Thursday, September 10, 2026

AROMATHERAPY

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

EEG tests show that Igusa use is associated with increased activity in brain regions related to concentration and engagement

Kyushu University

A field of Igusa — image:
Igusa is the core material used in making tatami mats. After Igusa is cultivated, it is dried and woven into mats. These mats are then sewn onto the tatami’s base. Over 90% of Igusa grown in Japan comes from a single region: Yatsushiro City in Kumamoto Prefecture on the island of Kyushu.
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Credit: Yousuke Konno

Fukuoka, Japan—Publishing in the journal Scientific Reports, researchers at Kyushu University found that using mats made from Japanese Igusa, or rush grass, was associated with increased activity in regions of the brain related to concentration and engagement. Furthermore, surveyed participants reported reduced tension and anxiety after using Igusa mats. Igusa has been used in Japan for centuries, and the research team hopes scientific evidence on its health benefits will provide new value for this traditional material.

What is the first thing you notice when you walk into a Japanese-style room? Is it the floor-level furniture? The sliding wood-and-paper doors? Or is it the smell? Also called a tatami room—or Washitsu in Japanese—these spaces are defined by their tatami flooring, which has been part of Japanese culture and architecture for centuries. The unique smell of the Washitsu comes from the tatami, specifically the Igusa that makes up the mat surface.

“In Japan, the scent of Igusa is associated with comfort and relaxation. However, there is very little scientific evidence to support such claims,” explains Associate Professor Kuniyoshi Shimizu from Kyushu University’s Faculty of Agriculture, who led the study. “Our team has been using objective scientific methods to investigate the effects of Igusa on people. Previously, we showed that the aromatic compounds in Igusa have relaxing effects. This time we wanted to explore other benefits like mood, stress resilience, and task engagement.”

In their experimental setup, the team placed volunteers in a soundproof room under two conditions: sitting on Igusa mats or sitting on unscented polypropylene plastic mats. The volunteers then completed simple tasks while the team measured their reaction time and brain activity using an electroencephalograph (EEG). Afterward, the team conducted psychological questionnaires to assess the volunteers’ stress and comfort.

“We had a total of 17 volunteers with an average age of 21.5 years. When we compared the results of tasks performed on the Igusa mat with the control conditions, we saw a significant difference,” explains Shimizu. “The EEG results showed that when participants were sitting on the Igusa mats while completing their tasks, they had increased beta wave activity in certain parts of the brain. This indicates that they had enhanced focus and better cognitive engagement.”

Moreover, the team found that under Igusa mat conditions, gamma wave activity showed clear changes between resting and task periods across many brain areas. Alpha wave activity also remained more stable during rest periods. Together, these patterns suggest increased stress resilience through more efficient relaxation.

Afterward, volunteers reported reduced tension and anxiety after using the Igusa mats. However, other aspects of mood showed no significant change.

This study provides new empirical data on the possible benefits of Igusa mats, specifically their potential to reduce tension and anxiety as well as to support stress resilience when performing tasks.

“We had a small number of participants in this study, so the next step is to replicate the experiment with a larger, more diverse population. In addition, we only evaluated short-term responses, so we would also like to investigate the long-term effects of Igusa use,” concludes Shimizu. “For generations, Igusa has brought comfort to Japanese living spaces. But today, its use has decreased due to changes in lifestyles and modern housing environments. Through our research, we hope to deepen our understanding of how traditional materials can influence people and discover new applications for them in contemporary society.”

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For more information about this research, see "Stress resilience and engagement enhancement under the usage of Igusa (Juncus effusus L. var. decipiens Buchen.) mat: a crossover study," Fadilla Zennifa, Yanli Xu, Akiko Isa, Erika Tomimatsu, Ziyou Xu, Yousuke Konno, Masataka Ikegami, Kuniyoshi Shimizu, in Scientific Reports, https://doi.org/10.1038/s41598-026-47520-8

About Kyushu University
Founded in 1911, Kyushu University is one of Japan's leading research-oriented institutions of higher education, consistently ranking as one of the top ten Japanese universities in the Times Higher Education World University Rankings and the QS World Rankings. Located in Fukuoka, on the island of Kyushu—the most southwestern of Japan’s four main islands—Kyushu U sits in a coastal metropolis frequently ranked among the world’s most livable cities and historically known as Japan’s gateway to Asia. Its multiple campuses are home to around 19,000 students and 8,000 faculty and staff. Through its VISION 2030, Kyushu U will “drive social change with integrative knowledge.” By fusing the spectrum of knowledge, from the humanities and arts to engineering and medical sciences, Kyushu U will strengthen its research in the key areas of decarbonization, medicine and health, and environment and food, to tackle society’s most pressing issues.

Igusa is known for its unique scent that is said to have health benefits, but such claims lacked scientific evidence. Professor Kuniyoshi Shimizu from Kyushu University and his research team used EEG to monitor the brainwaves of participants while they sat on Igusa mats and completed a series of tasks. They found that when participants used Igusa mats, their brain activity showed patterns associated with increased concentration and engagement.

Credit

Yousuke Konno

Journal

Scientific Reports

DOI

10.1038/s41598-026-47520-8

Method of Research

Experimental study

Subject of Research

People

Article Title

Stress resilience and engagement enhancement under the usage of Igusa (Juncus effusus L. var. decipiens Buchen.) mat: a crossover study

Article Publication Date

8-Sep-2026

New study raises concerns about climate feedback loop as melting Arctic glaciers flush ancient methane from rocks beneath the ice

The more glaciers melt, the more methane they are likely to release

iC3 Polar Research Hub

image:
Conducting a radar survey on a Svalbard glacier during winter
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Credit: Gabrielle Kleber

Meltwater rivers flowing from Svalbard glaciers are carrying ancient methane from rocks beneath the ice into the open air, new research shows.

The findings reveal a natural feedback loop that may worsen as the Arctic continues to get warmer. Melting glaciers can open hidden pathways for methane, a powerful greenhouse gas. Put simply, the more glaciers melt, the more methane they are likely to release.

Methane in the rocks

The study was led by Gabrielle Kleber, a researcher with the iC3 Polar Research Hub in Tromsø, Norway. Her team sampled rivers draining valley glaciers across central Svalbard. They found methane in every river they tested.

The study team took 148 water samples from 19 glacier-fed rivers in central Svalbard, providing by far the most extensive assessment yet of methane in glacier meltwater in the region. Every river in their survey contained more methane than expected from contact with the atmosphere, with the highest values reaching up to 425 times that level.

Co-author Silje Waaler says the team deliberately designed the survey to capture the diversity of glaciers across the region.

“We wanted to study many different glaciers, across a range of rock types and ice conditions. That gave us a clearer picture of why some glacier rivers carry more methane than others,” she says.

A key finding is that this methane is mostly not being made by microbes under the ice, as has been observed beneath glaciers in Greenland.

Instead, it appears to come from Svalbard’s geology. Many parts of the archipelago contain old shale layers rich in organic carbon. Over millions of years, heat and pressure can turn this material into methane and other gases.

They also analysed the carbon in the methane to identify its source. In some samples, they measured related gases, including ethane and propane, which helped confirm that much of the methane came from geological sources.

“These glaciers are mostly melting on their surfaces,” Gabrielle says. “But this meltwater finds its way to the bottom of the glaciers through crevasses and holes. This means that it interacts with the rocks underneath, and where those rocks contain ancient gas, the water can flush methane out into rivers.”

The most methane-rich waters came from glaciers resting on shale-bearing rock formations. But geology alone did not explain everything.

The team also found that the physical state of the glacier bed matters. Glaciers with thawed, wet and active beds were far better at picking up methane. Glaciers frozen to their beds were less connected to the rocks below, even when methane-rich geology was present.

A map of where methane can escape

To understand these processes, the researchers combined river chemistry with ice surveys. They used ground-penetrating radar to map ice conditions within selected glaciers. This allowed them to estimate how much of each glacier bed was thawed and able to carry water.

Co-author Leonard Magerl says that this combination was crucial.

“The temperature at the base of glaciers is an important piece of the puzzle,” Leonard says. “We found that the biggest methane releases happened where the right rocks and the right glacier conditions came together. This insight can help to estimate emissions from other ice-covered regions.”

The researchers estimate that land-terminating glaciers across Svalbard may transport roughly 182 to 368 tonnes of methane per year in meltwater, depending on how the estimate is scaled. This is in addition to previous, much higher estimates for methane released by groundwater springs in front of glaciers. But it still points to a widespread and undercounted pathway for ancient carbon to reach the atmosphere.

Why this matters

Methane is a powerful greenhouse gas. While this study focuses on Svalbard, similar methane-release pathways likely occur in other glaciated regions where ice overlies organic-rich rocks or sediments. These include large parts of the Arctic, the Himalayas and Antarctica.

Gabrielle explains that: “The amounts reported here are small compared with human-caused emissions from fossil fuels, farming and waste. But they matter because they reveal a natural feedback loop that is not confined to Svalbard, and that may grow as the Arctic warms.”

As glaciers thin and retreat, more meltwater may reach their beds. This can increase contact with fractured rock, sediment and groundwater. In some places, that may flush out more methane.

However, the story is not simple. Some Svalbard glaciers are also becoming colder at their beds as they shrink. If a glacier becomes frozen to its bed, its ability to flush methane through subglacial rivers may fall.

“Our results show that future methane release will depend on both geology and glacier change,” Gabrielle says. “That makes it important to know what lies beneath the ice, not only how fast the ice is melting.”

Links to previous research

The new study builds directly on previous iC3 work on methane around retreating Svalbard glaciers. Gabrielle Kleber and Leonard Magerl have previously found that meltwater from one Svalbard glacier could carry geologic methane from beneath the ice, making it release more methane per area than Greenland glaciers. Meanwhile, newly uncovered groundwater springs are also releasing the potent greenhouse gas in Svalbard forefields, demonstrating the many understudied sources of methane in these environments.

The new study, published in Nature Communications today, takes the next step. It shows that methane-rich meltwater is not unique to one glacier. It is widespread across central Svalbard, but strongest where shale-rich geology and thawed glacier beds overlap.

Find out more

The study, “Subglacial geology and thermal conditions regulate methane emissions from Svalbard glaciers”, is published open access in Nature Communications today.

Lead researcher Dr Gabrielle Kleber and co-authors Leonard Magerl and Silje Waaler work at the iC3 Polar Research Hub, which is hosted by the Department of Geosciences of UiT The Arctic University of Norway. Gabrielle studies Arctic methane emissions and glacial hydrology. Leonard works on glacier biogeochemistry and cryosphere processes. Silje studies how material released from glaciers affects downstream ecosystems.

Researcher hiking to the next sampling site on Svalbard