Exercise-Crazed Mice Are Poor Thinkers

Oct. 9 -- Exercise may improve our brains as well as our bodies, but it's possible to get too much of a good thing.

Those characters who become so addicted to exercise that they don't seem to know how to stop may actually be impairing their brain's ability to learn new tasks.

That's no excuse to stay on the couch, according to the lead author of a series of new studies showing that exercise increases the chemicals in the brain that help brain cells communicate with each other. It also helps the brain grow new neurons in the region known as the hippocampus, which controls learning and memory.

So Justin Rhodes, a neuro-scientist at the Oregon Health & Science University in Portland was a bit surprised when his data showed that mice that had become addicted to exercise had a terrible time finding their way through a maze. Other mice that exercised at a "normal" level breezed through the test with no problems. The researchers report their findings in two current professional journals, Neuroscience, and Behavioral Neuroscience.

Born to Run

Since the hyperactive mice were creating new neurons and producing more of the "good chemical" that the brain needs to function properly, called "BDNF (brain derived neurotrophic factor) it seems logical that they would also learn how to get through the maze better than the couch potatoes. But they didn't.

The finding raises as many questions as answers, and there's no real evidence yet that humans experience the same mental impairment from addictive exercise as mice, but Rhodes believes that's probably the case.

"All we know is mice," he says. But, he adds, earlier research at the Salk Institute in San Diego found that humans also produce more BDNF and generate new neurons when they exercise, just like mice. So it's not much of a leap to conclude that too much exercise might also impair mental abilities in humans, just as it does in mice.

But it's worth noting that the mice that Rhodes has been studying for years now are real nut cases. They are so addicted to exercise that they run three times as much on a running wheel as normal mice.