A walk in the park can soothe the mind and, in the process, change the workings of human brains in ways that improve mental health, according to a new study.
Most Americans live in cities and spend far less time outside in green spaces than people did several generations ago. City dwellers also have a higher risk for anxiety, depression and other mental illnesses than people living outside urban centers, studies show.
These developments seem to be linked, at least to some extent, according to a growing body of research. Various studies have found that urban dwellers with little access to green spaces have a higher incidence of psychological problems than people living near parks and that city dwellers who visit natural environments have lower levels of stress hormones immediately afterward than people who have not recently been outside.
But just how a visit to a park or other green space might alter mood has been unclear. Does experiencing nature actually change our brains in some way that affects our emotional health?
That possibility intrigued Gregory Bratman, a graduate student at the Emmett Interdisciplinary Program in Environment and Resources at Stanford University, who has been studying the psychological effects of urban living. In a study published last month, he and his colleagues found that volunteers who walked briefly through a lush, green portion of the Stanford campus were more attentive and happier afterward than volunteers who strolled for the same amount of time near heavy traffic.
But that study did not examine the neurological mechanisms that might underlie the effects of being out in nature.
RUMINATION
So for the new study, which was published July 14 in Proceedings of the National Academy of Sciences, Bratman and his collaborators decided to scrutinize what effect a walk might have on a person's tendency to brood.
Brooding, which is known among cognitive scientists as morbid rumination, is a mental state in which people can't seem to stop chewing over the ways in which things are wrong with themselves and their lives. This broken-record fretting is neither healthy nor helpful. It can be a precursor to depression and is disproportionately common among city dwellers compared with people living outside urban areas, studies suggest.
Perhaps most interesting for the purposes of Bratman and his colleagues, however, such rumination also is strongly associated with increased activity in part of the brain -- the subgenual prefrontal cortex. If the researchers could track activity in that part of the brain before and after people visited nature, Bratman realized, they would have a better idea about whether and to what extent nature changes people's minds.
Bratman and his colleagues first gathered 38 healthy, adult city dwellers and asked them to complete a questionnaire to determine their normal level of morbid rumination.
The researchers also checked for brain activity in each volunteer's subgenual prefrontal cortex, using scans that track blood flow through the brain. Greater blood flow to parts of the brain usually signals more activity in those areas.
Then the scientists randomly assigned half of the volunteers to walk for 90 minutes through a leafy, quiet, parklike portion of the Stanford campus or next to a loud, hectic, multilane highway in Palo Alto, Calif. The volunteers were not allowed to have companions or listen to music. They were allowed to walk at their own pace.
STILL BROODY
Immediately after completing their walks, the volunteers returned to the laboratory and repeated the questionnaire and the brain scan.
As might have been expected, walking along the highway had not soothed people's minds. Blood flow to their subgenual prefrontal cortex was still high, and their broodiness scores were unchanged.
But the volunteers who had strolled along the quiet, tree-lined paths showed slight but meaningful improvements in mental health, according to their scores on the questionnaire. They were not dwelling on negative aspects of their lives as much as they had been. They also had less blood flow to the subgenual prefrontal cortex. That portion of their brains was quieter.
These results "strongly suggest that getting out into natural environments" could be an almost immediate way to improve moods for city dwellers, Bratman said.
HOW AND HOW MUCH?
But of course many questions remain, he said, including how much time in nature is sufficient or ideal for mental health, as well as what aspects of the natural world are most soothing. Is it the greenery, quiet, sunniness, loamy smells, all of those, or something else that lifts people's moods? Must they walk or otherwise be physically active outside to gain the fullest psychological benefits? Should they be alone or could companionship amplify mood enhancements?
"There's a tremendous amount of study that still needs to be done," Bratman said.
But in the meantime, he noted, there is little downside to strolling through the nearest park, and some chance that you might beneficially muffle, at least for a while, your subgenual prefrontal cortex.
ActiveStyle on 08/17/2015