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June 2024
Written by: Zoe Hidayat
Edited by: Ramisha Irfan
Over the past years, sleep has been found essential for humans to cleanse toxins and waste materials from our brains. These toxins are flushed out from the small perivascular channels in the glymphatic system, a macroscopic waste clearance system for our central nervous system, the brain. Through this process, it reduced the chances of Alzheimer's and other brain disorders in patients. However, is this Glymphatic theory a myth or fact?
With recent data from Imperial College London, innovative mouse experiments have been used to oppose some perspectives of this decades-old theory. It is done through monitoring the toxin fluids in the brains of mice. By injecting fluorescent dyes into the skull portal of the brains of mice, imperial scientists used a sensor to measure the dye concentration during regular intervals when the mice were asleep and awake. Through this experiment, shocking results were found which contradicted the original findings of the Glymphatic theory. In comparison to the mice awake, scientists discovered that the rate of dye clearing was faster by 30% in sleeping mice and even faster by 50% in mice under anaesthesia.
However, even with solid evidence against the original Glymphatic theory through the increased efficiency of the glymphatic system in the role of toxin clearance in the brain during the awakened state. Many researchers have been scrutinised under constant debate regarding this shocking finding for many valid reasons.
To begin with, the original mice experiments done by neuroscientist Maiken Nedergaard from the University of Rochester included injecting dye into a fluid-filled pocket called cisterna magna and measuring the flow of dye throughout the brain of the mice. Unlike the findings of the imperial researchers, these results supported the idea of the Glymphatic theory. The brain influx increased when mice were under anaesthesia or sleep, concluding that more dye was flowing and draining into the lymphatic vessels caused by the fluid pumping in the tiny glymphatic vessels.
Nevertheless, with much debate, imperial researcher Nicholas Franks raised concerns regarding the experiment done by Nedergaard, noting that the measurement of dye influx into the brains of the mice was near impossible considering the many and various lymphatic exit points and vessels.
Regardless, Nedergaard expressed many concerns regarding the new experiments of the imperial research team. Firstly, the rate of pumping dye in the mice during the intervals of sleep and when the mice were awake might have differed. Moreover, the vital concern of Nedergaard was that inserting the dye into portals into the skull might have damaged certain areas of the brain, causing the fragile glymphatic system to collapse and drastically affecting the accuracy of results. However, researcher Franks still argues that the mice were left a week to heal in case of potential injuries.
Nonetheless, ongoing research is being done by imperial researchers as well as neuroscientist Nedergaard and her team to find the truths regarding the challenge of this generally well-accepted Glymphatic Theory.
References
O’Hare, R. (2024) Scientists find sleep may not clear brain toxins: Imperial News: Imperial College London, Imperial News. Available at: https://www.imperial.ac.uk/news/253273/scientists-find-sleep-clear-brain-toxins/.
Reardon, S. (2024) ‘Does sleep really clean the brain? maybe not, New Paper argues’, AAAS Articles DO Group [Preprint]. doi:10.1126/science.zfoly9p.
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