Igusa, known scientifically as Juncus effusus L. var. decipiens Buchen., is the core material used in making tatami mats. After the grass is cultivated, it is dried and woven into mats, which are then sewn onto the tatami base. The material has been a fixture of Japanese architecture for centuries, and its scent defines the atmosphere of the Washitsu, the Japanese-style room with floor-level furniture and sliding wood-and-paper doors. Despite this deep cultural embedding, the researchers point out that very little scientific evidence has existed to support the widespread belief that the smell of Igusa promotes comfort and relaxation. Over ninety percent of the Igusa grown in Japan comes from a single region, Yatsushiro City in Kumamoto Prefecture on the island of Kyushu, making the crop both an agricultural specialty and a cultural touchstone.

Associate Professor Kuniyoshi Shimizu of Kyushu University’s Faculty of Agriculture, who led the study, explained that the scent of Igusa is associated in Japan with comfort and relaxation, but that scientific support for such claims has been scarce. His team has been applying objective scientific methods to investigate the effects of Igusa on people, and their earlier work demonstrated that the aromatic compounds in Igusa have relaxing effects. Building on that foundation, the researchers set out this time to explore other potential benefits, including mood, stress resilience, and task engagement, moving beyond simple relaxation to examine how the material might influence mental performance under demand.

The experimental design was deliberately straightforward but carefully controlled. Volunteers were placed in a soundproof room under two conditions: in one, they sat on Igusa mats, and in the other, they sat on unscented polypropylene plastic mats that served as the control. While seated, the participants completed simple tasks, and the research team measured both their reaction times and their brain activity using an electroencephalograph, commonly known as an EEG. This technique records electrical signals produced by the brain through electrodes placed on the scalp, allowing researchers to track different frequency bands of neural oscillations that are associated with distinct cognitive states. After the sessions, the team administered psychological questionnaires to assess the volunteers’ stress levels and sense of comfort.

The study involved a total of seventeen volunteers with an average age of 21.5 years. When the team compared task performance on the Igusa mat with the control condition, they observed a significant difference. The EEG recordings showed that when participants were sitting on the Igusa mats while completing their tasks, they exhibited increased beta wave activity in certain regions of the brain. Beta waves are typically associated with active concentration and alert mental processing, so this pattern indicated that the participants had enhanced focus and better cognitive engagement with the tasks at hand when in contact with the natural material.

Beyond the beta wave findings, the researchers documented additional neural signatures that pointed toward a broader psychological benefit. Under the Igusa mat condition, gamma wave activity showed clear changes between resting and task periods across many areas of the brain. Gamma oscillations are the fastest brain waves and are thought to reflect coordinated information processing across neural networks. Meanwhile, alpha wave activity, which is generally linked to relaxed wakefulness, remained more stable during rest periods when participants were on the Igusa mats. Taken together, the team interpreted these patterns as evidence of increased stress resilience achieved through more efficient relaxation, meaning that participants appeared to reach and maintain a restful state more effectively while still being able to engage fully when tasks demanded attention.

The subjective reports from the volunteers aligned with the physiological data in an important way. After using the Igusa mats, participants reported reduced tension and anxiety. However, not every dimension of mood shifted: other aspects of mood showed no significant change between conditions. This specificity is notable, because it suggests that the material’s effect is not a blanket emotional alteration but rather a targeted influence on tension, anxiety, and the neural machinery of attention. The combination of reduced anxiety with heightened beta wave engagement presents an interesting picture, since relaxation and alertness are often treated as opposing states, yet the data suggest they can coexist under the right conditions.

The researchers are careful to frame this study as a first step rather than a definitive conclusion. With only seventeen participants, the sample was small, and the team acknowledges that the next step is to replicate the experiment with a larger and more diverse population. Furthermore, the study evaluated only short-term responses, so the long-term effects of regular Igusa use remain an open question. The crossover design of the study, in which each participant experienced both the Igusa and control conditions, strengthens the internal validity of the findings, but broader generalization will require the expanded trials the team has planned. These caveats are standard for exploratory psychophysiological research and do not diminish the significance of obtaining objective, instrument-based evidence for a phenomenon previously supported only by anecdote and tradition.

The implications of the work extend in two directions at once. For science, the study contributes new empirical data on the potential benefits of Igusa mats, specifically their capacity to reduce tension and anxiety and to support stress resilience during task performance, adding to the earlier finding that aromatic compounds in the grass have relaxing effects. For society, the research arrives at a moment when Igusa’s role in Japanese life is shrinking. Shimizu noted that for generations Igusa has brought comfort to Japanese living spaces, but that its use has decreased due to changes in lifestyles and modern housing environments. Through their research, the team hopes to deepen understanding of how traditional materials can influence people and to discover new applications for them in contemporary society, potentially giving this centuries-old agricultural product a renewed purpose in an era increasingly interested in natural materials and evidence-based wellbeing.

What makes the study particularly compelling is its methodological humility combined with its cultural resonance. Rather than relying on self-reported comfort alone, the researchers anchored their conclusions in electrophysiological measurements, capturing how the brain’s rhythm patterns shifted across rest and task states depending on the material beneath the participant. The convergence of beta wave increases during tasks, gamma wave modulation between rest and activity, stable alpha waves during rest, and questionnaire-reported reductions in tension and anxiety forms a coherent multi-level picture. As the team moves toward larger and longer-term studies, the humble rush grass woven into tatami mats may find itself repositioned from a nostalgic symbol of traditional interiors to a scientifically validated component of environments designed to support focus, composure, and resilience in modern life.

Subject of Research: Neurophysiological and psychological effects of Japanese Igusa rush grass mats on mood, stress resilience, and task engagement

Article Title: Using Japanese Igusa (rush grass) may enhance mood, stress resilience, and task engagement

Article References: Using Japanese Igusa (rush grass) may enhance mood, stress resilience, and task engagement. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: Igusa, tatami, rush grass, EEG, brain activity, stress resilience, cognitive engagement, beta waves, gamma waves, alpha waves, Kyushu University, Scientific Reports