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Physical exercise may be essential for keeping the brain young as we age, especially for mental tasks that require attention, problem-solving, and making decisions.

About the time we enter our forties, most of us notice our bodies are slowing down. Running, climbing, and reaching may become more difficult. Our sexual stamina may be diminished. We gain weight more easily and lose it with more difficulty, and chronic diseases may begin to set it.

The usual prescription for avoiding these early signs of aging is to exercise. It turns out, recent studies have found, that physical exercise also helps preserve our mental abilities.

"Middle Aging" of the Brain

As we go into the fifth decade of our lives, the way our brains work begins to change. It's as if the "toggle switch" in our brains doesn't work as well. It is not just harder to multi-task, it's also harder to switch between tasks. We have more difficulties with problem solving, concentration, and certain kinds of decisions. Our knowledge base and life experience, of course, continue to increase, often compensating for these changes, but neurologists now have little doubt that there are changes in the activation of the prefrontal cortex of the brain.

In younger people, activation of the prefrontal cortex during "higher level" intellectual activity tends to be localized. Brain scans show lighting up on just the left side or just the right side of the brain. When neuroscientists look at the brains of people who are over the age of 40 performing mental tasks, however, they often see activation on both sides of the brain. The lessening of "asymmetrical activation" in the brain seems to indicate that more brain power is needed to perform the same tasks. Neuroscientists have even invented an acronym to describe this phenomenon, HAROLD, for hemispheric asymmetry reduction in older adults.

What scientists have not known until recently was whether HAROLD could be reduced or even prevented with lifestyle changes.

Aerobic Fitness and Brain Activation

The possibility of preventing this aspect of brain aging attracted the attention of Dr. Hideaki Soya, a professor of exercise and neuroendocrinology at the University of Tsukuba in Japan. Dr. Soya and his colleagues recruited 60 Japanese men between the ages of 64 and 75 who showed no obvious signs of dementia to participate in a study.

The research team first tested the men's aerobic fitness. Then, on a follow-up visit, they fitted the men with infrared sensors that measure the flow of blood and uptake of oxygen in the brain. The volunteers were given the task of pressing buttons corresponding to a word on the screen, the name of a color, but not the color of the background of the word. For instance, if the test had been conducted in English, "G-R-E-E-N" might appear on a blue background, and the participants would be expected to press the button for green, not blue.

This task takes considerable brain power, and in younger people has been shown to light up the left side of the prefrontal cortex. When scientists have given this task to older people, they have found that the right side of the brain usually also lights up. In aerobically fit older men, however, just the left prefrontal cortex showed higher blood flow and oxygen uptake, similar to younger volunteers.

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