Why do we sleep?
Recent research by the University of Rochester, New York shows that a major purpose of sleep is to help the brain cleanse itself of harmful materials.
How does the brain cleanse itself? 
Cerebrospinal fluid (CSF) is a nourishing and cleansing brain fluid. CSF carries essential nutrients into the brain, and transports waste and toxic material out of the brain.
How does CSF flow into and out of the brain?
The brain is comprised of two cell types: “neurons” and “glia.” Glia have a multitude of important tasks and one is to control the flow of CSF. One sort of glial cell is called an “astrocyte” because it looks similar to a radiating star. The tips of some of these star-shaped cells create channels in which CSF flows into and out of the brain. For CSF to actually enter or exit the brain it passes through little holes in the astrocyte tips called “aquaporins.”
What controls the flow of CSF inside the brain?
Astrocytes and other glial cells help control the size of the space through which CSF and other substances flow inside the brain (extracellular space). The extracellular space becomes smaller during wakefulness and larger during sleep. The larger extracellular space allows more CSF to flow inside the brain.
What happens if CSF doesn’t flow well?
When CSF flow is hindered then brain cells can’t receive essential nutrients nor cleanse themselves well. This can cause cell stress that may lead to cell dysfunction. For instance neurodegenerative disorders such as Alzheimer’s and Parkinson’s are associated with a build-up of toxic material in the brain.
Craniosacral Therapy may help CSF flow.
One primary intent of Craniosacral work, a gentle hands-on therapy, is to encourage the flow of CSF. Craniosacral clients often feel like they are falling asleep during treatment. Perhaps this is the body’s way of boosting the effect of craniosacral work by optimizing the size of the space through which CSF flows.
Sleep opens the brain-cleansing pathways.
During sleep the brain’s extracellular space enlarges. This allows more CSF to flow throughout the brain. CSF helps carry essential nutrients to brain cells and helps cleanse the brain of toxic material. This is a very important reason why we need to sleep. Craniosacral work may help enhance this cleansing process during a session when someone is awake. Craniosacral work also helps relax the nervous system so that people sleep better.
The two videos from the University of Rochester below help explain brain cleansing during sleep, and the system that controls CSF flow, called the Glymphatic System.
“Sleep Drives Metabolite Clearance from the Adult Brain”
“The Glymphatic System”