Sleep-Deprived Rats Take 'Brain Naps'

Reporting in the journal Nature, researchers measuring brain activity in sleep deprived-rats say some neurons in rats' brains can enter a sleep state, even though the rats are still awake. UCLA Medical School psychiatry professor Christopher Colwell explains the findings.

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This is SCIENCE FRIDAY. I'm Ira Flatow.

Can your brain take mini-naps, even while you're awake? Scientists report in the journal Nature this week that they've seen rat brains do just that. The rats were sleep-deprived, hooked up to EEG machines, those brainwave machines, so the researchers could monitor their brain activity.

And in this awake-but-sleepy state, they found that some cells in the rats' brains could actually go offline, as they called it, and switch to a sleep state. And this happened even though the rat was moving around and performing different tasks with no signs of overt sleepiness.

But when they were tested, the rats scored worse on tests of their motor skills. This kind of sleep-deprived but functioning, sound familiar? I'll bet it does. The question then is: Can this research tell us anything about humans, especially those working in a sleep-deprived state?

That's what we'll be talking about first up this hour. Our number, 1-800-989-8255. You can tweet us, @scifri, @-S-C-I-F-R-I. Or go to our Facebook page or our website.

Let me introduce my guest. Christopher Colwell is a neuroscientist and a professor in the Department of Psychiatry at the University of California Los Angeles Medical School. Welcome to SCIENCE FRIDAY, Dr. Colwell.

Dr. CHRISTOPHER COLWELL (Professor, Department of Psychiatry, University of California Los Angeles Medical School): Thanks, glad to be here.

FLATOW: So you found that when you hook these rats up to the brainwave machines, you found that even though the rat was awake, some of the neurons, the cells in the brain, were sleeping actually. You didn't do that. You were just commenting on that brain study in the journal

Dr. COLWELL: Exactly. So - yeah, to be clear, this is Professor Tonini's(ph) work from the University of Wisconsin. But I'm intrigued about it because of course as you were stating before, so many of us find ourselves in a situation where every day we're not getting enough sleep. So we're functioning basically in a sleep-deprived state.

And we know what happens in the brain when a person or an animal is awake, and we know what happens when they're asleep, but there hasn't been much work done before on what happens when you're forced to stay awake.

And it was - as you mentioned - done then by implanting electrodes in the brain and actually watching the single cells or what they call single units, their behavior when they're awake, asleep and then forced to stay awake.

And the amazing result was that the individual cells starting showing the physiological signature of sleep, even though the animal was awake, even though the brain, if you were measuring overall brainwave activity, was looking like an awake animal.

And so many of us find ourselves in that situation, exactly. I think that this work is very important for that reason.

FLATOW: Yeah, I think - when I read this study, it asked - it raised a lot of questions with me. For example, maybe that is the normal state. Maybe there are always cells that are putting - going into neutral, you know.

Dr. COLWELL: Right.

FLATOW: Sort of waiting to be needed.

Dr. COLWELL: Yeah, I think that's a great concept, and it's one of the things that - so work in my own group, we study sort of the daily circadian cycle of cells, and cells do act differently between the day and night.

But you're absolutely right that if you're looking at a population of cells, there are some that will sort of be more like in the day state and some like in the night state. And I think this is exactly what's happening.

There's probably a small number of cells that are - when you're awake that are sort of in this physiological state of being at rest. However, most of them are clearly awake. And then in transition to sleep, you know, most of the cells are in this - on the sleep state, undergoing these slow oscillations that we characterize as sleep in humans.

But, you know, under these sort of stressful conditions, I'm sure, yeah, we find ourselves in them probably every day. We're getting an increasing number of the cells moving into the sleep state and that could potentially - it doesn't prove it - but it could potentially explain the decrease in performance that is so common in humans and other animals when we're not getting enough sleep.

FLATOW: Is there a tipping point where, you know, this is - you need this amount of sleep, or else you're really going to be malfunctioning?

Dr. COLWELL: Yeah. That's a great question. So for most people, there is a range. Of course, it's like a bell-shaped distribution, a normal distribution, right. So most people, though, do need about eight hours of sleep. And this can actually be documented especially in vigilance tasks.

Humans, if they're not getting enough sleep, really perform poorly on vigilance tasks. So think of those air traffic controllers, for example. And so as you're moving down to six hours, performance decreases on those tasks, six hours of sleep a night.

If you move all the way down to, like, four hours of sleep per night, then you start getting a number of neural endocrine changes in your body. So basically your stress levels go really high, your performance goes down, and you really get serious physiological changes with four hours.

But most people aren't at four hours. Most people are more like at the six-hour stage, where you see some decrease in performance but generally are getting through our days fine.

FLATOW: And in your studies, or in the studies you're talking about and the ones that you know of, what area of the brain is being - you know, going to sleep in this phase? Is it the thinking part? Is it the movement part or a little bit of all those places?

Dr. COLWELL: Right, so generally all of the brain is - moves into a different state when you're fully asleep. There's sort of different patterns, depending exactly on where you're talking about. But mostly for humans, we've been most concerned with our cortex, you know, the thinking part, but also the parts that control movement.

So the brain, when - our brain, when we're asleep is not silent but moves into these sort of slow oscillations that you can measure with EEG electrodes, and that's what defines sleep for us.

Of course, motor pattern - the motor pathways are normally shut down, or else you would be out, you know, sort of as someone who experiences sleepwalking or something like that would - sort of that is the part of the brain that controls motor pathways not being fully shut down. But normally, that would be shut down.

FLATOW: Here's a tweet that came in from Shandy's Ghost(ph), who says: Forget rat brains. Sleep specialists, especially in narcolepsy, have studied microsleep and autonomic actions for years.

Dr. COLWELL: Right, okay, so to be clear, one of the things which is different about this is that the rats in this case are not asleep. So it's not - they did careful video analysis, the experimenters who were doing these experiments, to really prove that the animals weren't moving into microsleep but were awake by all sort of normal criteria.

Yet the individual cells within the brain were starting to move into the sleep state. So it's a clear - it's a distinction from the microsleep.

FLATOW: And where would the next extension of this research go?

Dr. COLWELL: Okay. Well, there's a couple areas that I think would be really cool to see followed through on. One is to see whether this happens in humans. This would be very difficult but probably possible.

There's a few groups around the world that, recorded from the cells of the human cortex for patients that are undergoing surgery for epilepsy. So they have to sort of map out the focal point for the epileptic discharge.

And they do these recordings, and I think it would be possible, this is not my area exactly, but I think it would be possible for them to see whether the same sort of phenomena was occurring in the human brain when the humans are sleep-deprived.

And I guess as imaging technology gets better and better, right now of course we can't resolve down to see the activity of single cells, but in the future this is quite possible. So I think that's one area.

On the experimental side, what would be great is to show that - so they showed a correlation in this study between the individual cells moving into this sleep state and a decrease in motor performance.

But that's not really proof, and so what would be ideal is to move - to be able to experimentally move the cells into the sleep state. And increasingly, this seems to be possible as a number of groups around the world are developing these techniques to put in a genetic construct into small groups of cells in the brain where you can optically either increase their activity or decrease their activity.

So I think it would be possible to actually start asking: What if you move a group cells into the sleep state?

FLATOW: I'd also think that some of the question it raised in my mind were: Could the fact that we now know that some brain cells are going to sleep, might they explain us losing focus or attention deficit problems or things like that?

Dr. COLWELL: Yeah, absolutely. I mean, it's - again this is a rat study, and we always have to be a little bit careful in extending it to humans. But nevertheless, I'd say there's no reason to suspect that similar things aren't occurring in the human brain, although that needs to be proven.

And absolutely I think that your tweeter, I guess, you know, had brought up the issue of narcoleptics, where you have, you know, basically moving into the sleep state at inappropriate times of the daily cycle. And sure, this could be part of one of the things which is going on in those patients.

FLATOW: Let's see if I can get one quick call in from Dwayne(ph) in San Antonio. Hi, Dwayne.

DWAYNE (Caller): Hi.

FLATOW: Hi there.

DWAYNE: I had a rather unusual situation when I was going to college. I was taking a full academic load, and I was working also. So I wasn't getting much sleep. And I found that I was falling asleep with my eyes wide open in a lecture hall for 45 minutes to an hour, but when I woke up, I was refreshed, and I had retained and comprehended all the information that the professor gave in his lecture.

FLATOW: Wow.

(Soundbite of laughter)

FLATOW: I think they want you in a sleep lab someplace.

Dr. COLWELL: That's a great skill that I think - actually, I feel that many of my students do that in the lecture hall. So I'm with you, Dwayne. They, you know, they seem to have their eyes open, and yet sometimes I think they're fully asleep.

FLATOW: It just shows you how much we don't understand about the human brain, how the human brain is constructed, how it works. We're finding out new things all the time. Thats always surprising.

Dr. COLWELL: Yeah, in the sleep field, of course, one of the big things that we don't know is, really what is the function of sleep. And there's a number of different, you know, sort of models and hypotheses, but we really don't know what the function is.

A bunch of studies, you know, we can really document all the things that go wrong if you don't get enough sleep, but we really don't know, you know, what the function of it is. And so that's really one of the great mysteries, given that we spend so much of our time asleep every day.

FLATOW: Well, when you go to sleep, do your heart muscles rest, other cells in your body fall asleep? What happens there?

Dr. COLWELL: So that's a great question. So that's exactly one of the things that my field of circadian rhythms studies so much because we do - it does appear that the cells throughout your body, in your heart, in your liver, your pancreas, kidneys, as well as the brain, go through these daily cycles of - I wouldn't call it sleep.

We don't call it sleep at sort of the single cell level in my field. But they go - definitely they're in a rest state, and one of the things that I think happens, like for a human when we're in our night - in our sleep state, the cells are actually resting and going through repair mechanisms.

So they're fixing all the damage that we've done to them during the day, and even the - you know, the transcription, turning on and off of single genes changes from day to night in the cells throughout our body.

FLATOW: Okay, we're going to have to leave it there. Thank you very much, Dr. Colwell.

Dr. COLWELL: Okay, I appreciate it.

FLATOW: Take care. Christopher Colwell is a neuroscientist and professor in the Department of Psychiatry at UCLA Medical School. When we come back, we're going to take a break first and then talk about "Blood Work: A Tale of medicine and Murder in the Scientific Revolution" in the scientific revolution with Holly Tucker. Stay with us. It's a really interesting book. We'll talk about it. Our number is 1-800-989-8255. Stay with us. We'll be right back.

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FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.

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