While You Sleep, Your Brain Cleans Itself: The Role of the Glymphatic System by Reginald Deschepper
We all know that sleep is important for our concentration, memory, and mood. But over the past decade, neuroscientists have discovered something remarkable: during deep sleep, your brain is literally rinsed clean. Waste products that accumulate throughout the day are flushed out at night through a specialized cleansing system—the glymphatic system. This discovery is changing the way we think about sleep, brain aging, and dementia.
What Is the Glymphatic System?
For a long time, scientists believed that the brain had no lymphatic system to remove waste. That turned out to be wrong. In 2012, researchers discovered a unique network of channels surrounding the blood vessels in the brain, allowing cerebrospinal fluid to flow through brain tissue. Glial cells—the brain’s support cells—play a key role in this process, which is why it was named the glymphatic system. You can think of it as the brain’s nightly cleaning crew.
During deep, slow-wave sleep, something remarkable happens:
- brain cells shrink slightly, increasing the space between them
- the flow of cerebrospinal fluid becomes up to 60% more efficient
- waste products such as amyloid-beta and tau are cleared more effectively
These very proteins play a central role in the development of Alzheimer’s disease. That makes deep sleep a crucial protective factor for your brain.
One bad night is not a problem. But years of insufficient deep sleep can lead to slower clearance of waste products, more inflammation, and potentially a higher vulnerability to cognitive decline.
What Changes With Age?
As we grow older, sleep becomes lighter and more fragmented. The amount of deep sleep gradually decreases, and the glymphatic system becomes less efficient as well. This does not mean dementia is inevitable, but it does show that sleep becomes increasingly important as a maintenance period for the brain.
Practical Tips
- Consistency is crucial: go to bed and wake up at regular times
- Limit bright light and screen use during the last hour before sleep
- Avoid alcohol, especially late in the evening (it suppresses deep sleep)
- Stay physically active during the day, but avoid intense exercise right before bed
- Keep your bedroom cool and dark
- Do you snore or stop breathing at night? Consult your doctor to check for sleep apnea
Can You Track “Brain Cleaning” With a Sleep Tracker?
Although we can’t directly measure the glymphatic system with a ring or smartwatch, we can monitor deep sleep—which is closely linked to nightly brain cleansing.
Trackers such as the Oura Ring, Apple Watch, Garmin, or Fitbit estimate deep sleep using micro-movements, heart rate, and heart rate variability. This is not a direct brain measurement, but it is a reliable way to track trends. If you notice, for example, that you are getting almost no deep sleep for weeks, that could indicate suboptimal recovery.
The big advantage is that these measurements are accessible, affordable, and suitable for long-term use. Still, they provide an estimate—not a medical diagnosis.
Another important consideration: tracking sleep can sometimes cause unintended stress. Some people start worrying about their scores, feel performance pressure (“I must sleep well”), or become more restless at night.
In a striking sham-EEG study, participants were told they had slept well or poorly—completely unrelated to their actual sleep quality. Those who believed they had slept poorly performed worse on cognitive tests (memory, concentration, mental flexibility), purely because of their perception.
Use sleep tracking as a compass, not an exam. And remember: a single bad night is not a disaster, especially if you keep it in perspective.
Sources
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Fultz, N. E., et al. (2019). Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleep. Science, 366(6465), 628–631.
https://doi.org/10.1126/science.aax5440
Rasmussen, M. K., Mestre, H., & Nedergaard, M. (2018). The glymphatic pathway in neurological disorders. The Lancet Neurology, 17(11), 1016–1024. https://pubmed.ncbi.nlm.nih.gov/30353860/
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