The majority of people now live in cities, and spend much less time enjoying nature than people did in previous generations. Research shows urban dwellers are at higher risk for anxiety, depression and other mental illnesses, compared to people living in rural environments. Now a new study has proven that walking in nature actually changes your brain.
A growing body of research has demonstrated that residents of cities who have limited access to green spaces have higher levels of psychological problems than people who live near parks. Other research shows that city residents who visit natural environments have lower levels of stress hormones, when their levels are measured immediately afterward, than do people who have not been out in nature.
Until recently, however, we did not understand the mechanism by which being in nature lowered stress levels. That mechanism intrigued Gregory Bratman, a graduate student at the Emmett Interdisciplinary Program in Environment and Resources at Stanford University. Bratman has been focusing on the psychological effects of urban environments on residents.
In an earlier study published last month, he and his team found that volunteers who took a walk through a lush, green natural area of the Stanford campus were happier and more attentive, compared to other volunteers who walked near heavy traffic. But the study did not explore the neurological processes that are triggered by exposure to nature.
In his new study, published last week in Proceedings of the National Academy of Sciences, Bratman and his team decided to examine the effects of a nature walk on an individual’s tendency to brood. Brooding, which cognitive scientists call morbid rumination, is a state of worry that can sometimes lead to depression. It is disproportionately common among urban dwellers compared with people who live outside cities.
Scientists know that morbid rumination is also strongly linked to increased activity in the portion of the brain known as the subgenual prefrontal cortex. The researchers decided if they could track activity in that area of the brain, they would be able to better understand the physiology involved.
Bratman and his colleagues enlisted 38 healthy adult urban residents, and had them complete a questionnaire to assess their normal level of morbid rumination. They checked for brain activity by tracking the blood flow through the brain. Higher blood flow to any area of the brain indicates increased activity in that area.
Half the participants were randomly assigned to walk for 90 minutes through a quiet, leafy natural portion of the Stanford campus, while the others were assigned to walk next to a loud, busy multi-lane highway in Palo Alto. The participants walked alone with out music, at their own chosen pace.
As soon as they had completed their walks, the participants returned to the laboratory and repeated both the questionnaire and the brain scan. As you might imagine, the volunteers who walked along the highway did not find the experience relaxing. Their broodiness scores remained the same, and the blood flow to their subgenual prefrontal cortex remained high.
Conversely, the volunteers who had walked through nature showed small but significant improvements in their mental health as measured by the scores on the questionnaire. They were worrying less. They also experienced less blood flow to the subgenual prefront cortex, demonstrating that portion of their brains were quieter.
Bratman says the data “strongly suggest that getting out into natural environments” can be a quick and easy way to immediately improve mood for city dwellers.