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.

This study aimed to clarify the effects of watching forest videos on prefrontal cortex activity. We examined oxy-hemoglobin (oxy-Hb) levels in the prefrontal cortex using near infrared spectroscopy (NIRS) and measured the changes in relaxation level using the rating scale of emotion as defined in terms of relaxation (RE scale), and the free description data after watching the videos. We recruited 21 healthy female university students for this study. All subjects watched a forest video and an urban video in a random order; no significant differences were found in comparisons between the two conditions during and after watching the videos. Comparisons of oxy-Hb levels in the prefrontal cortex during and after watching the two videos showed a significant increase after watching the forest video. Significantly decreased scores of three RE scale items, i.e., “anxiety-relief,” “restrictive-free,” and “discomfort-comfort,” were observed with the urban video. The forest video significantly improved scores of the following items: “feeling high-stable,” “tense-relaxing,” “anxiety-relief,” “restrictive-free,” and “discomfort-comfort.” These results suggest that the forest video activates the left prefrontal cortex and subjectively enhances a relaxed feeling, after watching.