Getting close to nature has a positive impact on brain regions involved in stress processing.
In a study of healthy adults, researchers observed a decrease in activity in the amygdala after a 1-hour walk in the forest, but not after a stroll on a busy city street.
“The results support the previously assumed positive relationship between nature and brain health, but this is the first study to prove the causal link,” study investigator Simone Kühn, PhD, head of the Lise Meitner Group for Environmental Neuroscience, Max Planck Institute for Human Development, Berlin, Germany, said in a news release.
“Interestingly, the brain activity after the urban walk in these regions remained stable and did not show increases, which argues against a commonly held view that urban exposure causes additional stress,” Kühn added.
The study was published online Sept. 5 in Molecular Psychiatry.
Stresses of City Living
Urban living can be stressful and has been linked to an increased risk for mental health disorders including depression, anxiety, and schizophrenia.
Conversely, there is a “solid body of research showing that nature is beneficial for mental health, but no study so far has examined neural mechanisms lying behind the stress-relieving effects of nature,” lead author Sonja Sudimac, also with the Max Planck Institute, told Medscape Medical News.
The researchers assessed changes in stress-related brain regions after a 1-hour walk on a busy shopping street in Berlin vs a 1-hour walk in Grunewald forest.
They measured brain activation in 63 healthy volunteers, before and after the walk, using a fearful faces task and a social stress task.
They found that amygdala activation decreased after the nature walk but remained stable after the walk in an urban environment.
“Interestingly, we observed this in both functional magnetic resonance imaging tasks, which suggest that a walk in nature may have had a global beneficial effect on the amygdala by increasing its threshold for activation,” Sudimac told Medscape Medical News.
The findings are in line with a 2017 study by the same researchers.
In that study, city dwellers who lived close to a forest had a physiologically healthier amygdala structure and were therefore presumably better able to cope with stress.
“The findings highlight the importance of creating more green areas in cities. Since more than half of the world population lives in cities and urbanization is rapidly increasing, it is crucial for urban dwellers to have a nearby park or a forest where they can restore or ‘recharge’ from [the] stressful urban environment,” Sudimac said.
Green Cities for Mental Health
Reached for comment, Sebastian Ocklenburg, PhD, with MSH Medical School Hamburg, University of Applied Sciences and Medical University, Hamburg, Germany, said the study is “interesting and newsworthy.”
What is “most noteworthy,” Ocklenburg told Medscape Medical News, is that the researchers were able to pinpoint the positive effects of nature on the brain through decreased activity in the amygdala, which is “crucial for [the] processing of fear and stress in the brain.”
“Such neuroscience studies are crucial for getting an understanding of the involved mechanisms and goes a step beyond behavioral studies that just show increased well-being after hiking, etc,” Ocklenburg said.
“It implies that living in a more rural environment with lots of nature could be beneficial for mental health, as long as you actually spend time in nature. For urban planners it suggests to plan cities as green as possible and integrate parks and forests, etc,” he added.
Funding was provided by Projekt DEAL. The authors and Ocklenburg disclosed no relevant conflicts of interest.
Mol Psychiatry. Published online September 5, 2022. Full text.
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