Glymphatic System

Introduction to the Glymphatic System

The glymphatic system is a network of cavities in the brain that opens up during sleep1, mainly during SWS as a result of neurons shrinking in size2,3. As the neurons shrink, cerebrospinal fluid (CSF) begins to flow through these cavities, to carry metabolic waste products out of the brain or spine into the bloodstream. This behavior is essentially similar to the lymphatic system4. Overall, the clearance rate of amyloid-beta during SWS is twice as fast as being awake5. The brain needs to be mostly shut down to allow these neurons to shrink.

It is important to note that NREM2 doesn’t seem to facilitate the same clearance-boost that SWS does, and the only sleep stage which allows for the enhanced glymphatic activity is SWS.

Most importantly, this process normally takes about 30 to 60 minutes of uninterrupted SWS to complete6. What this means is that the glymphatic system works in cycles of 30-60 minutes long per each clearance session. 

Safety of Different Polyphasic Schedules

Total sleep time Safety Ranking
At least 7.5h
No less than 6h, but less than 7.5h
More than 5h, but less than 6h
At least 4h
At least 3h
No less than 2h, but less than 3h
Less than 2h
  • It is uncertain how effective nap-only schedules can foster this process. This is because naps usually do not provide enough time to fully complete this process.
  • Even though SPAMAYL can have longer naps (~60 minutes), Everyman 4, 5 and Trimaxion have a core sleep of 90 minutes long, these schedules usually borderline on the safety range of glymphatic clearance capacity. Individuals with high SWS requirements and teenagers (who usually need more sleep) will frequently interrupt SWS cycles on these schedules. As a result, SWS disruption will interrupt glymphatic clearance.¬†
  • Do not let total sleep time on a polyphasic schedule fool you! Although a bad idea, but any experimental schedules with no individual sleep sessions longer than ~60m can all pose glymphatic threats!
  • However, the amount of cumulative wastes until the next SWS session on polyphasic sleep is potentially smaller than on monophasic sleep. This may be due to SWS‚Äô occurrence in several naps/core(s) a day.
  • Encountering too many sleep interruptions, or WASOs, can also disrupt SWS!¬†

Therefore, currently there are no absolute conclusions on the health implications of waste products in the brain on nap-only schedules. Regardless, polyphasic schedules with cores should be safe to practice, provided the core has the right placement to maximize SWS gain.

Main author: Crimson & GeneralNguyen

Page last updated: 8 April 2021

Reference

  1. Jessen NA, Munk ASF, Lundgaard I, Nedergaard M. The Glymphatic System: A Beginner’s Guide. N. 2015;40(12):2583-2599. doi:10.1007/s11064-015-1581-6. [PubMed]
  2. Lucey BP, Bateman RJ. Amyloid-ő≤ diurnal pattern: possible role of sleep in Alzheimer‚Äôs disease pathogenesis. N. 2014;35:S29-S34. doi:10.1016/j.neurobiolaging.2014.03.035. [PubMed]
  3. HAMILTON J. Lack Of Deep Sleep May Set The Stage For Alzheimer’s. NPR. https://www.npr.org/sections/health-shots/2016/01/04/460620606/lack-of-deep-sleep-may-set-the-stage-for-alzheimers?t=1539868577354. Published January 4, 2016. Accessed November 4, 2018.
  4. Wostyn P, Van Dam D, Audenaert K, Killer HE, De Deyn PP, De Groot V. A new glaucoma hypothesis: a role of glymphatic system dysfunction. F. 2015;12(1). doi:10.1186/s12987-015-0012-z. [PubMed]
  5. Benveniste H, Liu X, Koundal S, Sanggaard S, Lee H, Wardlaw J. The Glymphatic System and Waste Clearance with Brain Aging: A Review. G. July 2018:1-14. doi:10.1159/000490349. [PubMed]
  6. Xie L, Kang H, Xu Q, et al. Sleep Drives Metabolite Clearance from the Adult Brain. S. 2013;342(6156):373-377. doi:10.1126/science.1241224. [PubMed]