Researchers in Korea have developed a technology that can monitor in real-time whether brain waste that causes dementia is being discharged while sleeping.
A joint research team led by Professor Yun Chang-ho from Bundang Seoul National University Hospital's Department of Neurology and Professor Bae Hyun-min from the Korea Advanced Institute of Science and Technology (KAIST) announced on the 23rd that they have developed a non-invasive testing method based on near-infrared spectroscopy capable of observing the activity of the glymphatic system, which is responsible for brain waste discharge during sleep, in real-time, marking a world first. The results of this study were published in the official journal of the International Society for Cerebral Blood Flow and Metabolism, the 'Journal of Cerebral Blood Flow and Metabolism', last month.
When a person falls asleep, cerebrospinal fluid surrounding the brain seeps deeply into the brain along the space around blood vessels to wash away waste, which is discharged through the meningeal lymphatic system or cervical lymph nodes. This system, through which cerebrospinal fluid enters the brain to wash brain tissue and exits, is called the glymphatic system.
A representative waste processed in the brain during sleep is amyloid beta protein, which is cited as a cause of Alzheimer's disease. Amyloid beta protects nerve cells, but when it escapes outside the brain cells and aggregates, it actually destroys the nerve cells.
Until now, there have been limitations in the real-time observation of how the glymphatic system operates during sleep in the human body using non-invasive methods that do not damage brain tissue. Magnetic resonance imaging (MRI) requires the administration of a contrast agent to the cerebral spinal canal, cannot be performed continuously over the 7-8 hours of total sleep time, and it is also difficult to quantify the results.
The research team successfully measured the flow of bodily fluids in the brain in real time using a wireless near-infrared spectrometer sensitive to changes in moisture. The wireless near-infrared spectrometer operates while attached to the forehead, transmitting near-infrared light with wavelengths of 700-1000 nm (nanometers, one billionth of a meter) into the skull, and analyzes the absorption rates of scattered light to calculate brain moisture content, oxygen saturation, blood flow, and more.
In particular, using the 925 nm wavelength sensitive to moisture, the research team explained that an algorithm that removes the effects of brain blood flow (plasma moisture) from the measured moisture content allows precise evaluation of the moisture related directly to glymphatic activity.
In a validation study targeting 41 healthy adults using the device, the research team confirmed that the moisture content in the frontal lobe significantly increased during the transition from waking to non-rapid eye movement (NREM) sleep. As a person sleeps, light sleep (rapid eye movement sleep) and deep sleep (NREM) alternate. This result shows that brain washing activity is activated as they progress into deeper sleep stages, consistent with the glymphatic activation patterns observed in animal experiments.
Professor Yun Chang-ho noted, 'This research is significant in that it establishes a foundation for scientifically elucidating the relationship between sleep and brain health,' and added, 'It could be widely used in early prediction of dementia and other degenerative brain diseases, as well as screening for at-risk groups, and in evaluating the effectiveness of sleep therapy and developing personalized brain health management strategies.'
References
Journal of Cerebral Blood Flow and Metabolism (2025), DOI: https://doi.org/10.1177/0271678X251353142