Maiken Nedergaard

Sleep is still one of the biggest mysteries in biology, and we still do not know why it is so important to sleep.

I think we all feel on our body on a daily level how much sleep actually matters for our performance and our well-being the following day.

We now realize that sleep is so much more than that, and that probably many both immune action, many housekeeping function that's going on in sleep, and it's not all about memory performance.

All other organ and tissue can do the housekeeping, the cleaning when we are asleep, when we are awake at any time point.

The brain appears to only be able to do the basic housekeeping when we are asleep.

Yeah, what we found in a nutshell was that if we injected colored substances in the cerebrospinal fluid that surround the brain, we found that if the animal was asleep, they were pumped straight back into the brain.

And this was a very unexpected finding because the cerebrospinal fluid is supposed to be basically produced by the brain and then protect the brain and leave the brain.

And then when we started to do awake mice, we saw, wow, it doesn't happen.

So, of course, we mistrusted it.

We repeated it many times, used different techniques, and we published it.

Yes, so that is a big deal.

So all the basic concept of the glymphatic system was defined in mice and rats.

But very quickly, just a few years later, people start to replicate this finding and could confirm the core principle of the glymphatic system.

For example, that it turns on when we sleep, it turns off when we awake, and it follows a certain pattern or organization of fluid flow.

Yeah, there has been about 3,000 papers published on the glymphatic system.

And what people have done so far is to describe the drivers of it, that it is significantly reduced activity.

in all neurodegenerative diseases.

So this is Alzheimer, Parkinson, frontotemporal dementia, and so on.

It's decreased, and aging in itself would decrease it.

It's also been shown that it's suppressed by wakefulness, and if you keep awake for just one night, it takes at least two days or more to clean out the waste that accumulated during that night.