To examine the brain's waste-cleaning process, the research team developed a wireless device that attaches to the forehead. Courtesy of Bundang Seoul National University Hospital

A wireless wearable device has been developed that allows the process by which cerebrospinal fluid washes away waste during sleep to be examined at home. It is expected to make it easy to check whether the brain's cleaning system is operating smoothly, helping to assess the risk of related conditions such as Alzheimer's disease.

On the 9th, a research team led by Professor Chang-ho Yoon of the Department of Neurology at Bundang Seoul National University Hospital and Professor Woon-hong Yeo of the Georgia Institute of Technology in the U.S. announced that they had developed a device capable of continuously observing changes in brain water content during sleep. The results were published in the international journal of convergent science ‘Science Advances’.

During sleep, activity of the ‘glymphatic system’, in which cerebrospinal fluid flows between brain tissues to remove waste such as amyloid beta, becomes more active. Numerous recent studies have reported that if accumulated waste is not cleared efficiently, the risk of neurological disorders, including Alzheimer's disease, increases. The problem is that means of observing the accompanying changes in brain water content are very limited. Magnetic resonance imaging (MRI) can visualize cerebrospinal fluid flow in detail, but because it can be used only inside a scanner room, it has limitations for observing the brain's natural changes during actual sleep.

To address this, the researchers developed a forehead-attached ‘soft wireless near-infrared spectroscopy’ device (a technology that measures changes in tissue water content and blood flow using light absorption) and verified whether stable measurements are possible during sleep. The device arranges LEDs and photodetectors at three wavelengths (640·680·950㎚), and its circuits were designed to be thin and flexible so they conform closely to the forehead. It wirelessly transmits data, enabling continuous measurements even while sleeping at home.

To validate performance, the team conducted a total of 16 overnight at-home measurements in four healthy adults, while simultaneously recording movements used to determine sleep stages, such as electroencephalography and eye movements. Analysis of how signals reflecting changes in brain water content varied across sleep stages showed a pattern in which the brain water signal changed direction each time the sleep stage shifted during the night. When transitioning from wakefulness or REM sleep (a state with heightened brain activity) to non-REM sleep (deep sleep), the signal increased, whereas when transitioning from non-REM sleep to REM sleep, the signal decreased. Because these signal changes occurred almost simultaneously with the moments of sleep-stage transitions, the device was confirmed to capture the brain's actual changes well.

The researchers stated that this is the first case of continuously observing such changes during sleep at home using a wearable device. Professor Chang-ho Yoon said, “Providing a tool to observe glymphatic activity in a natural sleep environment has been a long-standing challenge in research on neurological diseases,” and added, “If this technology advances through comparative validation against standard tests, it could serve as a new observational tool in a wide range of areas, including research on sleep disorders, aging, and cognitive decline.”