IRA FLATOW, host:

Birds do it. Bees don't. We do it more than elephants, but less than bats or opossums. What am I talking about? Of course, I'm talking about sleep--something you can't do without, yet few of us, it appears, get enough of it.

Writers, poets and scientists have pondered this mysterious state of consciousness for centuries, asking questions like: Why do we even need to sleep? Why would evolution favor sleep? Think about it. When you're asleep you're in your most vulnerable position. You're unable to defend yourself from an enemy. So what's the payoff here? Are there crucial biological functions that can only take place when we sleep? And if so, what happens when you don't get enough sleep? Does memory suffer? Do--are there deep psychological things that are going on when we sleep that we--maybe we don't even know about?

A lot of people, including myself, can report that they certainly are not getting enough sleep. Whether it's restless leg syndrome or sleepwalking, what's keeping you up at night? And I don't need to know all of your personal problems; just talking about, you know, what kinds of things--what kind of sleeping problems you may be having, 'cause that's what we'll be talking about for the rest of the hour. And if you want to get on that conversation, give us a call. Our number is 1 (800) 989-8255; 1 (800) 989-TALK.

Let me introduce my guests. Robert Stickgold is associate professor of psychiatry at Harvard Medical School. He has joined us many times on SCIENCE FRIDAY, and he's in the studio on the campus there.

Welcome back. Dr. Stickgold.

Dr. ROBERT STICKGOLD (Harvard Medical School): Thanks, Ira. It's a pleasure to be back.

FLATOW: Thank you. Carlos Schenck is a senior staff physician at the Minnesota Regional Sleep Disorders Center in Minneapolis. He joins us today.

Thank you for being with us, Dr. Schenck.

Dr. CARLOS SCHENCK (Minnesota Regional Sleep Disorders Center): It's my pleasure.

FLATOW: Let's talk about a definition first, Dr. Stickgold. What is sleep? And why do we sleep?

Dr. STICKGOLD: Two hard questions. Sleep in most cases is simply defined as a period where we become behaviorally inactive and unaware of the environment around us. It's similar, in fact, to conditions like coma, except that it's natural and reversible. That's probably the easier of the two questions.

The question of why we sleep is one that we continue to struggle over. There are probably many, many things that are occurring during sleep that are beneficial, things that have been assigned by evolution to that part of the night. My own personal favorite, and the one that I think has the best explanation for why it would have evolved originally, is that while we're asleep the brain is going through our memory storage and trying to see what's worth keeping, what's worth throwing out, and how things should be strengthened and put together.

FLATOW: Mm-hmm. Well, would you agree with that, Dr. Schenck?

Dr. SCHENCK: I would, and I think Dr. Stickgold's research is very important in that area in terms of memory consolidation. So I cannot dispute that at all.

FLATOW: Is there something in the body that you use up during the day or you accumulate that makes you have to sleep, Dr. Schenck?

Dr. SCHENCK: Well, that's a major point for debate. There may be some type of protein accumulating that will promote sleep, that will then set off a chain of kind of reactions in the brain and the whole biochemistry to help regenerate our tissues, for example, and allow us to feel refreshed in the morning.

FLATOW: Yeah.

Dr. SCHENCK: That's the bottom line of sleep, as well. How do you feel when you wake up in the morning? And that's really, as a clinician, something that we focus on in terms of the functional consequence of any sleep-related complaint. How do you feel in the morning? If someone says, `I don't think I'm getting enough sleep,' and yet they wake up refreshed and they function, they may be a short sleeper and may not need nearly as much sleep as the average person. So you always have to focus on the functional consequence.

FLATOW: So how do you know, then, that--if you're getting enough sleep in the morning? Just that you feel refreshed when you wake up?

Dr. SCHENCK: Exactly. And how do you function at home and at work? Do you get any kind of negative feedback from people in your life that you don't look well or that you seem to be irritable or some kind of other sign that you're not up to par?

FLATOW: Yeah.

Dr. SCHENCK: But if you are, then you are probably getting enough sleep.

Dr. STICKGOLD: With the one caveat that if you need a double grande to get that morning going, then you're probably not getting enough sleep, right?

Dr. SCHENCK: Absolutely. Yeah. Yeah, you always have to focus on caffeine intake throughout the daytime, beginning in the morning. That's true.

FLATOW: Well, let me, you know, dwell on that point a bit, because could the problem be that we're getting too many of those grande lattes, super cappuccinos during the day, and that's keeping us from sleeping at night?

Dr. SCHENCK: Absolutely. And there's another ominous event that's taking place now, and that is there are new beers on the market that are loaded with caffeine, and so people will drink a beer in the evening and the caffeine makes them feel more alert, and yet it will greatly prolong their onset for sleep, and that could have a devastating effect on their sleep-wakefulness rhythm.

FLATOW: I have never heard of this before. Is that right?

Dr. SCHENCK: There's a whole--oh, the competition is out there. You'll be hearing more and more about these type of beers loaded with caffeine.

FLATOW: Wow. You know, theoretically, you don't--you're trying just the opposite, to let you--you know, I'll have a drink before I go to sleep and then I'll sleep better.

Dr. SCHENCK: Well, they want people to drink a lot of alcohol and not feel sedated, and that's where the caffeine comes in. I think it's really going to have a very devastating effect in a number of ways. But the combination of alcohol...

FLATOW: Right.

Dr. SCHENCK: ...in terms of beer and caffeine is on the horizon.

FLATOW: If you don't want caffeine to affect you, keeping you awake, what time of day should you have your last cup of caffeinated coffee or soda that's laced with caffeine?

Dr. SCHENCK: Well, everyone is different. The half-life of caffeine in the blood is about three and a half hours, so if you have great sensitivity to caffeine then, really, noon should be the cutoff, and have no more than one or two cups in the morning. Other people are less sensitive and they can have a cup in the afternoon. But certainly not after dinner.

FLATOW: Dr. Stickgold, let's talk about some of your sleep and memory studies, because they've been wonderful. You've been coming on over the years as you learn more about sleep and memory. I remember one of the first times you came on, you told us that there are certain skills that you could learn during the day, but if you don't get eight hours of sleep you don't cement them.

Dr. STICKGOLD: That seems still to be true.

FLATOW: And I said to you at that point, `Well, I never get eight hours of sleep anymore,' and you said, `That's why you're not learning anything,' so to speak.

(Soundbite of laughter)

Dr. STICKGOLD: Well, it's unclear that--you know, those studies in particular were looking at improvements over one night, and actually on a task where we show that you continue to improve from an initial training over the second and third and maybe even the fourth night. So it might be that you can add nights together if need be. But it's this very tricky situation where people are not aware of failures of memory improvement that might happen if they don't get enough sleep. So if you're trying to learn the piano and you can't particularly master a passage one day, it's not uncommon to come back the next day and sit down, and first time through you seem to have it perfect. And we've done studies with a finger-tapping test that show you can get a 20 percent increase in speed and a 30 percent decrease in errors just as a result of a night of sleep.

Now if you don't get enough sleep and you come back the next day and you're performing, you know, with as much frustration as the day before, you don't notice that as a memory problem. You don't say, `Well, jeez, my sleep wasn't good enough.'

FLATOW: Yeah.

Dr. STICKGOLD: So--but the evidence just keeps seeming to build up that that sleep is really critical for a number of types of memory consolidation, but maybe least for the one we're most aware of, which is simple facts.

FLATOW: Oh.

Dr. STICKGOLD: So, you know, when I talk about sleeping on a problem--if I can't remember someone's phone number, I would never say, `Let me sleep on it.' That doesn't seem to be what sleep is most critically involved with. It has more to do with putting things together and coming up with new combinations of memories that seem to be appropriate to put together than with just a strengthening of simple what we call declarative facts about our day.

FLATOW: 1 (800) 989-8255 is our number. We're talking about sleep this hour with Dr. Robert Stickgold and Dr. Carlos Schenck on TALK OF THE NATION/SCIENCE FRIDAY from NPR News.

Dr. Schenck, what is the number one sleep disorder that you see in your clinical work?

Dr. SCHENCK: Well, at the Minnesota Regional Sleep Disorders Center, we're a multidisciplinary sleep center, so we take all comers, and certainly the insomnia complaint--not getting enough sleep, not feeling refreshed upon awakening in the morning. And there are many, many causes responsible for that complaint, but insomnia certainly is number one. Number two would be feeling too sleepy during the daytime, and that could be a result of a hard-core sleep disorder, or it could be a result of lifestyle choices, where people voluntarily choose to sleep less than they need to.

FLATOW: Right.

Dr. SCHENCK: They think sleep is an option. Sleep is not an option; it's a necessity.

FLATOW: Is there any one causative agent or problem at night that people who want to sleep can't go to sleep? I know a lot of times I have problems 'cause I just can't shut my mind off--you know, that sort of thing. And I see now that the drug companies are more than happy to sell me a drug for that, so...

Dr. SCHENCK: Well, you know, a clinician really has to investigate very carefully, have the patient play detective...

FLATOW: Right.

Dr. SCHENCK: ...along with you to identify the possible causes because you may have a primary insomnia disorder. There are people born that way. They come from families full of insomniacs. Other people drink caffeine too late or drink too much alcohol or a medication for a medical disorder or a psychiatric disorder--many, many possible causes, but certainly, voluntary decisions to stay up late, to burn your candle at both ends is a major issue that you have to address.

FLATOW: 1 (800) 989-8255. Let's go to Luba in Groton, Connecticut. Hi.

LUBA (Caller): Hello.

FLATOW: Hi there.

LUBA: Well, you haven't touched on the restless leg syndrome, but I heard in the beginning that you were going to mention and talk about it.

FLATOW: That's why we have you here.

LUBA: And what I'd like to say about it is that all of a sudden it's become a prominent subject on television and in advertisements, and I think that the solution or the medications that the doctors are proposing is not really the proper medication for it.

FLATOW: Do you have that?

LUBA: Yes, I do.

FLATOW: And it keeps you up at night obviously?

LUBA: Well, no. What happens is, is that when you settle down in the evening and, you know, like watching TV or whatever, you constantly feel like you have to move. And what happened was that my husband was riding on the commuter train and he found an article in The New York Times--this was about three years ago--and it was a full-page article about restless leg syndrome and he came home and said to me, `Is this what you have?' because I had problems with my legs for several years. And basically the bottom line is that it's a--you have a very low iron in your system.

FLATOW: Let me ask--I have a clinician here. Dr. Schenck, what's the formal definition?

Dr. SCHENCK: Well, the restless leg syndrome is really a neurologic disorder affecting your sleep where supposedly sleep-related dopamine levels in the brain become diminished and results in the symptoms that are very severe, of very uncomfortable feelings in the legs. The legs feel like they're jumping around, and the only way to relieve the uncomfortable or even painful sensation is to move around, and that's incompatible with falling asleep. The low iron comes in actually in patients who respond very well to medication, and then the medications no longer work and then the clinician must look into a low iron level because that could be responsible for the lack of response to treatment. But the ultimate cause of restless leg syndrome is really not so much a low iron level; most people who have anemia or low iron don't have restless leg syndrome. But you have to have a predisposition to restless leg syndrome and if you have low iron, that makes you very unresponsive to treatment.

FLATOW: Thank you, Luba. Why are we just now seeing medications for this if this has been an old ailment?

Dr. SCHENCK: Well, there have been medications for many years, but now that we know the much more precise cause of low sleep-related dopamine, the logical solution are medications that increase brain dopamine, and those have come on the market relatively recently.

FLATOW: We're talking about sleep this hour with Robert Stickgold and Carlos Schenck, and we're going to go away and take a break and come back to take more of your calls. If you want to know about sleep problems or maybe the mechanisms of sleep, we'll talk a bit about what may be going on in your brain during sleep. So stay with us. We'll be right back after this short break.

You're listening to TALK OF THE NATION/SCIENCE FRIDAY from NPR News.

(Announcements)

FLATOW: You're listening to TALK OF THE NATION/SCIENCE FRIDAY. I am Ira Flatow.

We're talking this hour about sleep with my guests Robert Stickgold, associate professor of psychiatry, Harvard Med School; Carlos Schenck, senior staff physician at the Minnesota Regional Sleep Disorders Center in Minneapolis.

Dr. Schenck, tell us about something called RBD, REM sleep behavior disorder.

Dr. SCHENCK: Well, the second patient that I saw at the beginning of my career in 1982 was an older man who complained of violent moving nightmares, and in the sleep lab he had something that was unprecedented in that he did not have the paralysis of the muscles during rapid eye movement sleep that is present in all mammals. And during that stage he was becoming very vigorous and violent, and that correlated with his clinical history of flying out of bed, having football dreams, crashing into the furniture and getting hurt. And that really ushered in a new era in the sleep behavior disorders where we now realize that men over the age of 50 are particularly vulnerable to this condition that often is associated with a neurologic disorder and particularly Parkinson's disease.

FLATOW: So you mean it might be a symptom of Parkinson?

Dr. SCHENCK: Exactly. What we found in following these patients for many years is that on average in 13 years 65 percent of these men developed Parkinson's disease, but the very first sign of the Parkinsonism was a behavior disorder during sleep, and not only that, a dream disorder. These men were acting out distinctly altered and violent dreams. So it's fascinating in the terms of the science, but also quite sobering in terms of the clinical medicine that you have to now inform these men that they are considerably high risk for eventually developing Parkinsonism.

FLATOW: So this has now become--this is very interesting. Sixty-five percent, you said.

Dr. SCHENCK: Of men age 50 and older who come in and were documented in the sleep lab to have the REM behavior disorder or RBD where they lost the muscle paralysis of REM sleep will go on on average in 13 years, but it could be in two years or it could be in 29 years, will develop Parkinsonism.

FLATOW: Is it possibly related to restless leg disorder that this...

Dr. SCHENCK: People have asked that question and fortunately the answer is no. There is absolutely no correlation at all. The dopamine problem with the restless legs is different from the dopamine problem in Parkinson's disease.

FLATOW: Dr. Stickgold, what--let's talk a bit about what's going on in our brains and your study of people when they're sleeping. When you're studying people sleeping and they report on their dreams, how do you know that they're giving you an accurate description or that they're remembering something that they actually dream?

Dr. STICKGOLD: Well, in some ways we can't know that. We can't know that any better than when a physician takes a history that the patient is giving an accurate history. So at some level we just have to do a combination of going on faith and looking at actually our own dreams that we have ourselves as researchers and compare them to what we see reported by other people.

But beyond that, there are a number of ways that you can start to get at this question, and one is, for example, you can ask the question, well, how does the presentation of the dream relate to the state of the brain at the moment. So what has been found in study after study, ever since the '50s, is that if someone awakens from REM sleep, they're much more likely to report a dream, and as the night gets later the dreams tend to become more intense and longer and more bizarre in their description. And even down to microscopic level--'course, REM sleep is rapid eye movement sleep, and those rapid eye movements come in bursts that last a couple of seconds and then there's a pause. If you wake people up right in the middle of a REM eye movement burst you get more intense and more frequent reports than if you do at--even five seconds or 10 seconds later. So it looks that it really is a fast time constant between what's going on in the brain and at least overall on average the amount of dreaming that's reported.

FLATOW: Is--does the brain go to sleep when we go to sleep, so to speak?

Dr. STICKGOLD: Well...

FLATOW: Is brain activity reduced when we go to sleep?

Dr. STICKGOLD: In--during parts of sleep it is, and in parts it's not, so when we have what's known as non-REM sleep and especially the deeper portions of that known as slow wave sleep, there's about, I think, a 20 percent reduction in total energy consumption by the brain, but it also varies by region and when you go into REM sleep, there are regions of the brain that are clearly more active even than they are during wake. And it's become very true that this image that most of us sort of grow up with that when we sleep our brain shuts down and just rests is actually very, very wrong, that the brain continues to be active and working all night long.

FLATOW: So we haven't really figured out, though, exactly what's going on--I mean, for centuries now everybody's trying to figure out what's going on when you sleep. You have figured out some of it, but not really all of it.

Dr. STICKGOLD: Oh, absolutely. There's a lot of progress lately. Cliff Saper and Tom Scammell here at Harvard have been doing some elegant work looking at the actual brain mechanisms that control sleep, so we're getting a much better handle on the switches and the controls that cause us to fall asleep and that regulate our sleep once we fall asleep. And lots of labs all over the country are looking at functions that range from immunological functions to endocrine functions to cognitive and memory functions, and we're starting to finally tease that apart. But you're absolutely right. Of all the basic mammalian drives like hunger and thirst and sexual drives and the drive to sleep, with the exception of sleep we understood the biological functions a couple thousand years ago, and with sleep we're still struggling over figuring out what they are.

FLATOW: Let's go to Dan in Buffalo, New York. Hi, Dan.

DAN (Caller): Hello. I was actually calling to interject that, you know, I always felt from the time I was a child and as early as I can remember up until through college--I always had a difficult time sleeping, getting to sleep. It was like a litany of ideas and things going through my mind, you know, constantly. Like--and sometimes it would become perseverative in that I'd have a song or some idea that I just couldn't get out of my head, and you know, it wasn't until I was diagnosed with a generalized anxiety disorder and started to control that with Paxil that I've actually had a lot of really good sleep, and I haven't had that problem in the last two years since I've been on an SSRI. I didn't know if these was anything to support that--SSRIs as a way of controlling anxiety.

FLATOW: Dr. Schenck?

Dr. SCHENCK: Well, yes. I think this comment is very appropriate because there are many potential causes for an insomnia complaint, as I already mentioned. One of them is anxiety or depression and certainly the control of the anxiety can then promote sleep, so I think this is a wonderful example of how a separate medical condition in this case, generalized anxiety disorder, promoted insomnia and the control of the anxiety disorder then allowed the restoration of sleep. And so you don't call Paxil a sleep-inducing agent; it is secondarily by controlling anxiety that was interfering with sleep.

FLATOW: Thanks for calling, Dan.

DAN: Thank you. Now I have a newborn, so I don't have anything that can control that, but...

Dr. SCHENCK: Enjoy. Enjoy.

FLATOW: Yeah, you're not going to sleep for 20 years so...

DAN: Right.

Dr. STICKGOLD: Let me just add one comment because I think this...

FLATOW: Yeah.

Dr. STICKGOLD: ...issue of these thoughts that intrude as we're falling sleep is one of the fascinating aspects of sleep that we don't understand at all yet. It's universal; even people without anxiety disorders--you mentioned it yourself, Ira; you go to bed, you gotta paper due tomorrow and you can make it all the way through the day without worrying about it, and then you lie down in bed and you close your eyes, and these images and anxieties just start going through your mind. They don't have to be anxieties. I mean, visions...

FLATOW: Right.

Dr. STICKGOLD: ...of sugar plums danced in their head. So excitement can just as easily--positive things as well as negative things can keep you awake in this period. My suspicion is that what's happening in this pre-sleep period is that your brain is starting the process of looking through recent memories to find what's important to process, and normally it does that with a pretty flat affect, but if the affect gets revved up by the thoughts, then you hit this thing--I mean, I think everybody's experienced where you're lying in bed and all of a sudden you think of something and you can feel sort of an adrenaline rush and you say, `Oh, no, now it's going to take me 10 minutes to calm down again.'

FLATOW: Right.

Dr. STICKGOLD: So I think that this is one of those aspects of the sleep transition that we really haven't studied as much as we should, and we see it at the start of the night, and when you get to my age, you get the 4:00 yah-yahs where you wake up. I woke up two nights ago and it was this sudden revelation that Sandra Day O'Connor has to withdraw her resignation, that that would solve all the problems we're having. And that was a clever idea, but then I lay in bed and went over and over it for about an hour just unable to go back to sleep. So I don't think we understand what it is about that state of our brain...

FLATOW: Right.

Dr. STICKGOLD: ...as we're near transition into sleep that causes it to come up with these emotionally laden concepts and just ruminate on them.

FLATOW: I've had times over the years where my most creative work was done when I could not get to sleep and something finally came out at like 2:00 in the morning. I could write a whole chapter of a book I couldn't write before, you know?

Dr. STICKGOLD: And there are...

FLATOW: And I learned to go with it. I would know years later something's going to happen tonight; let's just wait this out, and it happens. You know, that sort of thing.

Dr. STICKGOLD: Right. Thomas Edison used to problem-solve by sitting in a chair with his arm on the arm of the chair holding the spoon between thumb and forefinger over a tin plate, and he would just close his eyes and think about problems. And as he fell asleep the muscle tone would relax, the spoon would drop, wake him up, and he'd say, `Boom, OK, now I have my answer.' So what's actually happening there is one of those deep questions that I'm totally frustrated that I'm too stupid to figure out how to test.

FLATOW: Dr. Schenck, let's talk about some of these drugs that are being marketed on TV for people who can't sleep. They have incredi--if you read the warning labels on them, they say make sure you get eight hours of sleep--you know, you're not going to be doing anything for the next eight hours. They say you may lose your memory for certain numbers of hours.

Dr. SCHENCK: Yeah, it sounds scary and I think the manufacturers protecting themself or itself from any liability. Any medication has potential side effects, and certainly there are people who have a carry-over effect the next morning from a sleeping pill that could interfere with memory or make them feel drowsy or if they don't get eight hours, they may have some negative effect. But the reality is if someone is carefully diagnosed with an insomnia disorder, these medications should work quite well without any side effects. But obviously, you need good communication with your prescribing physician to give feedback right away about any adverse effect. But in general, these medications are very safe and well-tolerated.

FLATOW: Let's go to Rick in Waukegan, Illinois. Hi, Rick.

RICK (Caller): Good afternoon. How are you?

FLATOW: Hi.

RICK: Hey, I have a question about what happens to sleeping patterns--rather, breathing patterns when we sleep. I was told that somehow we're all shallow chest breathers and that it's more natural to breathe through our diaphragm and this is something we do automatically when we sleep? Is that right? And does that help us to breathe that way?

Dr. SCHENCK: Well, the diaphragm really helps the whole effort for breathing, but it's the whole upper airway system that's involved in breathing, in the nose, the mouth, the pharynx. So it's really a package deal that way.

FLATOW: All right, Rick. Thanks for calling. 1 (800) 989-8255 is our number. We're talking about sleep this hour on TALK OF THE NATION/SCIENCE FRIDAY from NPR News.

Which brings up--he had an interesting point about breathing. I'll take this in two directions. The first direction I want to go in is, you know, when you get to that point that you're about to fall asleep, you sort of notice that your breathing has become regular and you're going into a sort of a sleep pattern. Can you will this on yourself? Now if I, you know, change--can I make my mind-set change? I'll start to breathe regularly, maybe the rest of my brain will take over and put me to sleep? Dr. Stickgold, have you noticed this at all?

Dr. STICKGOLD: Well, I actually do that myself. If I have trouble falling asleep, I will slow my breathing way down. Now I haven't a clue why that helps, but it does. Carlos, do you have thoughts?

Dr. SCHENCK: You know, it's very interesting. When you look at the techniques used for teaching hypnosis or progressive muscle relaxation, the breathing is one of the key components where you're told to take nice, deep regular breaths. So I think breathing is a really key component with the whole relaxation process that can then facilitate sleep. So yes, you can have voluntary control.

FLATOW: And the other direction I'm going is sleep apnea here, because this is the other side of the coin where people think they're sleeping a full night but they're waking themselves up from stop--they stop breathing regularly.

Dr. SCHENCK: Well, the prevalence of obstructive sleep apnea in adults is up to 3 percent and it correlates with obesity, but also other factors. And unfortunately, these people are completely unaware of how often they may have awakenings during the night to stay alive and breathe. They could have a hundred times an hour repetitive arousals to breathe and get their oxygen level up to normal, and the devastating effect is the next day they're wiped out, tired and sleepy because they don't have good continuous sleep. It's up to the people in their bed or in their lives to say, you know, `You're not sleeping and look at the effect on you.'

FLATOW: Is it possible that some sudden deaths in the middle of the night can be just from the failure to start breathing again?

Dr. SCHENCK: Almost never. It's extremely rare. People with obstructive sleep apnea will eventually, and it's scary in the sleep lab--we'll see two minutes, three minutes--but they will wake up. They could sometimes have heart rhythm problems--bradycardia--that could have an adverse effect, but people don't die from sleep apnea in their sleep. They die from the consequences in terms of high blood pressure and other adverse effects.

Dr. STICKGOLD: What about SIDS? Is SIDS thought to be breathing now or cardiac?

Dr. SCHENCK: It's still an open question.

FLATOW: 1 (800) 989-8255. Let's go to Helene in Paramis, New Jersey. Hi. Welcome to SCIENCE FRIDAY. She's gone. Let's go to St. Louis. Go to Ron in St. Lou--well, if I get the phone to work. Ron in St. Louis, are you there?

RON (Caller): Yes, I am.

FLATOW: Hi. Go ahead.

RON: Thanks for taking my call. I know we don't have much time. Two quick questions I've been wanting to ask for a long, long, long time. I read many years ago a book by Professor Perez Levi(ph) from Dedechnion(ph) in Israel about dreams and sleep, and he said basically you can get used to sleep less, you know, even five hours a night and should be OK. Now NASA in the space station requires eight hours of sleep from the astronauts. So the question is, is it really true that five or six hours of sleep could be enough for people. Second question...

FLATOW: I only have time for one question.

RON: OK.

Dr. STICKGOLD: Well, let me go first. The answer is no. There are people for who five or six hours of sleep might well be enough, but in general, if you bring students into the lab and put them down to six hours of sleep a night--and David Dinges in Pennsylvania has done this--for a period of, say, three weeks on six hours a night, six hours of sleep a night after three weeks--people start behaving the same way they do after two nights with no sleep at all. So although they don't feel like they're getting worse and worse, their performance on simple tests like a vigilance task where you hit a space bar whenever you see...

FLATOW: Right.

Dr. STICKGOLD: ...a target on the screen, their performance will continue to deteriorate for at least three weeks, if they're actually on as little as six hours and statistically even eight hours of sleep...

FLATOW: I've got one quick question and I need 20 seconds. If you lose a lot of sleep, can you recover? I mean, or do you have--is there a sleep deficit that you have to make up?

Dr. STICKGOLD: You do make up sleep that you lost. It is important to make up sleep that you lost, but some of the deficits that resulted from that sleep loss can't be regained by making it up at another time.

FLATOW: All right. There we go. We've run out of time. Robert Stickgold is associate professor of psychiatry at Harvard, and Carlos Schenck, a senior staff physician at the Minnesota Regional Sleep Disorders Center in Minneapolis. Thank you for talking with us today.

Dr. STICKGOLD: Always a pleasure.

Dr. SCHENCK: Thank you very much. I appreciate it.

FLATOW: Have a good weekend.

(Credits)

FLATOW: And as always, you can surf over to our Web site at sciencefriday.com where you can find our podcasts there. Also, SCIENCE FRIDAY's Kids' Connection is there; just click on the teachers button on the left side and you can download free teaching curricula that we use at SCIENCE FRIDAY. If you missed any of the comments or what we made today, you can surf over to our Web site and find all the links to the topics we talk about on SCIENCE FRIDAY.

Have a great weekend. We'll see you next week. I'm Ira Flatow in New York.

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