How Nature Nurtures: Amygdala activity decreases as a result of a one hour walk in Nature.
An article on Nature.com
Sudimac, S., Sale, V. & Kühn, S. How nature nurtures: Amygdala activity decreases as the result of a one-hour walk in nature. Mol Psychiatry 27, 4446–4452 (2022). https://doi.org/10.1038/s41380-022-01720-6
Abstract:
Since living in cities is associated with an increased risk for mental disorders such as anxiety disorders, depression, and schizophrenia, it is essential to understand how exposure to urban and natural environments affects mental health and the brain.
It has been shown that the amygdala is more activated during a stress task in urban compared to rural dwellers.
However, no study so far has examined the causal effects of natural and urban environments on stress-related brain mechanisms.
To address this question, we conducted an intervention study to investigate changes in stress-related brain regions as an effect of a one-hour walk in an urban (busy street) vs. natural environment (forest).
Brain activation was measured in 63 healthy participants, before and after the walk, using a fearful faces task and a social stress task.
Our findings reveal that amygdala activation decreases after the walk in nature, whereas it remains stable after the walk in an urban environment.
These results suggest that going for a walk in nature can have salutogenic effects on stress-related brain regions, and consequently, it may act as a preventive measure against mental strain and potentially disease.
Given rapidly increasing urbanization, the present results may influence urban planning to create more accessible green areas and to adapt urban environments in a way that will be beneficial for citizens’ mental health.
Introduction:
The human brain is shaped by its surroundings. Increasing urbanization has been one of the recent major changes in our environment, resulting in more than half of the world’s population currently living in cities, projected to increase to 68% by 2050
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. In a seminal cross-sectional study, the amygdala has been shown to be more activated during a social stress task in urban compared to rural dwellers . Nevertheless, intervention studies are needed to demonstrate the causal effects of natural and urban environments on the brain. In a single functional magnetic resonance imaging (fMRI) intervention study conducted so far it was shown that a 90-minute walk in nature decreased self-reported rumination and activity in the subgenual prefrontal cortex (sgPFC), associated with rumination, whereas there was no change after the urban walk .
However, to the best of our knowledge, there has been no fMRI intervention study examining the causal effects of exposure to urban vs. natural environments on stress-related brain regions. And importantly, the previous findings do not disentangle whether stress-relief after being in nature is the result of exposure to the natural environment itself or merely of the absence of detrimental urban effects. To address these questions, we conducted an fMRI intervention study investigating brain activity before and after a one-hour exposure to natural versus urban environments. We hypothesized that stress-related brain regions would be less activated after exposure to the natural compared to the urban environment, relative to the baseline activation before the walk. A-priori defined and preregistered (https://aspredicted.org/tm629.pdf) brain regions of interest (ROI) included amygdala, anterior cingulate cortex (ACC), and dorsolateral prefrontal cortex (dlPFC).
You can read the full study here: https://www.nature.com/articles/s41380-022-01720-6