Research shows that city living is associated with increased levels of mental illness, including depression. Exposure to nature, on the other hand, has been shown repeatedly to reduce stress and boost well-being. But no one has really been sure why. A group of researchers from Stanford University thought nature’s positive effect on our well-being might have something to do with reducing rumination, or “a maladaptive pattern of self-referential thought that is associated with heightened risk for depression and other mental illnesses.” In simpler terms, rumination is when you can’t stop thinking about things that are really bothering  you. Rumination seems to originate in the subgenual prefrontal cortex of our brains, which is the part of the brain that regulates negative emotions.

In their study, published in Proceedings of the National Academy of Sciences, the Stanford scientists examined whether a nature walk could reduce rumination in 38 mentally healthy, city-dwelling people. Half of the study subjects took a 90-minute walk through grassland dotted with oak trees and shrubs, and the other half walked along a four-lane, traffic-logged street in Palo Alto. At the end of the study, the nature walkers showed decreases in rumination and in activity in their subgenual prefrontal cortices. The urban walkers showed no such improvements.

The scientists believe nature reduces rumination by providing “positive distractions,” similar to having a hobby or chatting with a friend. Natural environments are more restorative, the authors write, and thus confer greater psychological benefits. According to the authors, this effect should work with many types of natural landscapes, particularly those that engender “soft fascination,” a “sense of belonging,” and the “sense of being away.”
Source: Khanzan O. How walking in nature prevents depression. The Atlantic. June 30, 2015.