Sleep, quite literally, makes our brains healthier. And why is this so?

The simple answer is that a good night's sleep helps your body remove the toxins that accumulate during your waking hours from all that physical and mental effort. It's like your brain dumps the toxic trash you put into your body during the daylight hours.

But the more complex answer explains how our brains achieve this miracle of regeneration every night. This nightly cleansing process involves two types of cells — microglial cells and astrocytes — which always perform this cleaning process.

Located throughout the brain and spinal cord, microglial cells or microglia are the first and main form of active immune defense in our central nervous system (CNS). Microglia are key cells in overall brain maintenance.

They relentlessly scavenge the CNS for plaques, damaged or unnecessary neurons and synapses and a host of infectious agents. They do their best work when we sleep.

They also play a role in keeping Alzheimer's disease at bay. Microglia help remove beta-amyloid, a toxic protein commonly found in the brains of Alzheimer’s disease patients.

On the other hand, astrocytes are star-shaped glial cells in the brain and spinal cord that perform many functions. These include pruning unnecessary synapses, repairing the brain’s neural wiring, biochemical support of endothelial cells that form the blood-brain barrier (BBB) and the provision of nutrients to the nervous tissue. Equally important, astrocytes play a key role in the repair and scarring process of the brain and spinal cord following traumatic injuries.

But microglial cells and astrocytes have a dangerous "Jekyll and Hyde" personality. They function at their best while we sleep. If we don't get enough sleep, they'll instead attack healthy, functioning tissues, causing damage to our brain and bodies.

“We know sleep is really important for brain health, and waste clearance is probably a key reason why; what was less clear is: Why is this changed during sleep?” asked neuroscientist Laura Lewis of Boston University. “That led us to ask what was happening in the CSF.”

Lewis led a team that sought to find the answer to this question. The research team monitored the brain waves of 13 healthy adults while they slept.

They used electroencephalography (EEG) and an advanced fMRI (functional magnetic resonance imaging) technique that was able to capture changes at a faster rate than a standard fMRI. They found that in non-REM (rapid eye movement) sleep, the slow waves occurred simultaneously with changes in blood flow and CSF (cerebrospinal fluid). This made researchers conclude that as brain activity causes changes in blood flow, the volume of blood in the brain is reduced, and CSF then flows in to fill up the space.

“We’ve discovered there are really large waves of CSF that appear in the brain only during sleep,” Lewis added. “This effect is really striking, and we’re also interested in what it means for maintaining brain health, especially in disorders such as Alzheimer’s disease.”

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Sleep deprivation has been linked to health problems, including obesity, diabetes, high blood pressure and heart disease. Pixabay