Neuroscience of Gardening: Mycobacteria and Serotonin

Gardeners have long claimed that working with plants is their therapy. While the fresh air and physical activity certainly help, modern microbiology has uncovered a fascinating, microscopic reason why getting your hands in the dirt improves your mood.

Mycobacterium vaccae and the Brain

The soil is teeming with microscopic life. One specific, harmless bacterium found in common dirt is Mycobacterium vaccae.

When gardeners dig in the soil, they inhale or ingest trace amounts of this bacterium. Research conducted by neuroscientists at the University of Bristol found that exposure to M. vaccae acts similarly to an antidepressant. When injected into mice, the bacterium stimulated a specific group of neurons in the brain that produce serotonin.

The Serotonin Boost

Serotonin is the neurotransmitter primarily responsible for regulating mood, anxiety, and happiness. The exposure to this soil bacterium led to increased serotonin release in the prefrontal cortex, resulting in decreased anxiety and improved cognitive function in the test subjects.

This biological interaction suggests that humans evolved a symbiotic relationship with the earth. Being separated from the microbiome of the soil by concrete and asphalt may deprive our brains of a natural, evolutionary trigger for serotonin production. Gardening is a way to biohack that connection.