- Living in cities has been associated with higher rates of mental health disorders.
- A new study has found that a 60-minute walk in nature decreases activity in brain regions involved in processing stress.
- Brain activity in these regions remained stable after a 60-minute walk in an urban setting.
Several studies have found higher rates of major mental illnesses in urban areas compared to rural areas.
A 2012 meta-analysis, for example, found an increased risk of schizophrenia for those who live in cities.
Other research, including this one
In a new study, researchers from the Lise Meitner Group for Environmental Neuroscience at the Max Planck Institute for Human Development in Germany explored the benefits of nature on mental health.
The researchers investigated whether higher rates of mental illness in urban areas were linked to individuals having less access to nature, or whether certain types of people are attracted to certain environments.
The results of the study were recently published in the journal
To determine their hypothesis, the researchers examined the brain activity of 63 healthy participants using functional magnetic resonance imaging (fMRI) before and after the participants took an hour-long walk in a forest or a shopping street with traffic.
Study participants included 29 women and 34 men between the ages of 18 and 47. The average age was 27 years old. Each participant received an fMRI. During the scans, they had several exercises for the participants, two of which were discussed in the study.
In the first exercise, participants saw images of 15 male faces and 15 female faces representing fearful and neutral facial expressions. In the second exercise, participants were given mental arithmetic tasks “with a time limit designed to be just beyond the participant’s cognitive abilities,” the study paper explains.
After completing the scans, 31 participants were assigned a walk down a busy Berlin street, while 32 walked through an urban forest. Participants walked in 2019 between 10 a.m. and 5 p.m. Men and women were equally divided into the two groups.
Researchers gave participants a phone to wear on their walk that kept track of their location. Participants also wore wristbands that monitored their electrodermal activity (EDA), heart rate variability (HRV), and heart rate. They were given a lunch bag that they could eat during the march. After 30 minutes of walking, a telephone alarm went off signaling that it was time to turn around.
After the participants finished their walks, the researchers gave them another fMRI while having them perform the same exercises.
“The results of our study show that after only [a] 1 hour of walking in nature, activity in brain regions involved in processing stress decreases,” Sudimac said.
“This is an important finding as it demonstrates for the first time a causal relationship between exposure to nature and change in stress-related brain regions.”
– Sonja Sudimac, lead author of the study
The researchers observed a decrease in activity during the two exercises undertaken during the analysis. This suggests, Sudimac said, that “nature walking may have had an overall beneficial effect on the amygdala by increasing its activation threshold.”
Additionally, brain activity in regions involved in stress processing remained stable and did not increase after a 60-minute walk in an urban setting. This goes against the idea that urban exposure causes additional stress, according to Sudimac.
Research shows that nature walks “could serve as a preventive measure against the development of mental health problems” and “mitigate the negative effects of [the] urban environment on mental health,” according to Suidimac.
She hopes this type of research will also help planners make the inclusion of accessible green environments in cities a priority.
“As more than half of the world’s population lives in cities and urbanization is increasing rapidly, it is crucial for city dwellers to have a nearby park or forest where they can [recharge] of [the] stressful urban environment,” said Suidimac DTM.
Given that scans showed reduced activity in brain regions involved in processing stress after an hour-long walk in nature, could shorter walks also be beneficial?
“We chose the 1 hour duration because more than that could have been tiring for some participants who are not used to physical exercise,” says Sudimac.
“There is evidence that physiological indicators of stress, such as the stress hormone cortisol, are lower after – a 15-minute walk in nature compared to a walk in an urban environment, so it would be interesting to examine whether shorter exposure to nature also decreases amygdala activity.
Karen Stewart, an Alabama-based clinical psychologist not involved in the study, warned that there may be another explanation for the decreased activity in brain regions involved in processing stress in participants who experienced did a one hour nature walk, other than theory they were responding to the green environment.
“It’s too early to claim that’s a definitive explanation,” she said. DTM.
Perhaps, Stewart said, the decrease could come from the positive effects of physical exercise.
The reason that scans of participants who walked down a busy street did not show decreased activity in brain regions involved in processing stress, she added, could be because “The negative effects of the urban environment negate the benefits of exercise.”
The researchers acknowledge that this study relied on a “WEIRD” sample – or participants who were mostly Western, educated, industrialized, wealthy and Democratic.
With future efforts, however, the researchers plan to include participants from other ethnic groups and cultures “not only to make the results more generalizable, but also to examine cultural differences in the experience of nature, because what is considered as nature also differs from culture to culture”, Sudimait says DTM.
With other future efforts, researchers hope to examine the impact of different natural environments, such as rivers, botanical gardens and mountains, on the brain.
They would also like to work to be able to identify specific attributes of nature – certain colors, sounds or smells – that lead to decreased activity in the amygdala “to understand why nature recovers from stress and, therefore, to make nature-based therapy more effective,” Sudimac said.
Currently, researchers are working to examine how an hour-long walk in nature compared to urban environments affects stress in mothers and their babies.