How Does Our Brain Get Rid Of Toxins?

Oct 21, 2016
Originally published on November 4, 2016 8:08 am

Part 4 of the TED Radio Hour episode Toxic

About Jeff Iliff's TED Talk

Neuroscientist Jeff Iliff talks about his research, which explores how the brain naturally flushes out toxins during sleep.

About Jeff Iliff

Neuroscientist Jeff Iliff is an Assistant Professor of Anesthesiology and Perioperative Medicine at Oregon Health & Science University. Iliff was a part of a University of Rochester Medical Center team that discovered a brain cleansing system, which they dubbed the "glymphatic system."

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On today's show, we're talking about things that are toxic. And so far, we've heard about toxins like pollution and industrial chemicals. But for scientists like Jeff Iliff...

JEFF ILIFF: I'm an assistant professor at Oregon Health & Science University.

RAZ: A toxin can be something in the cells of your own body.

ILIFF: Yeah, so cells are like little engines, you know, they burn sugar and they use up oxygen. And in the process they produce all kinds of waste.

RAZ: Like carbon dioxide, which is toxic in certain amounts. And that's not all.

ILIFF: You know, ammonia is a molecule that your cells produce.

RAZ: Ammonia, like, you know, the stuff in glass cleaner is also a chemical byproduct of your metabolism.

ILIFF: Yeah. There's simple molecules like that. But then there's even more damaging, more complex molecules like certain proteins that can be produced that can have toxic effects if they build up to high enough levels.

RAZ: And, yeah, every cell in your body produces these toxins. But the good news is we have organs to process and get rid of them. But there's one place in your body where toxins are much, much more dangerous...

ILIFF: Your brain.

RAZ: Your brain has its own way of dealing with toxins.

ILIFF: So it has something called the blood-brain barrier, which is this - it's like a castle wall that walls the brain and the spinal cord in, and walls everything else from the rest of your body out. And so that sealing of the brain behind this barrier creates this other problem of, well, how do you deal with toxins that are made inside the castle?

RAZ: Because remember, every cell in the body produces a tiny amount of toxic waste, even in the cells inside your brain. So how do we get rid of that? Here's Jeff on the TED stage.


ILIFF: Two-thousand years ago, Galen - one of the most prominent medical researchers of the ancient world - proposed that while we're awake, our brain's motive force - its juice - would flow out to all the other parts of the body, animating them but leaving the brain all dried up. And he thought that when we sleep, all this moisture that filled the rest of the body would come rushing back, rehydrating the brain and refreshing the mind. Now that sounds completely ridiculous to us now. But Galen was simply trying to explain something about sleep that we all deal with every day.

So we all know based on our own experience that when you sleep, it clears your mind. And when you don't sleep, it leaves your mind murky. But while we know a great deal more about sleep now than when Galen was around, we still haven't understood why it is that sleep - of all of our activities - has this incredible restorative function for the mind. I want to tell you about some recent research that may shed new light on this question. We've found that sleep may actually be a kind of elegant design solution to some of the brain's most basic needs.

RAZ: And one of those needs - flushing out toxins.

ILIFF: So you can think of the brain sort of as almost like a, you know, a big sponge, right?

RAZ: But the sponge acts differently depending on whether you're awake or asleep.

ILIFF: What appears to happen is when you're awake if you were to, say, run water over that sponge - it's like if you had a very dense sponge that had very small gaps that ran through it - and very little of the water would actually wash through the sponge.

RAZ: And that's because when you're awake, your brain cells seem to be packed tightly together. There's not a lot of space between them.

ILIFF: But if that sponge suddenly underwent a change where all the gaps in between suddenly opened up, all of a sudden fluid is relatively free to move through.

RAZ: And your brain - it has exactly the fluid to do that. It's called CSF, or cerebral spinal fluid.

ILIFF: CSF is this really incredible clear fluid that is almost completely protein-free. So it's like this very clean salt water almost. So what the brain actually does is it floats in this sea of salt water, you know, like a person floating in a swimming pool where you feel more-or-less weightless...

RAZ: Yeah.

ILIFF: ...The brain is in much the same way.

RAZ: So during the day, your brain is happily floating in CSF. But when we sleep - and this is according to a study by Jeff and his team of researchers - CSF washes into the brain. And it flushes out toxins that our brain cells produce all day long.

ILIFF: That appears to be at least one of the ways that the body manages waste that it needs to get rid of on a daily basis.


ILIFF: The waste product that these recent studies focus most on is amyloid beta, which is a protein that's made in the brain all the time. My brain's making amyloid beta right now and so is yours. But in patients with Alzheimer's disease, amyloid beta builds up and aggregates in the spaces between the brain cells instead of being cleared away like it's supposed to be. And it's this buildup of amyloid beta that's thought to be one of the key steps in the development of that terrible disease.

A series of recent clinical studies suggest that among patients who haven't yet developed Alzheimer's disease, worsening sleep quality and sleep duration are associated with a greater amount of amyloid beta building up in the brain. And while it's important to point out that these studies don't prove that lack of sleep or poor sleep cause Alzheimer's disease, they do suggest that the failure of the brain to keep its house clean by clearing away waste like amyloid beta may contribute to the development of conditions like Alzheimer's.

RAZ: Is it possible that there are other functions helped by sleep that we, you know, that we haven't yet discovered?

ILIFF: I think it's not only possible, I think it's very likely. One might be immune surveillance of the brain. So how does the rest of the body detect whether there's an infection in the brain or not? Is that something that's happening during sleep? Impairment in sleep, especially chronic sleep disruption, is associated with all kinds of health conditions that you don't necessarily think of as being driven by the brain.

What those connections are and why they're connected isn't necessarily clear. But there's probably other things that are happening during sleep that we haven't even sort of conceived of yet that we're going to discover in the next five, 10, 15 years.

RAZ: That's Jeff Iliff. He's a neuroscientist at Oregon Health & Science University. You can watch his entire talk at

More ideas about toxins in just a moment. I'm Guy Raz and you're listening to the TED Radio Hour from NPR. Transcript provided by NPR, Copyright NPR.