Microbiologists from The Sage Colleges found that mice fed Mycobacterium vaccae experienced a significant boost in physical and mental performance. Mice fed the bacteria navigated a complex maze in half the time it took for a group that did not receive the bacteria. They also showed lower levels of anxiety.

The study builds on a 2007 report from researchers in England, who observed that the bacteria injected into mice stimulated the growth of neurons in the brain, resulting in increased serotonin levels and decreased anxiety levels.

Scientists believe Mycobacterium vaccae may work in a similar way in humans, acting as an antidepressant by boosting serotonin levels.

So, do humans need to eat mud pies to get the same benefit? Not exactly. The bacteria is so common that humans are exposed to a significant amount of it each time they walk down a dirt path, perform gardening activities or simply dig around in the dirt.