A Korean research team has developed a wireless wearable device that can continuously observe at home the brain's "cleaning" process of removing waste during sleep.
It is a technology that measures changes in brain water during sleep—previously confirmable only by magnetic resonance imaging (MRI)—with a near-infrared spectroscopy (NIRS) device attached to the forehead. With further validation and development, it is expected to become a new tool for research into neurological disorders such as dementia and sleep disorders.
The research team led by Neurology Professor Yun Chang-ho at Bundang Seoul National University Hospital (co-corresponding author Yeo Woon-hong at Georgia Institute of Technology) said on the 9th that it had developed a wireless wearable device that can continuously observe at home changes in water inside the brain related to the brain's recovery and housekeeping processes during sleep.
The study, conducted jointly with Georgia Institute of Technology Professor Yeo Woon-hong, was published in Science Advances, a leading international journal in convergent science.
While sleeping, the brain actively carries out a cleaning process that washes away waste accumulated during the day.
This cleaning system, called the glymphatic system, removes waste such as amyloid-beta as cerebrospinal fluid flows between brain tissues, and it is known to become particularly active during deep sleep stages.
As studies have found that when this process does not function smoothly, the risk of neurological diseases, including Alzheimer's dementia, increases, the brain's cleaning process during sleep has recently drawn attention in brain health research.
The problem is that means to observe brain water changes related to this cleaning process have been very limited. MRI can visualize cerebrospinal fluid flow in detail, but because it is equipment usable only inside the exam room, it had limits in repeatedly observing actual changes during sleep.
In response, the team developed a soft, wireless near-infrared spectroscopy (NIRS, a technique that measures changes in water and blood flow in tissue using light absorption) wearable device that can be attached to the forehead.
The device is equipped with LEDs and photodetectors at three wavelengths (640 nm, 680 nm, 950 nm). It transmits data wirelessly, allowing continuous measurement even while sleeping at home. The thin, flexible circuitry adheres to the forehead without discomfort, enabling stable, overnight measurement of brain water changes during sleep without disturbing sleep.
The design that gently conforms to the skin was handled by the research team of Georgia Institute of Technology Professor Yeo Woon-hong, an authority in soft electronics.
To validate the device's performance, the team conducted a total of 16 overnight measurements at home in four healthy adults. At the same time, they determined sleep stages based on electroencephalography and electrooculography, then analyzed how signals indicating changes in water content within brain tissue varied at each stage.
As a result, a patterned, directional change in brain water signals was observed each time sleep stages shifted through the night.
Signals increased when transitioning from wakefulness or REM sleep (REM, a stage with heightened brain activity) to NREM sleep (NREM, deep sleep). Conversely, they decreased when transitioning from NREM to REM sleep. Notably, these signal changes occurred almost simultaneously with the timing of sleep stage transitions determined by electroencephalography and electrooculography, confirming that the wearable device can accurately capture actual changes inside the brain.
The signals captured by the device reflected not only brain water changes but also physiological rhythms associated with breathing, heartbeat, and slow brain waves. The team said that in NREM sleep, breathing and heart rate remained stable, while in REM sleep they became more irregular, mirroring well-known physiological patterns during sleep.
According to the research team, this is the first case of continuously observing these sleep-related changes at home with a wearable device.
Professor Yun Chang-ho said, "Providing a tool to observe glymphatic activity in a natural sleep environment has long been a task in neurological disease research," and added, "With support from the National Research Foundation of Korea (NRF), we are conducting follow-up studies to build datasets in healthy people and patients with cognitive impairment, refine glymphatic-related indices, and evaluate various intervention effects such as sleep apnea treatment and cognitive behavioral therapy for insomnia."
Yun added, "If this technology advances through comparative validation against standard tests, it could be used as a new observational tool in various areas, including research on sleep disorders, aging, and cognitive decline."
References
Science Advances (2026), DOI: https://doi.org/10.1126/sciadv.aed2056