PLAYGROUND USE BUILDS LAB MICE'S BRAIN CELLS.

Byline: Associated Press 

Young mice living in a miniature playground built up a startling increase in brain cells, suggesting sports and challenging classes could do the same for kids as late as high school, a researcher says.

Experts said the study is the first demonstration that a stimulating environment can boost the number of brain cells in a mammal, but researcher Fred Gage cautioned that the effect in mice has not yet been shown in humans.

When the experiment began, the mice were 21 days old, which corresponds roughly to teen-age years in people.

The study, appearing in Thursday's issue of the journal Nature, suggests environment might continue to have a dramatic effect on brain development long after preschool, when it has gotten the most attention.

Gage, of the Salk Institute for Biological Studies in La Jolla, Calif., said the mice showed a 15 percent increase in cells at one brain site, compared with rodents not exposed to the playground.

``We were not expecting this big of an effect,'' Gage said.

The brain site, in the hippocampus, is involved in learning and memory. Mice that spent three months in the playground also did better at a test of learning than other mice, but it's unclear whether the extra brain cells were the reason.

Janice Juraska, a University of Illinois psychology professor who studies brain development in rats, said prior work had shown that a stimulating environment can increase the number of connections between brain cells in rodents. By actually boosting the number of brain cells, ``you're not stuck with the old circuits. You can start afresh,'' she said.

Heather Cameron, a brain researcher at the National Institute of Neurological Disorders and Stroke, said men and women probably do make new brain cells in that region. But there's no evidence that building up a greater number of brain cells there does any good, she said.

What's more, the average person already lives in a more stimulating environment than lab mice do, so it's not clear whether further improvement would make any difference in brain cell numbers, she said.

The researchers used 24 female mice. Half spent three months in a special playground cage, while the others stayed in regular cages.

In the special cage, which held 12 animals at once, mice could scurry through plastic tubes and a tunnel with several openings, and run on an exercise wheel. They got to forage for treats such as cheese, crackers, apples and popcorn.

The standard cages, which were smaller and held four mice apiece, contained a water bottle and a food tray so mice could eat and drink when they wanted to.