We all know we need it and we know we don’t function well without it but neuroscientists have only recently discovered why it’s so important for human beings to sleep. It’s our brain. That is, we now know that at least one of the reasons sleep is important is because without it, our brains would cease to function properly.
So why is it that we’re groggy and irritable if we don’t get a good night’s sleep? Neuroscientists have discovered that when we don’t sleep, the toxic waste build up in our brains increases. When we sleep, it decreases.
Every cell in the human body produces waste as a byproduct. But more importantly every cell has a waste disposal system. When waste builds up, it becomes toxic. Our lymphatic system acts somewhat like our household plumbing, taking all of the waste and getting rid of it. It’s a sophisticated network of vessels, which collects protein and waste from the spaces between our cells. It then transfers it into the blood for it to be disposed of.
But the brain isn’t like a regular organ or other cells in the body. Up until now, we didn’t know how the brain disposed of its toxic waste. Sure it has a rich supply of blood vessels, bringing freshly, oxygenated blood and nutrients to the brain cells, but until recently, it was believed that there is no lymphatic system in the brain. So how does the brain remove waste?
Neuroscientist Jeff Iliff, who explores the unique functions of the brain, has been researching that very question. They knew that the cerebrospinal fluid (CSF) that cushions the brain from the skull was the main waste disposal pool for the brain. But they had no idea how the waste travelled from the brain cells to the CSF surrounding the brain.
Performing MRIs on the brain they noticed that during the day, when a person was awake, the CSF, appearing as a bright green liquid, encased the brain. Almost no CSF was found inside the brain, save a few green dots penetrating the outer layer.
However at night, when the person was asleep, it was a different story. Something quite remarkable happened. As the night progressed, the green dots of cerebrospinal fluid started to increase inside the brain. As sleep continued the dots increased in number until they became an indistinguishable haze of green, flooding the brain. The CSF had moved into the brain, like a green mist, bathing each and every cell in the brain.
Iliff noticed the CSF was using the capillaries that brought the blood supply to the brain, to access the brain tissue. Instead of the CSF traveling inside the capillary, it was running down the outside of the capillary. Much like rain runs down the outside of downpipe, the CSF was using the outside structure of the capillary to make its way between the cells in the brain.
Moreover, the MRI showed the brain cells themselves had shrunk, in order to increase the space between the cells. This gave the CSF more surface area to cover.
The CSF, having collected the cellular waste then returns it to the main pool of CSF surrounding the brain, which then dumps the toxic waste back into the blood.
So what happens if you don’t sleep? Or you don’t sleep enough?
Firstly, the amount of CSF rushing into our brain is significantly reduced. This means that toxic waste isn’t clearing from our brain. Brain cells produce a protein called amyloid-beta. Neuroscientists have measured how much of this protein is cleared from the brain when it is asleep compared to when it’s awake. The difference is startling, the clearance of amyloid-beta is much more rapid in the sleeping brain. Alzheimer’s patients have an accumulation of amyloid-beta that builds up and aggregates in the spaces between the brain cells. This build up of amyloid-beta is what is thought to be one of the key elements in the development of Alzheimer’s disease.
As Iliff quotes,
“Like our housework, it’s a dirty and a thankless job, but it’s also important. In your house, if you stop cleaning your kitchen for a month, your home will become completely unlivable very quickly. But in the brain, the consequences of falling behind may be much greater than the embarrassment of dirty countertops, because when it comes to cleaning the brain, it is the very health and function of the mind and the body that’s at stake.”
Sustained sleep deprivation makes it hard to think, everything gets jumbled up. Concentration is poor, co-ordination is poor, memory is poor. If we don’t sleep, we don’t get rid of the build up of toxic waste, and even simple tasks can become overwhelming. It’s like trying to make a cup of tea in a kitchen over run with dirty dishes, piled up on countertops. Almost impossible.
It’s precisely why after a good nights sleep we feel more alert, emotionally stable and clear headed. We’ve essentially done a load of dishes, wiped down the counter and mopped the floor. Everything is cleaner and it’s far easier to make that cup of tea.