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
• 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. ¹⁾
  • it relies on vasomotion (rhythmic constriction and dilation of blood vessels) to drive CSF through the interstitial space and clear waste from the brain²⁾
  • two main flow processes³⁾:
    • 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 ⁴⁾
• it has been proposed that glymphatic dysfunction is the central cause of delirium⁵⁾
• 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 sleep⁶⁾