Physiological effects of touching sugi (Cryptomeria japonica) with the palm of the hand

Abstract

Abstract Wood is used as an interior material in Japan, and it is empirically known that contact with wood induces relaxation in humans. However, evidential data regarding these physiological effects are lacking. In this study, we examined the physiological effects of tactile stimulation based on measurements of brain and autonomic nervous activities by using the wood of sugi (Cryptomeria japonica). Twenty-one female university students (mean age, 22.0 ± 2.0 years) participated in the study. Oxyhemoglobin (oxy-Hb) concentrations in the prefrontal cortex were determined using near-infrared time-resolved spectroscopy. High frequency (HF), denoting parasympathetic nervous activity, and the ratio of low frequency (LF)/(LF + HF), indicating sympathetic nervous activity, were measured using heart rate variability. HF (0.15–0.40 Hz) and LF (0.04–0.15 Hz) components were calculated by the maximum entropy method. The wood material surfaces were finished by: (1) brushing with a stainless steel wire brush and (2) sanding with a belt sander. A marble plate served as a comparator. The palm of each participant’s right hand touched each material for 90 s. Touching brushed or sanded sugi significantly decreased oxy-Hb concentrations in the left and right prefrontal cortices, increased ln(HF), and decreased the ln(LF/(LF + HF)) ratio compared with touching marble. Thus, our findings indicate that compared with touching marble, touching sugi with the palm induces physiological relaxation, as indicated by calmer prefrontal cortex activity, higher parasympathetic nervous activity, and lower sympathetic nervous activity.