Abstract
In Japanese households, it is customary to walk barefoot on wood floors. This study sought to clarify the physiological effects produced via tactile application of sugi (Cryptomeria japonica) to the sole of the feet, using the brain and autonomic nervous activities as indicators. Twenty-seven female university students (mean age, 21.9 ± 1.9 years) participated in this study. Oxy-hemoglobin (oxy-Hb) concentrations in the prefrontal cortex were determined using near-infrared time-resolved spectroscopy. High frequency (HF), denoted parasympathetic nervous activity, and low frequency (LF)/HF indicated sympathetic nervous activity; both were measured using heart rate variability. The wooden material was unpainted sugi wood with two different finishes uzukuri brushing or sanding. A similarly sized marble plate served as a control. The sole of the feet of each participant touched each material for 90 s. The results found that the uzukuri wood significantly decreased oxy-Hb concentration in the left prefrontal cortex compared with touching the marble. Furthermore, compared to before contact, the uzukuri wood showed significantly decreased oxy-Hb concentrations in the right prefrontal cortex, increased ln(HF), and decreased the ln(LF/HF) ratio. Moreover, the contact with sanded wood significantly decreased oxy-Hb concentrations in the right prefrontal cortex compared with before contact. Thus, it is concluded that tactile application of sugi to the sole of the feet induced physiological relaxation.
Highlights
Modern society today is stressful [1, 2]; there is a growing interest in the relaxation effects of naturederived stimuli [3, 4]
The oxy-Hb concentrations during contact with the uzukuri wood were lower than the concentrations before tactile stimulation and generally took 81 s to return to this state (Fig. 4a, line of brown)
This study found that tactile stimulation to the sole of the feet induced by touching sugi with the uzukuri finish resulted in calmer left prefrontal cortex activity as compared with contact with marble
Summary
Modern society today is stressful [1, 2]; there is a growing interest in the relaxation effects of naturederived stimuli [3, 4]. “Uzukuri finish” is a finishing method for coniferous materials such as sugi or hinoki. This finishing method involves scraping off the soft earlywood part with a brush and leaving an embossed hard latewood part exposed [15]. This processing makes the wood-grain standout and emphasizes the feel specific to this wood. We investigated the effects of sole of the feet contact with the uzukuri finished hinoki wood on brain activity and autonomic nervous activity in the previous study [16]. Contact with uzukuri finish hinoki for 90 s decreased the prefrontal cortex activity, increased parasympathetic nervous activity, and decreased sympathetic nervous activity compared to the marble, control, which is a common building material
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