Grow Youthful: How to Slow Your Aging and Enjoy Extraordinary Health
Grow Youthful: How to Slow Your Aging and Enjoy Extraordinary Health

Why sleep is essential for your brain

Sleep is for detoxification

How a mammal's brain detoxifies

References

Sleep is for detoxification

For years I have written in Grow Youthful that the primary reason we need sleep is for detoxification. All animals need to sleep. If you don't get enough sleep you feel dreadful, and your body responds to the build-up of toxins in a variety of ways, both short-term and long-term. Experiments have shown that a total lack of sleep for long periods can even kill.

Until recently there was little research to show why animals incur the huge cost of spending around a third of their lives sleeping. Maiken Nedergaard University of the Rochester Medical Center has now shown that sleep is the primary mechanism for the removal of toxic metabolic waste generated by the brain.

The lymphatic system collects and disposes of cellular waste around the body, but it does not include the brain or spinal cord. This is because the brain is protected by the blood-brain barrier, a membrane-like gateway that tightly controls what enters and exits the brain. The brain must have a waste-removal system, because the accumulation of toxic cellular waste proteins such as amyloid-beta can lead to neurodegenerative diseases such as Alzheimer's disease.

How a mammal's brain detoxifies

How the brain manages to dispose of its waste has long eluded scientists. Until now they were not able to observe the process in a live brain, but new imaging technologies (two-photon microscopy) have let them observe a previously undiscovered plumbing system in the brains of mice. Mice brains are similar to those of humans in many ways. This plumbing system piggybacks on the brain's blood vessels and pumps cerebral spinal fluid (CSF) through brain tissue, flushing out wastes back into this circulatory system and then into the general blood circulation system.

This brain waste disposal system has been dubbed the glymphatic system. Another clue that tipped the researchers that an important process is going on while we sleep is that the amount of energy consumed by the brain does not decrease much when we sleep. Pumping CSF uses a lot of energy, and this detox system cannot operate when we are awake and actively processing information.

One of the most interesting findings was that the cells in the brain "shrink" by 60% during sleep. This creates more space between the cells so the CSF can wash through the brain tissue. In contrast, when awake the brain's cells are so close together that the glymphatic system cannot work.

Noradrenaline is a fight-or-flight hormone that is released in bursts when brain needs to become alert. The researchers observed that this neurotransmitter is less active in sleep, and speculate that noradrenaline may serve as a "master regulator" controlling the contraction and expansion of the brain's cells during the sleep-wake cycle.

"These findings have significant implications for treating 'dirty brain' disease like Alzheimer's," said Nedergaard. "Understanding precisely how and when the brain activates the glymphatic system and clears waste is a critical first step in efforts to potentially modulate this system and make it work more efficiently."

References

1. Jeffrey J. Iliff, Hedok Lee, Mei Yu, Tian Feng, Jean Logan, Maiken Nedergaard, Helene Benveniste. Brain-wide pathway for waste clearance captured by contrast-enhanced MRI. J Clin Invest. 2013 March 1; 123(3): 1299-1309. Published online 2013 February 22. doi: 10.1172/JCI67677. PMCID: PMC3582150.

2. Jeffrey J. Iliff et al. A Paravascular Pathway Facilitates CSF Flow Through the Brain Parenchyma and the Clearance of Interstitial Solutes, Including Amyloid B. Sci Transl Med 4, 147ra111 (2012). DOI: 10.1126/scitranslmed.3003748.

3. Maiken Nedergaard, Lulu Xie, Hongyi Kang, Qiwu Xu, Michael Chen, Yonghong Liao, Thiyagarajan Meenakshisundaram, John O'Donnell, Daniel Christensen, Takahiro Takano, Rashid Deane, Jeffrey Iliff, Charles Nicholson. Sleep Drives Metabolite Clearance from the Adult Brain. Science, 18 October 2013: Vol. 342 no. 6156 pp. 373-377. DOI: 10.1126/science.1241224.