Laboratory mice treated with friendly bacteria normally found in soil (Mycobacterium vaccae) activated a group of neurons that produce the brain chemical serotonin - altering behavior like antidepressant drugs.

When the team looked closely at the brains of mice, they found that treatment with M. vaccae activated a group of neurons that produce the brain chemical serotonin.

The lack of serotonin in the brain is thought to cause depression in people, thus M. vaccae's effects on the behavior of mice may be due to increasing the release of serotonin in parts of the brain that regulate mood.

Such were the findings of University of Bristol researchers published in the latest issue of Neuroscience.

According to the paper's lead author, Dr. Chris Lowry:

"These studies help us understand how the body communicates with the brain and why a healthy immune system is important for maintaining mental health. They also leave us wondering if we shouldn't all be spending more time playing in the dirt."

And that's probably why we turn into little kids when we play in the mud and enjoy the act tremendously.

Read the full report.