Can Playing in the Dirt Make You Smarter?

First posted on 06-24-2010

Not all bacteria in dirt is bad. Scientists are discovering that a specific bacteria in soil, already believed to lower depression and anxiety, can also help human learning abilities.

“Mycobacterium vaccae is a natural soil bacterium which people likely ingest or breath in when they spend time in nature,” says Dorothy Matthews of The Sage Colleges in Troy, New York, who conducted the research with her colleague Susan Jenks. They presented their findings recently at the 110th General Meeting of the American Society for Microbiology in San Diego.

Earlier studies demonstrated that M. vaccae, when heat-killed and injected into mice, stimulated the growth of neurons in the brain while increasing serotonin levels and decreasing anxiety.

“Since serotonin plays a role in learning we wondered if live M. vaccae could improve learning in mice,” Matthews said.

So Matthews and Jenks decided to feed their mice live M. vaccae bacteria before sending them through a maze. They also sent a control group of mice through the same maze, but did not feed them bacteria.

“We found that mice that were fed live M. vaccae navigated the maze twice as fast and with less demonstrated anxiety behaviors as control mice,” according to Matthews.

As a means of verifying their findings, Matthews and Jenks withheld M. vaccae from the experimental group’s diet and tested the mice again by sending them through the maze. They navigated the maze slower than they had after ingesting M. vaccae, but still faster than their counterparts in the control group.

Finally, Matthews and Jenks gave the experimental group a three week rest before testing them a a final time. The experimental group of mice continued to outperform the control group, but at a rate reduced enough to indicate that the effects of M. vaccae are temporary.

“This research suggests that M. vaccae may play a role in anxiety and learning in mammals,” says Matthews. “It is interesting to speculate that creating learning environments in schools that include time in the outdoors where M. vaccae is present may decrease anxiety and improve the ability to learn new tasks.”

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