Human history has unfolded largely in bucolic settings, with sprawling savannas and forested river valleys hosting our ancestors for millions of years.
By comparison, cities represent a radical new kind of habitat, one that despite its many perks often strains our mental health. Research has linked urban environments with increased risk for anxiety, depression, and other mental health problems, including schizophrenia.
Fortunately, research also hints at a solution: Visiting wilderness, even briefly, is associated with an array of mental and physical health benefits, including lower blood pressure, reduced anxiety and depression, improved mood, better focus, better sleep, better memory, and faster healing.
Numerous studies have supported this correlation, but we still have a lot to learn. Can just walking in a forest really spark all these beneficial changes in the brain? And if so, how?
One good place to look for clues is the amygdala, a small structure in the center of the brain involved in stress processing, emotional learning, and the fight-or-flight response.
Research indicates the amygdala is less activated during stress in rural residents versus city dwellers, but that doesn’t necessarily mean rural living causes this effect. Maybe it’s the opposite, and people who naturally have this trait are more likely to live out in the country.
To address that question, researchers from the Max Planck Institute for Human Development devised a new study, this time with help from functional magnetic resonance imaging (fMRI).
Using 63 healthy adult volunteers, the researchers asked subjects to fill out questionnaires, perform a working memory task, and undergo fMRI scans while answering questions, some of which were designed to induce social stress. Participants were told the study involved MRI and going on a walk, but they didn’t know the goal of the research.
The subjects were then randomly assigned to take a one-hour walk in either an urban setting (a busy shopping district in Berlin) or a natural one (Berlin’s 3,000-hectare Grunewald forest).
Researchers asked them to walk a specific route in either location, without going off-course or using their mobile phones along the way. After their walk, each participant took another fMRI scan, with an additional stress-inducing task, and filled out another questionnaire.
The fMRI scans showed reduced activity in the amygdala after a walk in the woods, the researchers report, which supports the idea that nature can trigger beneficial effects in brain regions involved with stress. And apparently it can happen in just 60 minutes.
“The results support the previously assumed positive relationship between nature and brain health, but this is the first study to prove the causal link,” says environmental neuroscientist Simone Kühn, head of the Lise Meitner Group for Environmental Neuroscience at the Max Planck Institute for Human Development.
Participants who took a forest walk also reported more attention restoration, and more enjoyment of the walk itself than those who took urban walks, a finding consistent with the study’s fMRI’s results as well as previous research.
The researchers also learned something interesting about subjects who took urban walks. While their amygdala activity didn’t decrease like those who took nature walks, it also didn’t increase, despite having spent an hour in a busy urban setting.
“This strongly argues in favor of the salutogenic effects of nature as opposed to urban exposure causing additional stress,” the researchers write.
That doesn’t mean urban exposure can’t cause stress, of course, but it may be a positive sign for city dwellers. Maybe the stressing effect is less potent or pervasive than other studies suggest, or maybe it depends on certain factors that weren’t present on that Berlin street.
In any case, the new study offers some of the clearest evidence yet that stress-related brain activity can be reduced by taking a stroll through a nearby forest, just like our ancestors might have done.
The study was published in Molecular Psychiatry.