A 60-minute walk in a natural setting has been shown to quiet the activity in a structure of the brain known to have a significant role in the processing of stress. This is a finding in a new study reported by the Lise Meitner Group for Environmental Neuroscience at the Max Planck Institute for Human Development, Berlin, Germany.
It has been established that living within a city is a significant risk factor for developing a disorder of mental health. A centrally-located structure in the brain – the amygdala – is known to be the main processor of stress, evidenced by an increase in activity. The same stress, experienced by people in rural areas, is less activating of the amygdala.
“But so far the hen-and-egg problem could not be disentangled, namely whether nature actually causes the effects in the brain or whether the particular individuals chose to live in rural or urban regions,” says study leader Sonja Sudimac, a predoctoral fellow in the Lise Meitner Group, in a statement.
The researchers examined brain activity during stress processing in 63 healthy volunteers, before and after a one-hour walk in either Grunewald Forest or an urban street with traffic in Berlin. Activity was measured during functional magnetic resonance imaging (fMRI). These brain scans reveal that activity in the amygdala decreased after the walk in the forest, suggesting that nature elicits beneficial effects on brain regions which process 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,” explains Simone Kühn, head of the Meitner Group for Environmental Neuroscience. “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.”
The authors show that nature’s favorable effect on stress processing can be observed after a one-hour walk. This contributes to understanding how our environment affects the brain and mental health. Even a short exposure to nature decreases amygdala activity, suggesting that nature walks could serve as a preventive measure against city dwellers developing mental health disorders.
The researchers are currently conducting a study examining how a one-hour walk in rural versus urban environments affects stress in mothers and their infants.
Their study is published in the journal Molecular Psychiatry.
Comment from Dr. Faith Coleman:
Kühn said, “This is the first study to prove the causal link.” It is more common than is justified for an author to claim their work is a ‘first.’ I sometimes check that:
City Life Affects Brain’s Response to Stress – WebMD (Published: Jun 23, 2011)
As they were stressed, people who were currently living in cities had more activity in an almond-shaped area of the brain called the amygdala than those who lived in towns or rural areas.
“Causal” requires vigorous proof, which is lacking here. The author weakens her argument for causality in the next sentence, when results deviated from the expected: “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.”
Also negating the claim of causality is the statement of Sonja Sudimac: “… namely whether nature actually causes the effects in the brain or whether the particular individuals chose to live in rural or urban regions.”
As always, BrainTomorrow encourages readers to consider the evidence and interpret it as they will.