How the Mind Ages

Mental function with age is largely determined by mental lifestyle, the impact of chronic disease and flexibility of the mind.

By Kristin White, published on November 01, 1993 - last reviewed on October 01, 2009

"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.

BEYOND MEMORY

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."