Dirt good for brain, study says

Parents, here's another reason for your kids to play outdoors in the dirt: It may make them smarter.

And, as a side benefit, dirt appears to be a natural anti-anxiety drug, but without the side-effects.

Mice exposed to a bacterium found in soil navigated a maze twice as fast, and with less anxiety, as control mice, in studies presented Monday at the 110th general meeting of the American Society for Microbiology in San Diego.

The researchers say we've become so urbanized we risk losing a connection with an organism in nature that may actually be beneficial to humans.

Dr. Dorothy Matthews became intrigued by Mycobacterium vaccae -- a natural soil microbe -- in 2007, when British scientists published a study showing when mice were injected with a heat-killed version of the organism, it stimulated neurons in the brain stem to start producing serotonin.

"Serotonin is a molecule that has a number of different effects, but one of them is modulating mood and decreasing anxiety," says Matthews, an associate professor of biology at The Sage Colleges in Troy, NY.

Serotonin also plays a role in learning. "If you're nervous, if you're frightened, you just can't think straight," Matthews said. She wondered, could M. vaccae have an effect on learning in mice?

She and her colleague, Dr. Susan Jenks, also a professor of biology, dabbed the bacteria onto tiny peanut butter sandwich squares made with Wonder bread. "I thought, 'What's a super-absorbent bread?" Matthews said.

In one experiment, they tested how long the mice took to navigate a maze, which illustrates how quickly the rodents were learning whether they needed to turn right, or left.

The bacteria-exposed mice consistently ran the maze twice as quickly as the non-exposed mice. They also showed fewer anxiety behaviours -- less freezing, wall-climbing, stopping and grooming, returning to the start, or defecation.

In other words, they were not scared poop-less.

Next, the researchers removed the bacteria from the peanut butter treats. About one week out, the mice started running the mazes more slowly than they did when they were ingesting the bacteria. "They experienced a kind of serotonin withdrawal," Matthews said. They were still faster than the controls, on average, an effect that lasted for another month of testing.

After a three-week rest, the bacteria-exposed mice still ran the maze faster than the control mice, but the difference was no longer statistically significant, suggesting the effect is temporary.

-- Canwest News Service

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