Effects of Listening to Forest Sound and Viewing Forest Video on Prefrontal Cortex and Autonomic Nervous Activity

This study aimed to assess the effects of Listening to forest sounds and viewing forest videos on the prefrontal cortex and autonomic nervous activity. Oxy-hemoglobin (oxy-Hb) levels were determined using near-infrared spectroscopy as an indicator of prefrontal cortex activity. Heart rate variability (HRV) was used as an indicator of autonomic nervous activity. The natural logarithmic high-frequency component (LnHF) of HRV, which reflects parasympathetic nervous activity, and the natural logarithmic ratio of low-frequency and high-frequency components (LnLF/HF), which reflects sympathetic nervous activity, were measured. The general emotion scale was used to assess emotions. Overall, 21 healthy male and female participants were recruited for this study. All subjects were exposed to forest sounds, forest videos, and urban videos in a random order. Comparisons of oxy-Hb levels in the prefrontal cortex among the three conditions revealed a significant decrease while listening to the forest sound (p=0.004, p=0.005). Furthermore, a significant decrease in oxy-Hb levels was observed during forest sound exposure compared with that after exposure (p=0.000). No significant differences in HRV were found among the three conditions and within each condition. In terms of the general emotion scale, exposure to forest sounds and videos significantly increased “Calmness” scores. Moreover, significantly improved scores of the scale item “Negative Affect” were observed with the forest video. These results suggest that forest sounds induced a significant reduction in oxy-Hb concentrations in the prefrontal cortex and that forest sounds and videos enhance a state of subjective calmness after exposure.