CSF: Too Much Can Kill You, But You Need it to Stay Alive

Those of us who are afflicted with--or have family members who are afflicted with---hydrocephalus may wonder why the brain produces so much cerebrospinal fluid (as much as three cups per day) when the body's capacity to store CSF is at most half that amount. If something goes wrong with the CSF drainage system, swelling, brain damage, and death can occur within hours. (The usual treatment is the installation of a plastic shunt that diverts the CSF to the abdomen where it can be absorbed easily; however, shunts must be monitored continually for blockages.)

But back to the original question: why manufacture so much CSF? The answer may be that chemical changes in the cerebrospinal fluid cause us both to fall asleep and to awaken. CSF's chemical composition varies throughout the 24-hour cycle; also, the volume must be sufficient to flush away the brain's waste products [bold added]

by altering the concentrations of potassium, calcium, magnesium, and proton ions found in the fluid, the researchers observed that they could manipulate the sleep-wake state of mice in the absence of neurotransmitters. Potassium in particular appears to play a key role as the levels of the ion fluctuate rapidly during sleep-wake transitions.

because the ions are positively charged, as they move back and forth between CSF and brain cells, they can change the electrical activity of cells, causing them to either polarize or depolarize. When depolarization occurs in neurons, the cells become excitable, alert, and awake.

The findings may reveal how the brain is able to accomplish the task of activating billions of nerve cells quickly, simultaneously, and on a global scale when we transition from sleep to awake. It may also show how the brain is able to maintain a state of sleep or wakefulness over an extended period of time by altering the electrical potential of nerve cells.

The researchers also observed that the chemical changes impacted the volume of brain cells. Specifically, they found that nerve and support cells in the brain shrink while we sleep, creating more space for cerebral spinal fluid to flush away waste.

CSF: too much can kill you, but you need it for sleep...and life itself.