Natural environments are known to provide mental health benefits.
For example, being around nature can reduce negative emotions and stress. On the flip side, psychologists have long contended a connection between urban living and poor mental health. For example, city dwellers have higher rates of anxiety, depression, mood disorders, and schizophrenia than people living in rural areas. With increasing urbanization, it is important to consider how natural versus city environments may impact the brain. There is evidence that city dwellers show greater activation of the amygdala during social stress tasks compared to rural dwellers.
“There has been solid research showing that exposure to nature is beneficial for mental health and cognition, but no study so far has examined neural mechanisms lying behind these effects,” explained Sudimac (@SSudimac), a PhD student at the Max Planck Institute for Human Development in Berlin.
“In a seminal study, a brain region involved in stress processing, the amygdala, is less activated during stress in people who live in rural areas, compared to those who live in cities, hinting at the potential benefits of nature. But so far it was not possible to disentangle the hen-and-egg problem, namely whether nature caused the effects in the brain or whether the particular individuals chose to live in rural or urban regions.”
“That is why we conducted an intervention study in which we managed to show the causal evidence — namely, amygdala activity remained stable after a walk in urban environment, while a walk in nature markedly reduced amygdala activity,” Sudimac explained.
This specific study was based in Berlin.
A total of 63 subjects with an average age of 27 were recruited from Berlin to participate in the experiment. Roughly half the sample was randomly assigned to take an hour-long walk through an urban forest in Berlin, while the other half was assigned to take an hour-long walk through a busy street in one of Berlin’s city centers. Before and after the walk, participants had their brains scanned as they went through social stress tasks (a face-to-face discussion with someone about a difficult topic) and facial emotion recognition tests that measured amygdala activity in response to fearful or neutral facial expressions.
The results revealed that participants who went on the nature walk showed decreased amygdala activity following the walk, during both the fearful faces task and the social stress task. Those who walked in the city showed stable amygdala activity during the two tasks. The study’s authors suggest that exposure to nature promotes recovery from stress by lowering amygdala activity.
Exposure to urban environments, on the other hand, neither decreases nor increases amygdala activity.
We predicted that a walk in nature would decrease amygdala activity, while a walk in an urban environment would increase it,” Sudimac said. “However, it surprised us that a walk in the city did not cause additional stress-related brain activity. The brain activity in these regions remained stable after the urban walk, which argues against a commonly held view that urban exposure causes additional stress.”
Interestingly, results from the fearful faces task were consistent for both masked and unmasked faces — amygdala activity decreased after the nature walk and remained stable after the city walk for both types of faces. These findings suggest that people can be unaware of nature’s stress-reducing effects even when consciously aware of an influence, as with masked faces.
“Going for a walk in nature is beneficial for our mental health and brain,” Sudimac told PsyPost. “Even though many studies have shown that nature is good for our well-being, we found for the first time a causal link between exposure to nature and a reduction of stress-related brain activity. Interestingly, this effect was found only after a one-hour walk, so if one doesn’t have time to spend a whole day in nature, it looks that only one hour is beneficial for our brain.”
Sudimac’s study found that spending more time in nature might increase the amygdala’s threshold for activation, leading to reduced amygdala activity during stress. This means that exposure to nature could potentially buffer the negative impact of urban living and lower the risk of mental disorders among city dwellers. The study authors recommend urban planning should include efforts to modify and design cities with better access to green spaces to protect and improve mental health of residents.
“We hope with our study to raise awareness about the importance of accessible green areas in cities,” Sudimac said.
For future research…
The task for future research might be, for example, to hone in on the sights, sounds, and smells that reduce amygdala activity. Studies could also compare the effects of particular types of natural environments, such as urban parks versus botanical gardens.
Could a habit of walking through nature be proven to boost resiliency in even those with the highest levels of anxiety?
“We are also interested in different populations and age groups and we are currently analyzing the data from our last study on how a one-hour walk in natural versus urban environments impact stress in mothers and their babies,” Sudimac said.
“I would like to add that these findings are also important because they confirm the importance of accessible green environments in cities,” she continued. “Since more than half of the world population lives in cities and urbanization is rapidly increasing, urban dwellers must have a nearby park or a forest where they can restore or ‘recharge’ from the stressful urban environment. With our research, we aim to draw attention to the importance of the presence of nature in urban environments and to provide evidence for urban design policies to create more green areas in cities that would be accessible to all citizens to enhance their mental health and well-being.”
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