TUESDAY, Sept. 20, 2005 (HealthDay News) -- Everybody knows exercise is good for your heart, but is it good for your brain?
Scientists think it is, and new evidence suggests they might be right -- at least with aging mice.
The researchers, who report their findings in the Sept. 21 issue of The Journal of Neuroscience, discovered that a small number of mice that exercised regularly appeared to be mentally sharper than those that were the rodent equivalents of couch potatoes.
The tests suggest that exercise helps generate new brain cells, even in mice that have reached the late stages of their lives, said study co-author Fred Gage, a researcher at the Salk Institute for Biological Studies in La Jolla, Calif.
Previous research has shown that younger mice placed in an "enriched environment" -- one with plenty of stimulation -- were better at learning than other mice, Gage said. The new study was designed to figure out the role of exercise.
Researchers gathered 15 mice that were "young" (3 months old) and 18 that were "old" (19 months old). Mice have an average lifespan of 26 months, so the older mice were roughly 60 to 65 years old in human terms, Gage said.
The researchers then divided the mice into different groups. Some were placed in cages with a wheel and walked two to four kilometers a day for 45 days; others had no chance to exercise. The researchers then tested the mental agility of the mice by putting them through a maze.
The older mice that exercised did a better job navigating the maze than the sedentary older mice. Apparently, exercise wakes up dormant areas of the brain that begin creating new brain cells, Gage said.
In fact, later analysis revealed that the older but active mice actually reversed their neuronal decline -- growing up to 50 percent more new neurons compared with their younger but inactive peers. These new brain cells appeared to function just as well as those grown by younger mice, the researchers add.
Years ago, scientists assumed that brain cells -- called neurons -- didn't grow after childhood; if they died, they were gone forever. But over the past several years, researchers have found evidence that neurons can regenerate after all.
It isn't clear what the new study means for people, especially older folks who might wonder if a walk around the block will help keep them sharp. For one thing, the mice happily exercised; unlike humans, they didn't ignore the running wheels -- or put them in the garage, Gage said.
"Most animals, when given an opportunity, will choose an environment that allows them to move around," he said, adding, that many people are the exact opposite.
Still, a growing body of research has linked exercise to improved mental abilities in both animals and humans, Gage said. Future research will use MRI scanners to examine what's taking place in the brain during exercise, he said.
The mental effects of exercise are indeed a mystery, said Dr. James Grisolia, a neurologist at Scripps Mercy Hospital in San Diego, especially when compared to what doctors know about how physical activity improves heart-lung function, blood pressure, muscle tone and our sense of well-being.
However, if you aren't exercising as much as you should, don't be too worried about your neurons, Grisolia said.
"Mental exercise and stimulation are even more important than exercise to prevent Alzheimer's disease in humans, so this should not be neglected," he said. "Crossword puzzles, adult extension courses, reading and other challenging 'thinking' projects can all help preserve quality of life into old age."
For more on exercise for seniors, visit the National Library of Medicine.