Physiological and Psychological Effects of Forest and Urban Sounds Using High-Resolution Sound Sources

• Published in: International journal of environmental research and public health Vol. 16; no. 15; p. 2649
• Main Authors: Jo, Hyunju, Song, Chorong, Ikei, Harumi, Enomoto, Seiya, Kobayashi, Hiromitsu, Miyazaki, Yoshifumi
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 24.07.2019; MDPI
• Subjects: Acoustics; Adult; Autonomic Nervous System - physiology; Blood flow; Brain; Cerebral blood flow; Cities; Cortisol; Emotions; Environmental effects; Female; Forests; Headphones; Heart Rate; Humans; I.R. radiation; Infrared spectra; Infrared spectroscopy; Levels; Maximum entropy method; Measuring instruments; Near infrared radiation; Oxygen consumption; Oxyhemoglobins - analysis; Parasympathetic nervous system; Perfusion; Physiological effects; Physiology; Prefrontal cortex; Prefrontal Cortex - metabolism; Psychological effects; Relaxation; Researchers; Sound; Sound sources; Spectrum analysis; Stress; Studies; Urban areas; Urban environments; Urban populations; Values; Young Adult; Cities; Japan; autonomic nervous activity; profile of mood states; prefrontal cortex activity; heart rate; near-infrared spectroscopy; semantic differential method; heart rate variability; natural sound; physiological relaxation effects; forest sound
• ISSN: 1660-4601; 1661-7827; 1660-4601
• DOI: 10.3390/ijerph16152649

Exposure to natural sounds is known to induce feelings of relaxation; however, only few studies have provided scientific evidence on its physiological effects. This study examined prefrontal cortex and autonomic nervous activities in response to forest sound. 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. Oxyhemoglobin (oxy-Hb) concentrations in the prefrontal cortex were determined by near-infrared spectroscopy. 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. Subjective evaluation was performed using the modified semantic differential method and profiles of mood states. 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. The findings of this study demonstrated that forest-derived auditory stimulation induced physiological and psychological relaxation effects.