Researchers have developed a flexible patch placed on the forehead during sleep that can detect changes in water dynamics inside the brain, a step that may open the door to studying how the brain clears its metabolic waste during sleep.

The study, published in the journal Science Advances, explained that the patch does not measure cerebrospinal fluid directly, but captures optical signals related to water changes in the brain across different sleep stages.

These changes may be linked to the activity of what is known as the 'glymphatic system,' a pathway within the central nervous system through which cerebrospinal fluid helps remove metabolic waste products and debris from brain tissue.

Brain cleaning

The researchers explained that the activity of this system, considered part of the brain's cleaning mechanisms, is closely linked to sleep, particularly deep sleep stages without rapid eye movement.

They emphasized that better understanding of this process could help explain potential links between sleep disorders and certain neurological diseases, including degenerative diseases associated with protein buildup or cellular debris in the brain.

The new patch relies on near-infrared spectroscopy, a technique that uses light to capture physiological indicators from tissues.

The device contains a photodetector and small lights emitting light at three different wavelengths, allowing it to collect signals related to oxygenated and deoxygenated hemoglobin, as well as water fractions within tissues.

The device uses wavelengths of 640, 680, and 950 nanometers, with a flexible design that enables non-invasive measurement during sleep.

During experiments, the device captured simultaneous data on respiration, heart rate, slow oscillations in brain activity, along with water-related signals.

The researchers said that this ability to collect multiple types of signals simultaneously could make the patch an important research tool for studying sleep in conditions closer to daily life, rather than relying solely on traditional sleep labs or less comfortable devices.

The results showed that brain water dynamics change with transitions between sleep stages; the researchers observed an increase in brain water accumulation when transitioning to non-rapid eye movement sleep, and a decrease when transitioning to rapid eye movement sleep, with these changes paralleling slow-wave activity in EEG.

Biomarker

The researchers believe that these changes could be used in the future as a biomarker to help track sleep stage transitions, and possibly to study sleep disorders or detect early signals related to dysfunction in the brain's cleaning systems.

However, the researchers stressed that the device does not provide a direct measurement of cerebrospinal fluid flow and cannot be considered a diagnostic tool for neurological diseases in its current stage.

Monitoring the glymphatic system in humans is a technical challenge because more direct methods may be complex or unsuitable for continuous recording during natural sleep; thus, a small, soft, non-invasive device could provide a practical means to study this process over hours, with greater comfort for participants.

However, this still requires broader studies to verify the accuracy of the signals captured by the patch, determine their true correlation with glymphatic system activity, and compare them with other measurement methods.

It will also be necessary to test the device on different groups, including people with sleep disorders or neurological diseases, before discussing its clinical use.