see also:

• the brain

• discovered in 2012, the glymphatic system is a “pseudo-lymphatic” perivascular network distributed throughout the brain, responsible for replenishing as well as cleansing the brain.
• glymphatic clearance is the macroscopic process of convective fluid transport in which harmful interstitial metabolic waste products are removed from the brain intima
• in 2019, Lewis reported a way to use functional magnetic resonance imaging (fMRI) to measure CSF waves as they flow in and out of the brain during sleep and showed that these waves are tightly coupled with EEG brain waves called slow waves, which are associated with deep sleep, and these stimulate blood vessels to constrict and dilate, allowing them to act as a pump that drives CSF out of the brain. In 2026, she showed that synchronised 50msec microbursts of pink noise (similar to steady rain or a distant waterfall) can increase CSF flows.¹⁾
• sleep is a primary driver of glymphatic clearance
  • there appears to be a 90% reduction in glymphatic clearance during wakefulness, and twice the amount of protein clearance from the brain intima during sleep - and it appears that the majority of glymphatic clearance activity occurs during N3 sleep which occurs in non-REM deep sleep and glymphatic transport is most efficient in the right lateral sleeping position, with more CSF clearance occurring compared to supine and prone. ²⁾
  • it relies on vasomotion (rhythmic constriction and dilation of blood vessels) to drive CSF through the interstitial space and clear waste from the brain³⁾
  • two main flow processes⁴⁾:
    • fast flow:
      • fluid moves at a few microns per second around the brain's open regions such as the surface between the skull and the brain
    • slower flow:
      • fluid trickles through the brain's deep tissue at a rate about 50 times slower
• it appears to reduce in efficiency as we age
• low doses of alcohol (0.5 g/kg) appears to increase glymphatic clearance but higher levels reduce it
• glymphatic clearance can be manipulated by sleep deprivation, cisterna magna puncture, acetazolamide or genetic deletion of AQP4 channels
• intermittent hypercapnia, exposure to low levels of CO2 in ON-OFF cycles, elicited vasomotion-induced cerebrospinal fluid inflow in both healthy controls and individuals with Parkinson’s disease
  • a 2025 study showed that intermittent hypercapnia, administered in three 10-minute sessions totaling approximately 30 minutes, increased the appearance of total α-synuclein, neurofilament light, glial fibrillary acidic protein, amyloid β1-42, amyloid β1-40, and phosphorylated tau 217 in the plasma of both healthy controls and individuals with Parkinson’s disease suggesting it can help clear potentially toxic brain byproducts from the brain ⁵⁾
• it has been proposed that glymphatic dysfunction is the central cause of delirium⁶⁾
• variants of the aquaporin‑4 (AQP4) gene, which helps regulate the glymphatic system may increase risk of Alzheimer's disease - those carrying certain AQP4 variants showed faster grey matter loss when they reported shorter sleep⁷⁾