[Oct 3, 2022: Maria Einhorn, Max Planck Institute for Human Development]
Living close to nature is largely beneficial for mental health and the brain. (CREDIT: Creative Commons)
Living in a city is a well-known risk factor for developing a mental disorder, while living close to nature is largely beneficial for mental health and the brain. A central 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.
Even though urbanization has many advantages, living in a city is a well-known risk factor for mental health . Mental health problems like anxiety, mood disorders, major depression, and schizophrenia are up to 56% more common in urban compared to rural environments.
It has been suggested that urban upbringing is the most important environmental factor for developing schizophrenia, accounting for more than 30% of schizophrenia incidence. Since there is a consistent dose-response relationship between schizophrenia and urban environment, even when controlling for possible confounders such as sociodemographic factors, family history, drug abuse, and size of social network, the hypothesis is that urban environment is related to higher schizophrenia incidence through increased social stress.
On the other hand, exposure to nature provides attentional restoration and stress relief. The biophilia hypothesis states that humans feel an innate tendency to connect with nature since this attitude is rooted in our evolutionary history.
Research about the beneficial effects of nature has been mainly motivated by two theoretical frameworks − Attention Restoration Theory (ART) and Stress Recovery Theory (SRT), that explain the psychological benefits of nature from different perspectives. ART focuses on cognitive restoration through nature exposure. The notion is that nature invokes involuntary attention allowing voluntary attention processes to recover. SRT, on the other hand, emphasizes affective responses in contact with nature, that lead to restoration.
According to SRT, the restorative process is related to the stress-reducing capacity of natural environments that involves an increase in positive emotions as well as a decrease in arousal and negative emotions such as fear.
A growing body of empirical research has demonstrated the cognitive and affective benefits of exposure to natural environments. Spending time in nature can improve working memory capacity, restore directed attention as well as reduce negative emotions and stress. The evidence of nature’s beneficial effects on stress has been observed not only in psychological assessments, but also in physiological indicators of stress, namely in decreases in heart rate, blood pressure, and stress-related hormone cortisol.
Even though the beneficial effects of nature exposure have been repeatedly shown, the neural underpinnings of these effects are unknown.
“But so far the hen-and-egg problem could not be disentangled, namely whether nature actually caused the effects in the brain or whether the particular individuals chose to live in rural or urban regions”, says Sonja Sudimac, predoctoral fellow in the Lise Meitner Group for Environmental Neuroscience and lead author of the study.
To achieve causal evidence, the researchers from the Lise Meitner Group for Environmental Neuroscience examined brain activity in regions involved in stress processing in 63 healthy volunteers before and after a one-hour walk in Grunewald forest or a shopping street with traffic in Berlin using functional magnetic resonance imaging (fMRI).
The results of the study revealed that activity in the amygdala decreased after the walk in nature, suggesting that nature elicits beneficial effects on brain regions related to stress.
“The results support the previously assumed positive relationship between nature and brain health, but this is the first study to prove the causal link. 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,” explains Simone Kühn, head of the Lise Meitner Group for Environmental Neuroscience.
The authors show that nature has a positive impact on brain regions involved in stress processing and that it can already be observed after a one-hour walk. This contributes to the understanding of how our physical living environment affects brain and mental health.
Even a short exposure to nature decreases amygdala activity, suggesting that a walk in nature could serve as a preventive measure against developing mental health problems and buffering the potentially disadvantageous impact of the city on the brain.
The results go in line with a previous study (2017, Scientific Reports) which showed that city dwellers who lived close to the forest had a physiologically healthier amygdala structure and were therefore presumably better able to cope with stress.
Before the walk participants filled out questionnaires and underwent the fMRI scanning procedure, which included the Fearful Faces Task and the Montreal Imaging Stress Task. Subsequently, each participant was randomly assigned to a 60-min walk, in either a natural or urban environment. After the walk, the participants underwent the fMRI scanning procedure again and filled out the questionnaires. (CREDIT: Molecular Psychiatry (Mol Psychiatry))
This new study again confirms the importance for urban design policies to create more accessible green areas in cities in order to enhance citizens’ mental health and well-being.
In order to investigate benedicial effects of nature in different populations and age groups, the researchers are currently working on a study examining how a one-hour walk in natural versus urban environments impacts stress in mothers and their babies.
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Note: Materials provided above by Max Planck Institute for Human Development. Content may be edited for style and length.
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