Because humans have lived and adapted to their natural environment for the past 5 million years, it is deduced that humans function most optimally in natural environments such as the forest. It is from this philosophy that the Japanese concept and practice of Shinrin-yoku derived, defined as “making contact with nature and taking in the atmosphere of the forest.”
The 1990s brought about the new term “technostress,” describing the noticeably increased levels of workload and stress. Research supports that the more humans are exposed to nature, the more physiological benefits they receive. Ulrich’s 1981 research showed that subjects exposed to more nature scenes experienced a decrease in blood pressure, higher alpha brainwave amplitudes, and reduced muscle tension.
This study measures the physiological benefits of nature through two variables: (1) brain activity (by measuring the absolute hemoglobin concentration) in the region of the brain called the “prefrontal cortex”, and (2) the cortisol levels in saliva. The prefrontal cortex is responsible for generating higher-level executive thoughts. Cortisol is a hormone produced by the body to fight stress. Therefore, measuring activity of the prefrontal cortex helps scientists understand how a subject’s thoughts are changing, and measuring cortisol levels helps to understand the amount of stress the body is experiencing.
The results of this study show that both cerebral activity and cortisol levels lowered significantly, indicating that subjects experienced the relaxing effects of Shinrin-yoku.
The purpose of this study is to examine Shinrin-yoku’s (walking in the forest, watching forest landscapes) physiological and psychological effects on people.
The study took place in the Seiwa Prefectural Forest Park in Japan. The subjects consisted of 12 male college students around 23 years old. The physiological indicators measured were salivary cortisol levels, to indicate stress levels, and the absolute hemoglobin concentration, to indicate level of brain activity. The subjects reported having no physiological or psychological disorders. The environmental conditions (space, meals, temperature, humidity) were controlled to eliminate variability in unrelated environmental conditions.
The subjects were divided into two groups of six. On each day, one group spent their day in the forest and the other group spent the day in the city. On the second day, the groups switched between the nature and city conditions. Each day was broken up into four parts: the morning at the accommodations, the forenoon walking around their condition area for 20 minutes, the afternoon sitting observing their condition area for 20 minutes, and the night time back at the accommodations. The morning and evening in the accommodations were used as control environments to compare to the forest/urban conditions.
Measurements were taken one person at a time of the prefrontal cortex activity and salivary cortisol levels. The measurements were taken six times a day: once in the morning at the accommodations before heading out for the day, two in the forenoon, two in the afternoon, and one more when returning to the accommodations at night. The two measurements taken in the forenoon were right before going for a walk, and right after completing the 20-minute walk. The two measurements taken in the afternoon were right before sitting to observe their condition area and one right after completing the 20-minute observation period.
Saliva was collected in a salivette for five minutes, and the absolute hemoglobin concentrations of the prefrontal cortex were measured using the “A Time-Resolved Spectroscopy” (TRS) system. Sensory evaluation was conducted after physiological measurements at each of the six measurement times throughout the day. Subjects were asked to measure their level of “comfort” and “calm” on 13-point Likert scales. The results were analyzed using a one-tailed t-test to analyze the physiological effect and a Wilcoxon signed rank test to analyze the psychological effects.
After walking and watching, subjects were significantly more “comfortable” in the forest than in the city. There were no significant differences between the forest and city “comfort” levels in the morning or evening. Calmness and comfortability showed the same trends.
t-Hb measurements showed that absolute t-Hb levels were significantly decreased in forest areas over city areas.
t-Hb levels were significantly lower in forest area walkers than in city area walkers.
Salivary cortisol levels were significantly lower before and after watching the forest area compared to watching the city area. In psychological testing, forest settings were significantly more comfortable and calmer than city settings.
t-Hb measurements cannot be taken under bright sunshine, so there were several cases when data could not be gathered in both the city and forest settings.