Most of human history has taken place in idyllic settings, with sweeping savannahs and forested river valleys that have sheltered our ancestors for millions of years.
In comparison, cities represent a radically new place to live that, despite its many benefits, often takes a toll on our sanity. Research has linked urban environments to an increased risk of anxiety, depression and other mental health problems, including schizophrenia.
Fortunately, research also points to a solution: Visiting the wild, even for a short time, is linked to a number of mental and physical health benefits, including lower blood pressure, less anxiety and depression, improved mood, better focus , better sleep, better memory and more faster healing.
Numerous studies support this connection, but we still have a lot to learn. Can a walk in the woods really trigger all of these positive brain changes? And if so, how?
A good place to look for clues is in the amygdala, a small structure in the center of the brain involved in stress processing, emotional learning, and the fight-or-flight response.
Research shows that the amygdala is less activated during stress in rural people than in city dwellers, but that doesn’t necessarily mean that living in the country causes this effect. Maybe it’s the opposite, and people who have this trait naturally are more likely to live in the countryside.
To investigate this question, researchers at the Max Planck Institute for Human Development have developed a new study, this time using 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 aimed at inducing social stress. Participants were told the study included an MRI and a walk, but they were unaware of the purpose of the research.
The subjects were then randomly assigned to a one-hour walk in either an urban setting (a busy shopping district in Berlin) or a natural setting (Berlin’s 3,000-hectare Grunewald forest).
The researchers asked them to walk a specific route in both locations without deviating from the course or using their mobile phones. 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, supporting the notion that nature can trigger beneficial effects in brain regions related to stress. And apparently it can happen in as little as 60 minutes.
“The results support the previously assumed positive connection between nature and brain health, but this is the first study to prove the causal connection,” says environmental neuroscientist Simone Kühn, head of the Lise Meitner Group for Environmental Neurosciences at the Max Planck Institute for Human Sciences Development.
Participants who took a forest walk also reported greater recovery of attention and more enjoyment from the walk itself than those who took city walks, a result consistent with the results of the fMRI study as well as previous research.
The researchers also learned interesting things about subjects who went for walks in the city. While their amygdala activity did not decrease as in those who took nature walks, it did not increase either after spending an hour in a busy urban environment.
‘This strongly supports nature’s salutogenic effect, in contrast to urban exposure, which causes additional stress,’ the researchers write.
Of course, that doesn’t mean that city exposure can’t cause stress, but it can be a positive sign for city dwellers. Perhaps the stress effect is less powerful or pervasive than other studies suggest, or perhaps it depends on certain factors that weren’t present on this Berlin street.
In any case, the new study offers some of the clearest evidence yet Stress-related brain activity can be reduced by take a walk through a nearby forest, just as our ancestors might have done.
The study was published in Molecular Psychiatry.
