In evolutionary terms, human physiology, which has evolved in response to the natural environment, has had little time to adapt to the artificial environments of urban areas. According to a United Nations report, 30% of the world’s population in 1950 was urban population, and this value is projected to rise to 66% by 2050. However, since the industrial revolution, an increasing number of people have moved from natural to artificial urban environments. Human physiological functions have adapted to the natural environment over 6–7 million years of human evolution. The findings of this study demonstrated that forest-derived auditory stimulation induced physiological and psychological relaxation effects. Exposure to the forest sound resulted in the following significant differences compared with exposure to city sound: decreased oxy-Hb concentrations in the right prefrontal cortex decreased ln(LF/HF) decreased heart rate improved feelings described as “comfortable,’’ “relaxed,” and “natural” and improved mood states. Subjective evaluation was performed using the modified semantic differential method and profiles of mood states. Heart rate, the high-frequency component of heart rate variability (which reflects parasympathetic nervous activity), and the ratio of low-frequency to high-frequency (LF/HF) components (which reflects sympathetic nervous activity) were measured.
Oxyhemoglobin (oxy-Hb) concentrations in the prefrontal cortex were determined by near-infrared spectroscopy. A total of 29 female university students (mean age 22.3 ± 2.1 years) were exposed to high-resolution sounds of a forest or city for 60 s, using headphones.
This study examined prefrontal cortex and autonomic nervous activities in response to forest sound. Exposure to natural sounds is known to induce feelings of relaxation however, only few studies have provided scientific evidence on its physiological effects.
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