This is not an “eat dirt for your health and happiness” study. You don’t need to shovel soil in your mouth. Just go outside.

Biologist Dorothy Matthews and company wanted to test a particular bacteria, Mycobacterium vaccae. It’s found commonly in the soil and carried widely through the air, so if you take a walk in the park you’ll probably breathe it in. Previous studies have shown that the bacterium increases serotonin in the brain, and have even suggested that the bacterium has antidepressant qualities. Since the neurotransmitter serotonin is also involved in cognition, the team wanted to see if the bacterium could have a direct effect on learning. Indeed it did, Matthews’ team announced at the General Meeting of the American Society for Microbiology in San Diego.

In a classic test of learning ability, Matthews gave mice a treat – white bread with peanut butter – as a reward to encourage them to learn to run through a maze. When she laced the treat with a tiny bit of Mycobacterium vaccae, she found that the mice ran through the maze twice as fast as mice that were given plain peanut butter [New Scientist].

The uptick in learning ability lasted as long as the researchers kept giving their mice the laced peanut butter.

But here’s a caveat: When they tested bacteria-fed mice three weeks after removing the single-cell organisms from their diet they found that these mice were still faster than the mice who never received the bacteria. The difference, however, was not significant. So the results are temporary [Scientific American].

And this is just a mouse model, too, so take that for what you will. But the least it’s another blow struck for the good name of bacteria, for the hygiene hypothesis, and for going outside, Matthews says.

“It just shows that we evolved with dirt as hunter-gatherers,” she says. “So turn off your TV and go work in your garden, or walk in the woods” [New Scientist].

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Image: iStockphoto