Visiting Nature for Mental Health

A Stanford University study has found that spending time in verdant, natural spaces positively affects the way our brains work. Walking yields many health benefits due in part to its simplicity and sustainability due to moderate effort, but now research suggests spending less time on the treadmill and more time exploring the great outdoors delivers added bonuses. It seems there is yet another reason to walk long distances—and to do so in as natural a setting as possible.

Other studies have found that city dwellers with little contact with green spaces have higher incidences of depression, anxiety and other psychological problems than people living near parks. Monitoring stress hormone level immediately after people spend time outside shows that such contact with the natural world seems to lower those stress hormones.

The latest research indicates that experiencing nature actually may change our brain chemistry in ways directly tied to emotional health. The controlled experiment looked at whether nature would influence rumination, defined as repetitive thoughts that focus on negative aspects of the self. This is a known risk factor for mental illness. 

Participants who went on a 90-minute walk through a natural environment reported lower levels of rumination and showed reduced neural activity in the subgenual prefrontal cortex, an area of the brain linked to risk for mental illness, compared with those who walked through an urban environment. By separating the benefits of walking from the benefits of walking in nature, the researchers have discovered an important new component to improved mental health: green spaces.

The study's 38 participants were adult city dwellers who were asked to complete a questionnaire to determine their normal level of morbid rumination. Brain activity in the subgenual prefrontal cortex was also measured.

Half of these subjects were then randomly assigned to walk for 90 minutes through a leafy and quiet area of the Stanford University campus. The other half were asked to walk near a loud multi-lane highway in Palo Alto.

The subjects then repeated both the questionnaire and the brain scan. Walking along the highway did nothing to diminish activity in the subgenual prefrontal cortex.

But the volunteers who assigned to walk along the tree-lined paths on campus showed meaningful improvements in their mental health questionnaire scores. They also had less blood flow to the subgenual prefrontal cortex.

More than 50% of people now live in urban areas. By 2050, that level is estimated to reach 70%. It is therefore important to allot space for parks in cities, and for people living in urban settings to carve out time to regularly visit them.

PNAS, 2015, Vol. 112, No. 28, pp. 8567–8572, http://www.pnas.org/content/112/28/8567.abstract

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