That, of course, raises the question of why they don't perform better mentally. No one knows for sure at this point, because no one knows the "functional significance of the new neurons and BDNF," Rhodes says.
In other words, no one knows exactly what that stuff is supposed to do.
But it seems likely that both are facilitators for learning, and part of the experiment supports that. In addition to the hyperactive mice, the researchers also had a bunch of "normal" mice that spent a reasonable amount of time on the running wheel, because all rodents like to run on a wheel, but they weren't addicted to it.
The normal mice also increased their good chemicals and grew new neurons while exercising, and they also improved their ability to learn how to get through a maze.
So a normal level of exercise does help in learning, at least for a mouse.
Exercise in Moderation
What does it all add up to?
"What our study basically confirms is normal exercise is good for the brain and enhances learning," Rhodes says. "But when you take an animal that is running three times as much as normal, an exercise addict, that actually has a negative effect."
Of course, it's possible that the reason the hyperactive mice performed so poorly in the mental test has nothing to do with brain chemicals or new neurons. Maybe, Rhodes speculates, they just couldn't think about anything but running.
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.