahrick. "Through repetition, certain events leave behind a residue of knowledge, or semantic memory. On a specific day in the past, somebody taught you that two and two are four, but you've been over that information so often you don't remember where you learned it. What started as an episodic memory has become a permanent part of your knowledge base."
You remember the content, not the context. Our language knowledge, our knowledge of the world and of people, is largely that permanent or semipermanent residue.
Probing the longevity of knowledge, Bahrick tested 1,000 high school graduates to see how well they recalled their algebra. Some had completed the course as recently as a month before, others as long as 50 years earlier. He also determined how long each person had studied algebra, the grade received, and how much the skill was used over the course of adulthood.
Surprisingly, a person's grasp of algebra at the time of testing did not depend on how long ago he'd taken the course--the determining factor was the duration of instruction. Those who had spent only a few months learning algebra forgot most of it within two or three years.
In another study, Bahrick discovered that people who had taken several courses in Spanish, spread out over a couple of years, could recall, decades later, 60 percent or more of the vocabulary they learned. Those who took just one course retained only a trace after three years.
"This long-term residue of knowledge remains stable over the decades, independent of the age of the person and the age of the memory. No serious deficit appears until people get to their 50s and 60s, probably due to the degenerative processes of aging rather than a cognitive loss."
If you're 30 and want to learn to play the piano, you'd be better off taking one lesson a week for a year than two weekly lessons for six months. And, instead of practicing for seven hours on Sunday afternoons, practice one hour every day.
What a person already knows helps him to learn new material. New information can be fixed securely in the memory if scaffolding is in place for it to fit in.
Perhaps even more important than the ability to remember is the ability to monitor and manage memory--a mental function known as metamemory ("beyond memory") or "metacognition."
Children as young as three already have a sense of how well they can remember things, but metamemory keeps on developing throughout childhood. With their undiscriminating "Cookie-Monster" minds, toddlers gobble up all the information they encounter. They just can't organize or monitor this wealth.
If your three-year-old nephew remembers your wristwatch or your car better than your face, it's because the details of your last visit are jammed higgledly-piggeldy into a disorganized memory. It's easier for the child to call up some items, impossible to retrieve others, because his metamemory isn't sufficiently developed to organize the data in his mind.
"You could say metamemory is a byproduct of going to school," says psychologist Robert Kail, Ph.D., of Purdue University, who studies children from birth to 20 years, the time of life when mental development is most rapid. "The question-and-answer process, especially exam-taking, helps children learn--and also teaches them how their memory works This may be one reason why, according to a broad range of studies in people over 60, the better--educated a person is, the more likely they are to perform better in life and on psychological tests.
A group of adult novice chess players were compared with a group of child experts at the game. In tests of their ability to remember a random series of numbers, the adults, as expected, outscored the children. But when asked to remember the patterns of chess pieces arranged on a board, the children won. "Because they'd played a lot of chess, their knowledge of chess was better organized than that of the adults, and their existing knowledge of chess served as a framework for new memory," explains Kail.
Things may be different, however, with different types of cognition. At the University of Oregon, Michael I. Posner, Ph.D., deploys brain-imaging techniques to map the neural networks involved in the task of paying attention. He has found that the neurotransmitter norepinephrine is involved in the alerting function that allows us to focus attention on one object, and in the inhibitory mechanism that helps us screen out irrelevant stimuli. Age-related failures in this system, he thinks, might account for the way older people are easily distracted and tend to ramble on in conversation. "Attentional systems, like any mental activity that involves speed and Puts stress on the system, show a big decline over age 70," he reports.
Georgia Tech's Timothy Salthouse detects age-related disparities in certain kinds of reasoning functions, such as spatial ability. Subjects are shown a pattern and then asked to turn it mentally and view it from another angle. "If we give the same fairly simple cognitive tests to 30 or 40 people in their 20s and to others in their 40s, we can spot some clear differences," Salthouse says.
Cross-sectional studies of this kind dominate the literature; recruiting and studying at one time lots of people of different ages is simpler and cheaper than following individuals throughout life and testing them periodically. Cross-sectional studies assume that today's 60-year-old is what today's 40-year-old will be like 20 years from now. But even Salthouse, who conducts such studies, warns such an assumption can be wrong.
"Test-score differences between age groups aren't necessarily caused by inevitable, irreversible biological changes," muses Salthouse. The world is changing under our feet, it seems. "There's more cultural stimulation nowadays, which might give an advantage to people who grew up with television, Head Start programs, and other influences that weren't around earlier."
Still, he thinks that the available evidence supports the inference that any differences between college students and older people more or less reflect the changes that go on in individuals, and that downward changes really do begin as early as the 20s.
Using different methods, psychologist Warner Schaie, Ph.D., has detected no differences in various kinds of cognition until age 60. "After that, we find great individual differences over the next 20 years, with some people going downhill dramatically and others doing as well as ever."
Schaie logs nearly 40 years of longitudinal research that began with his doctoral dissertation. A few of his first subjects continue to return every seven years for tests that monitor their verbal, numeric, and spatial reasoning, perceptual speed, various kinds of memory, and other mental abilities. His test population comes from a large Seattle HMO.
The 1991-1992 wave of testing, yielding data on over 1,000 people, included 75 of the original subjects returning for their sixth round of tests. All told, there's data on about 5,000 people. The study is virtually unique in its size and duration, and even researchers who disagree with some of Schaie's conclusions are quick to concede that their data aren't nearly as solid.
The research indicates strongly that the period between ages 50 and 60 is diagnostic-people in their 50s who show signs of fading won't do well mentally in later years, when it's virtually impossible to structure a new set of mental habits. After 50, mental function is largely determined by three factors--the mental lifestyle, the impact of chronic disease, and the flexibility of the mind.
THE BIG THREE
In humans, as in laboratory animals, a busy mental lifestyle keeps the mind fit, says Schaie, now director of the gerontology center in the College of Human Development at Penn State. "People intensely involved in life retain their intellectual abilities better than mental couch potatoes." The conclusion may sound cliched, but it's drawn from the test scores of serious bridge players and crossword-puzzle fanatics. Their cognition decreases less with age than that of people whose most challenging pastime is bingo.
"A person who stops solving problems arrives at a point where he can't solve problems," Schaie declares.
Generally, people who develop chronic diseases after age 50 function less well mentally than they did before they became ill. In his studies, Schaie detected a decline in mental function among individuals who underwent lengthy hospitalizations for cancer, heart disease, or other chronic illness. The loss, however, was modest, suggesting it was not the direct effect of disease. He postulated it might be due to the passivity and mental indolence encouraged by hospital routine.
Schaie's wife and colleague, Sherry Willis, Ph.D., tested this idea by giving puzzlelike assignments in problem-solving and reasoning to a group of long-term hospital patients over age 65, then coached them in mental strategies and short cuts. Their cognition improved. Seven years later, they retain their renewed mental vigor.
Cognitive style, the third factor in maintaining mental function, is what Schaie calls "the ability to adapt and roll with life's punches." He measures mental rigidity and flexibility with questions ("Do you insist on having a place for everything and everything in its place?") and tests requiring people to perform familiar tasks in an offbeat way. For example, he will ask people to copy a paragraph substituting uppercase letters for lowercase ones.
"These tests seem silly, but flexible-minded people manage to complete them," says Schaie. "They laugh. The rigid person responds with tension and dithering instead, forcing himself through the exercise and performing poorly." Those who score highly on tests of cognition at an advanced age are those who tested high in mental flexibility at middle age.
GETTING OLDER, GETTING BETTER
The great individual variability in tests of mental function that shows up as people age suggests something crucial: major deterioration is not preordained by nature. Substantial decline is not necessarily built into the brain. What commonly occurs must not be interpreted as inevitable.
Every psychologist knows that as we live our unique histories we develop in increasingly divergent ways. No doubt, we're building our own customized assortment of neural networks.
Between birth and maturity, the brain triples its weight although vast numbers of brain cells die. During the first year of life this cell decline is so dramatic that any later cell losses look trivial by comparison. But, under the influence of stimulation and education, the surviving brain cells go forth and multiply their connections. They develop increasingly elaborate networks of dendrites with which to communicate with each other. Hard data from a number of labs suggest that in a healthy brain, whenever one cell is lost, its neighbors respond by adding dendrites, assuming the work of the lost cell.
As the number of dendrites grows, messages move across synapses along increasingly elaborate and interconnected pathways. Repeated mental activity forges the most direct routes, driving the brain to become both more efficient and more versatile overall.
With its ability to adapt as new information comes in, the mind has a built-in capacity for self-improvement throughout life. From the beginning, the systems we use are the ones that are favored, and those that seem functionally superfluous are discarded. Once mental abilities are fully developed, the mind functions with increasing strategic efficiency, like computer programs that debug themselves.
Skills improve as new strategies and short cuts are learned; the grade school child's laborious pencil-and-paper or finger-counting process of adding 26 and 12 becomes a computation most adults can do in their heads.
"If you ask really little kids to add two and two, they'll hold out two fingers, then two more, and count them," observes Purdue's Robert Kail. "Counting is accurate but inefficient. Slightly older children don't use their fingers, but they're counting imaginary ones. Seven- or eight-year-olds retrieve the sum from memory. They've begun to learn it's more efficient to have some basic information ready all the time."
A 12-year-old, asked to multiply 5 times 8, might misremember the product as 42. But then he'd think about it. If he felt unsure, he'd try another way, perhaps adding five 8s together. If he didn't get an answer he felt confident about, he'd try a third method, test his confidence in the answer, and so on. This "strategy-choice model" is the foundation of flowcharts, computer programs, common sense--and it may improve with time.
Once the mind attains its adult level, it goes through these steps automatically. When you're posed a problem requiring an answer, you first check your memory. if you find something that looks like what you want, you check it, test your confidence, and, if you're not sure, go to a backup strategy and test that result.
Kail likes analogies between mind and computer. "The comparison suggests that changes occur in several ways, and that a person's catalog of programs grows with experience. Instead of looking at mental development as simple growth, or a series of leaps, we see it more as debugging."
Each time we address a problem that resembles one we've done before--which we often do in our jobs--we ask whether the current strategy can be improved. We're constantly evaluating different approaches, discarding the less efficient. This is why experience is the best teacher and why practice makes perfect.
THUNK BY CHUNK
Specialized knowledge is a mental resource that only improves with time. Crystallized intelligence about one's occupation apparently does not decline at all until at least age 75, and if there is no disease or dementia, may remain even longer.
Special knowledge is often organized by a process called "chunking." If procedure A and procedure B are always done together, for example, the mind may merge them into a single command. When you apply yourself to a specific interest--say, cooking--you build increasingly elaborate knowledge structures that let you do more and do it better. This ability, which is tied to experience, is the essence of expertise.
When an accomplished baker thinks "angel food cake," for example, essential ideas that beginners often look up in a cookbook spring to the experienced mind in a cluster: egg whites at room temperature, no all-purpose flour, fresh cream of tartar. The information is in a "chunk" that's recalled all in one piece.
Vocabulary is one such specialized form of accrued knowledge. Research clearly shows that vocabulary improves with time. Retired professionals, especially teachers and journalists, consistently score higher on tests of vocabulary and general information than college students, who are supposed to be in their mental prime.
Whatever the cause, it's a truism that many people become dissatisfied with their mental performance as they get older. Someday they may be able to correct any deficiences by taking a pill. "We think many of the deficits that come with age can be modified," says Thomas Crook, M.D., a psychiatrist who is president of Memory Assessment Clinics Inc., a private company based in Bethesda, Md.
His enthusiam is bolstered by the finding that medical patients given a class of drugs to treat hypertension--so-called ACE inhibitors, such as Captopril--spontaneously and inexplicably reported improvements in intellectual abilities. Ever since then, pharmaceutical companies have been trying to concoct drugs to repair deficits in cognition, particularly memory.
Crook's company performs clinical trials of candidate drugs and tests cognition in people of all ages. One test measures ability to recognize individual faces among hundreds flashed one at a time on a screen. A face may appear once, followed by several others, and then appear again.
"In some individuals, test performance does not begin to deteriorate until the late 70s," says Crook. "People of all ages make mistakes, even when a photo is presented twice in succession. The problem lies in attending to the task, not in the memory."
Perhaps one day there will be a tablet for regaining full powers of memory, or an injection of norepinephrine for maintaining the ability to pay attention. In the meantime, we have only to rely on the natural self-improvement systems of the mind and the storage capacity of the brain.
We can to some degree outwit the effect of time on the mind by adapting our mental procedures around whatever declines occur. Most of us, sooner or later, will lose in efficiency. We will have trouble juggling several different tasks at the same time. We can do as well as ever on any single one of them by planning work on one thing at a time, with fewer interruptions. And we can perform tasks as well as when younger if we take off the pressure to do them in a limited amount of time.
Best of all, perhaps, we have a great new rationale for slogging away at crossword puzzles.
PHOTO: Microscopic enlargements and cross-sections of brain tissue depicting neurons (DAVID PHILLIPS/PHOTO RESEARCHERS)
PHOTO: axons (BIOPHOTO/PHOTO RESEARCHERS)
PHOTO: capillaries. (SPL/PHOTO RESEARCHERS)
HOW TO AGE-PROOF YOUR MIND
Keep your job. Don't retire. Ever.
Stay physically healthy.
Become an expert in something-anything.
Take up the piano. Take a course in something.
Learn to roll with the punches.
Do crossword puzzles.
Go out with friends or find new playmates.
Learn French in four years, not four weeks.
Turn off the TV.
Stock your life with rich experiences of all kinds.
Play with toys. Lots of them. Different ones.
Skip bingo. Play bridge instead.
BRAIN TRENDS: THE MIND OVER TIME
In the new picture of mental aging, it's not all a matter of "use it or lose it." The brain's placticity remains throughout life.
By high school, people normally develop a strategy framework for problem-solving: 1) check memory to see if answer is stored as fact; 2) test confidence; 3) if answer not found or not satisfactory, go to backup strategy; keep repeating steps 2 and 3 until answer is found. After age 60, vast individual differences are observed over next 20 years; some people go downhill dramatically. By age 80 everybody shows some loss. Persons with active mental life fare better.
By age 50 perception slows noticeably, often because sensory faculties are deteriorating physically or brain connections slow down. Slowing of response after 50 may not be pronounced. Older people score lower only on timed tests, may perform better at tasks that are not timed, Great individual variability in deterioration of sensory perceptual faculties accounts for vast differences in performance.
LEARNING NEW TASKS
Rats that have lived in enriched environment run mazes better than those that have not. People who abandon mental activity when older experience slowing and deterioration of many functions--many reversible when person resumes mental activity.
This encompasses specialized accumulated knowledge. It does not appear to decline at all until after 75, and may remain intact even longer if there is no disease or dementia.
Neurons in parietal lobe orient attention and shift it from one location to another. Network develops between 3-6 months after birth. Attention is controlled by stimulus.
Norepinephrine (arising in locus ceruleus) plays role in alerting posterior areas and activates visual cortex.
Noticing, localized in more anterior parts, develops toward end of first year.
Maintaining alertness takes place in frontal lobes, is responsible for sustained vigilance and detecting meaning in language and other modalities.
Inhibitory controls develop over auditory and visual processing, to suppress irrelevant input.
By college age, attention is fully developed. Over 70, attention declines, possibly because suppression mechanism deteriorates; person is easily distracted, garrulous.
Judgment of own ability to monitor and control own mental processes. Improves with age. After 40, adults may need to make conscious effort to learn, remember, and manage new information as store of memories increases. In elderly, metamemory remains most effective in individuals with active intellects and stimulating lives.
Refers to general ability to adapt and roll with life's punches. Rigid people show declines in mental functioning earlier in life than flexible people. Flexibility in midlife is good indicator of reduced risk of mental decline.
WORKING MEMORY (Random Access)
This is memory to which you refer. It increases through childhood, peaks in 20s. Connections between neurons proliferate with learning, strengthen with use. By acquiring expertise, it becomes easier to acquire knowledge and recall it because there are more neural connections through which to access it. At any age, people easily forget what to buy without a list.
Higher incidence of depression in older people. At any age, depressed mood diminishes mental functioning.
Clearly slows down with age. May take longer to process information in order to retain it.
Personality is crystallized early--cranky old people were usually obnoxious when young--and shows great stability throughout life. Traits that set individuals apart are set by age 30, but people remain able to change if motivated to do so. Some repressed people who had early misfortune may uncover hidden talents. The very old who remain healthy can integrate experiences and enrich personality. Existing traits may be emphasized with age; people become more introspective and sexual stereotypes diminish. Older people may become impatient with trouble doing what once came easily. Only Alzheimer's or other global disease can make personality unrecognizable.
MEMORY: NAMES AND FACES
Fairly rapid onset of deterioration in middle age. Often perceived as worse than truly is. Older people blame forgetting on age, but people generally are not good at any age unless they process the information by associating name/occupation or name/facial features. Very long-term memory of classmates names and faces fades after 3-5 years in absence of further contact. Poor memory at any age may be due to depression or a wish not to remember.
This major memory system, associated with the frontal lobe, registers and stores experience of events in time and space and allows you to retrieve the information; it underlies mental time travel. Requires time and space cues at any age. Memory of new events is retained when there is a rich bed of information to which it can be anchored.
RETRIEVAL OF INFORMATION
Takes longer and involves more errors after 50. As individual ages, more items accumulate in storage, and there are more competing choices as you try to match the specifications of what you want with the characteristics of each item in storage. This is sign your memory is rich and well-stocked.
ILLUSTRATION: (SCOTT MACNEILL)