There you are at a business function and you see a colleague across the room. As you walk over, you suddenly realize you can't remember the person's name. Odds are you're not suddenly developing Alzheimer's disease, although many people jump to that conclusion. You're simply experiencing a breakdown of the assembly process of memory -- a breakdown that many of us begin to experience in our 20s and that tends to get worse as we reach our 50s. This age-dependent loss of function appears in many animals, and it begins with the onset of sexual maturity.
We saw earlier in this chapter that as you learn and remember, your brain doesn't change its overall structure or grow whole new batches of nerve cells -- it's the connections between cells that change as you learn. Your synapses are reinforced, and cells make more and stronger connections with each other. But as you begin to age, these synapses begin to falter, which begins to affect how easily you can retrieve memories.
Researchers have several theories about what's behind this deterioration, but most suspect that aging causes major cell loss in a tiny region in the front of the brain that leads to a drop in the production of a neurotransmitter called acetylcholine. Acetylcholine is vital to learning and memory.
In addition, some parts of the brain that are essential to memory are highly vulnerable to aging. One area, called the hippocampus, loses 5 percent of its nerve cells with each passing decade -- for a total loss of 20 percent by the time you reach your 80s. In addition, the brain itself shrinks and becomes less efficient as you age.
Of course, other things can happen to your brain to speed up this decline. You may have inherited some unhealthy genes, you might have been exposed to poisons, or perhaps you smoked or drank too much. All these things speed up memory decline.
So you can see that as you age, some physical changes in the brain can make it more difficult to remember efficiently. The good news is that this doesn't mean that memory loss and dementia are inevitable. While some specific abilities do decline with age, overall memory remains strong for most people throughout their 70s. In fact, research shows that the average 70-year-old performs as well on certain cognitive tests as do many 20-year-olds, and many people in their 60s and 70s score significantly better in verbal intelligence than do younger people.
Studies also have shown that many of the memory problems experienced by older people can be lessened -- or even reversed. Studies of nursing-home populations show that patients were able to make significant improvements in memory when given rewards and challenges. Physical exercise and mental stimulation also can really improve mental function.
Evidence from animal studies suggests that stimulating the brain can stop cells from shrinking and can even increase brain size in some cases. Studies show that rats living in enriched environments with lots of toys and challenges have larger outer brains with larger, healthier brain cells. And animals given lots of mental exercise have more dendrites, which allow their cells to communicate with each other. Research has shown that, in our later years, a stimulating environment encourages the growth of these dendrites, while a dull environment impedes it.
The important point to remember is that as you age, you may not learn or remember as quickly as you did when you were in school -- but you will likely learn and remember nearly as well. In many cases, an older person's brain may be less effective not because of a structural or organic problem but simply as a result of lack of use.
ABOUT THE AUTHORS:
Richard C. Mohs, Ph.D., has been vice chairman of the Department of Psychiatry at the Mount Sinai School of Medicine and associate chief of staff for research at the Bronx Veterans Affairs Medical Center. The author or co-author of more than 300 scientific papers, Dr. Mohs has conducted numerous research studies on aging, Alzheimer's disease, and cognitive function.
Carol Turkington is a freelance writer who specializes in the fields of health and psychology. A former editor and writer for the Duke University Medical Center and the American Psychological Association, she has more than 40 books to her credit, including The Memory and Memory Disorders Sourcebook; The Encyclopedia of Memory and Memory Disorders; and The Brain Encyclopedia.