Our progress as a species has been largely the result of our ability to get and use the resources that planet Earth has to offer. Apparently, we use 1/3 to 1/2 of what the global ecosystem produces. These fragile ecosystems provide us with clean water, medicines, food, recreational pursuits, and also help regulate our climate. Exposure to nature also provides an environment that contributes to our health and cognitive abilities. Recent research has demonstrated that when our attentional resources are depleted, a walk in nature restores those resources more significantly than a walk in an urban environment. It has also been suggested that exposure to nature improves our health beyond the benefits of exercise and fresh air. I was curious as to whether anyone had explored what effects may occur on the nervous system.
Recently, a team of researchers from Japan and Korea looked at the effects of exposure to nature versus an urban environment on heart rate variability. Heart rate variability is a method used to assess autonomic nervous system activity. The autonomic nervous system has two parts. The sympathetic nervous system (SNS) engages in emergency situations when you need energy quickly, so your heart rate and breathing rates go up. The parasympathetic nervous system (PNS) engages to slow down energy use, to help restore energy and improve healing. The use of heart rate variability takes advantage of the fact that the connections between the SNS and our various organs is loose, whereas the connections between the PNS and those organs is tight. The large gap at the SNS connections means the signal will begin more slowly and take longer to turn off. The tight connections of the PNS allows for quicker turning on and off. So if the heart rate is fluctuating rapidly or at a high frequency (HF) it is probably because of PNS activation, whereas if it is fluctuating relatively slowly or at a low frequency (LF) it is probably because of SNS activation. The larger the HF contribution, the better your health. Research has demonstrated a relationship between your hearts LF/HF ratio and your health. In general, the lower the ratio the better your health.
Lee and his colleagues exposed subjects to either a forest or urban environment for 15 min. They found that as a result of forest exposure the high-frequency component of HRV increased and the LF/HF ratio decreased at the time of the exposure. This suggests that the PNS was activated during forest exposure and that the SNS was less activated. The results support the concept that exposure to nature has positive effects on physical health. It is snowing now, I am going to go for a walk.
Source: Lee, J., Park, B. -J, Tsunetsugu, Y., Ohira, T., Kagawa, T., and Miyazaki, Y. (2011) Effect of forest bathing on physiological and psychological responses in young Japanese male subjects. Public Health, 125, 93-100.
Other resources: Hansen-Ketchum, P. A., & Halpenny, E. A. (2011). Engaging with nature to promote health: bridging research silos to examine the evidence. Health Promotion International, 26(1), 100 –108. ; Berman, M. G., Jonides, J., & Kaplan, S. (2008). The Cognitive Benefits of Interacting With Nature. Psychological Science, 19(12), 1207 –1212.
