Experiment shows what 1 hour in nature does to the human brain: ScienceAlert

Human history has largely unfolded in bucolic settings, with sprawling savannahs and forested river valleys where our ancestors lived for millions of years.

By comparison, cities represent a radically new kind of habitat that, despite its many benefits, often impairs our mental health. Research has linked urban environments to an increased risk of anxiety, depression and other mental health problems, including schizophrenia.

Fortunately, research also hints at a solution: visiting wildlife, even briefly, is associated with a number of mental and physical health benefits, including lower blood pressure, less anxiety and depression, improved mood, better concentration, better sleep , better memory and faster healing.

Numerous studies have confirmed this correlation, but we still have a lot to learn. Can a simple walk in the woods really cause all these beneficial changes in the brain? And if so, how?

A 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 shows that the amygdala is less activated during stress in rural residents than in urban residents, but this does not necessarily mean that rural life causes this effect. Perhaps, on the contrary, and people who have this trait from nature, most likely, will live outside the city.

To answer this question, researchers at the Max Planck Institute for Human Development developed a new study, this time using functional magnetic resonance imaging (MRI).

Using 63 healthy adult volunteers, researchers asked subjects to fill out questionnaires, complete working memory tasks and undergo fMRI scans while answering questions, some of which were designed to induce social stress. Participants were told that the study involved MRI and walking, but they did not know the purpose of the study.

The subjects were then randomly assigned to take a one-hour walk in an urban environment (Berlin’s busy shopping district) or in a natural environment (3,000 hectares of Berlin’s Grünewald forest).

The researchers asked them to walk a certain route anywhere, without veering off course or using their mobile phones. After the walk, each participant underwent another fMRI scan with an additional stress-inducing task and completed another questionnaire.

Researchers report that fMRI scans showed a decrease in amygdala activity after a walk in the woods, supporting the idea that nature can have beneficial effects on areas of the brain associated with stress. And apparently, it can happen in just 60 minutes.

“The results confirm a previously hypothesized positive link between nature and brain health, but this is the first study to prove a causal link,” says environmental neuroscientist Simone Kühn, chair of the Lisa Meitner Environmental Neuroscience Group at the Max Planck Institute for Humanity development.

Participants who walked in the forest also reported more attention recovery and more enjoyment from the walk itself than those who walked in the city, a finding consistent with the fMRI study as well as previous research.

The researchers also learned something interesting about the test subjects who were walking around the city. While their amygdala activity didn’t decrease like those who walked in nature, it also didn’t increase despite spending an hour in a busy urban environment.

“This strongly suggests a salutogenic effect of nature as opposed to an urban effect that causes additional stress,” the researchers write.

Of course, this doesn’t mean that being in cities can’t cause stress, but it can be a positive sign for city dwellers. Perhaps the effect of stress is less strong or widespread than other studies show, or perhaps it depends on certain factors that were not present on that Berlin street.

In any case, a new study offers some of the strongest evidence yet for this brain activity associated with stress can be reduced take a walk in the nearby forest, as our ancestors might have done.

The study was published in Molecular psychiatry.

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