A new study published in the journal Molecular Psychiatry offers evidence that a simple walk through nature can lower activity in stress-related brain regions. The experiment revealed that participants who walked for an hour in a forest showed decreased amygdala activity during a stress task, while those who walked for an hour in the city did not.
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 differentially impact the brain. There is some evidence that city dwellers show greater activation of the amygdala during social stress tasks compared to rural dwellers. In light of such findings, study author Sonja Sudimac and her colleagues conducted an intervention study to investigate how a walk in nature versus the city might impact stress-related brain regions. The researchers hoped to tease apart the negative effects of urban environments and the beneficial effects of nature.
“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, has been shown to be 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 (Lederbogen et al., 2011). But so far it was not possible to disentangle the hen-and-egg problem, namely whether nature actually 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.
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 underwent functional magnetic resonance imaging (fMRI) while participating in a social stress task as well as a fearful faces task 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, however, showed stable amygdala activity during the two tasks. The study authors say these findings 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 urban environment would increase it,” Sudimac said. “However, it surprised us that a walk in 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. Masked faces are stimuli designed to be processed outside participants’ awareness, so these findings suggest that people can be unaware of nature’s stress-reducing effects.
“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. It is interesting that this effect was found only after 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 and her colleagues discuss the possible implications of their study. The results suggest 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 press that urban planning should include efforts to modify and design cities with better access to green spaces in order to protect and improve the mental health of residents.
“We hope with our study to raise awareness about importance of accessible green areas in cities,” Sudimac said.
A task for future research might be to hone in on the specific aspects of nature that reduce amygdala activity — for example, sights, sounds, and smells. Studies could also compare the effects of particular types of natural environments, such as urban parks versus botanical gardens.
“We are also interested in different populations and age groups and we are currently analyzing the data from our last study 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, it is crucial for urban dwellers to have a nearby park or a forest where they can to restore or ‘recharge’ from stressful urban environment. With our research we aim to draw attention to importance of 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 in order to enhance their mental health and well-being.”
The study, “How nature nurtures: Amygdala activity decreases as the result of a one-hour walk in nature”, was authored by Sonja Sudimac, Vera Sale, and Simone Kühn.
