Summary: Researchers have developed a wearable, noninvasive device that continuously monitors the brain’s glymphatic system — the clearance network that removes waste and supplies nutrients to brain tissue — across sleep stages. Previously measurable only with MRI, this new head-cap with embedded electrodes records fluid shifts, neural activity, and vascular changes to track glymphatic function through the night.
The study shows that glymphatic activity does not operate as a simple on/off switch between sleep and wake. Instead, clearance steadily increases during sleep and tapers off gradually upon waking. These results deepen understanding of how sleep quality and sleep stage transitions affect brain health and may help identify people at higher risk for neurodegenerative diseases such as Alzheimer’s.
Key findings:
- Continuous monitoring: A wearable head cap uses electrical impedance and embedded electrodes to measure glymphatic flow continuously through sleep, eliminating the need for MRI for routine, time-resolved assessment.
- Glymphatic dynamics: Increased waste clearance was observed not only during slow-wave sleep but also during deep and REM sleep and during the transition to wakefulness; glymphatic function accelerates with prolonged sleep and declines gradually after waking.
- Clinical potential: This monitoring approach could enable earlier detection of glymphatic dysfunction, support development of therapies that target brain clearance, and help evaluate treatments aimed at preventing or slowing neurodegenerative disease.
Source: University of Washington
Study overview
A team led by researchers at the University of Washington evaluated a wireless, multimodal wearable developed by Applied Cognition that records sleep-related changes in brain tissue impedance, cortical electrical activity (EEG), and cardiovascular signals. Participants wore the electrode-embedded head cap while sleeping, allowing continuous assessment of fluid movement through the brain parenchyma and its association with sleep state.
By combining impedance spectroscopy with EEG and vascular measurements, the investigators were able to infer changes in extracellular fluid volume that reflect glymphatic activity. This approach enables time-resolved tracking of brain clearance across multiple sleep stages in naturalistic settings — something that conventional MRI cannot do because of limited temporal resolution and the impracticality of long overnight scans.
In contrast to the prevailing notion — largely derived from animal studies — that glymphatic clearance is active only during sleep and predominately during slow-wave sleep, the human data revealed a more nuanced pattern. Glymphatic function increased across deep sleep and REM, and it remained engaged during awakening, with the greatest clearance seen as sleep progressed and a gradual decline after waking.
“We have long assumed glymphatic function behaved like a binary switch: on during sleep, especially slow-wave sleep, and off while awake,” said Jeffrey Iliff, coauthor of the study and a professor of psychiatry and neurology at the University of Washington School of Medicine. The human recordings challenged that model, showing progressive changes rather than abrupt state-dependent shifts.
Understanding these dynamics is important because the glymphatic system helps remove proteins and metabolic waste whose accumulation is linked to neurodegenerative disorders such as Alzheimer’s and Parkinson’s. Continuous monitoring of glymphatic function could therefore be a crucial tool in both research and clinical care, helping to identify individuals at risk, measure disease progression, and evaluate treatments designed to enhance brain clearance.
The wearable platform could be applied in several ways: to determine whether impaired glymphatic clearance contributes to Alzheimer’s, traumatic brain injury, migraine, and other neurological conditions; to support development and testing of drugs or interventions that improve glymphatic flow; and to identify patients most likely to benefit from such therapies.
This clinical validation work involved participants at the University of Washington Medical Center – Montlake and the University of Florida between October 2022 and June 2023. The study included 35 participants in a benchmarking cohort in Florida and 14 participants in a replication cohort in Seattle, with ages ranging from 56 to 66 years.
Swati Rane Levendovszky, an MRI physicist and former director at UW Medicine’s Diagnostic Imaging Sciences Center who now works at the University of Kansas Medical Center, contributed to the project. Applied Cognition’s CEO, Dr. Paul Dagum, emphasized the study’s translational potential for identifying therapeutics that improve glymphatic clearance.
Funding and disclosures: The study was funded by Applied Cognition. Jeffrey Iliff served as chair of the company’s scientific advisory board and received compensation in that role.
About this neurotech and neuroscience research
Author: Barbara Clements
Source: Washington University
Contact: Barbara Clements – Washington University
Image: Image credit: Neuroscience News
Original research (open access): “A wireless device for continuous measurement of brain parenchymal resistance tracks glymphatic function in humans” by Jeffrey Iliff et al., Nature Biomedical Engineering.
Abstract (summary)
Glymphatic function in animal models supports the clearance of brain proteins whose mis-aggregation is implicated in neurodegenerative diseases such as Alzheimer’s and Parkinson’s. Measuring glymphatic function in humans has been difficult because existing methods are invasive or lack the temporal resolution needed to follow sleep-related changes.
This report describes a noninvasive, multimodal wearable device that continuously measures sleep-associated changes in brain parenchymal resistance using repeated electrical impedance spectroscopy. Two clinical validation studies show the device’s measurements track sleep-related changes in extracellular volume that regulate glymphatic function and predict glymphatic solute exchange assessed by contrast-enhanced MRI.
The device replicates preclinical observations linking increased glymphatic function with higher sleep EEG delta power and decreased function with higher EEG beta power and elevated heart rate. By enabling continuous, time-resolved assessment of parenchymal resistance in natural settings, this investigational platform provides a tool to determine whether glymphatic impairment contributes to Alzheimer’s disease risk and progression and to support studies that modulate glymphatic function in humans.