... What do these tests mean that we saw you doing today?

Well, basically there were two different kinds of tests -- the ball and cup, and the pursuit rotor. They were basically motor tasks that weren't really too complicated. Conceptually they were easy to do. It's just a matter of doing them faster and more accurately. Those two tasks were different than the mirror trace. The mirror trace required the subjects to come up with a brand-new way of handling the situation. ...

Now the skills tasks we found require stage 2 sleep, continuous stage 2 sleep. If you don't let people have enough of it, or if you let people have as much as they would have in a night but you interrupt it so that it's not continuous stage 2, the amount of progress that people make in learning skills tasks is retarded. They simply don't remember the next day as much as if they had had a full night of stage 2 that was uninterrupted.

The other task requires some kind of new cognitive solution to the problem. This is different than the other two, and this required REM sleep. And as you saw, one of the subjects got lots of REM sleep over 100 minutes and the other got 44 [minutes], I believe. That's clearly not enough. The person who got over 100 minutes of REM sleep actually improved by 44 percent. It's remarkable -- she was much, much better the second time around.

The person who didn't get enough REM sleep was actually a little bit worse -- we could say, at very worst, did not make any progress beyond what they had made before. That's remarkable. There's an almost 50 percent gap, 54 percent gap between what the one did who got enough sleep and what the other did.

So we have two different kinds of tasks. Each appears to have its own neural system, and I suppose in a day of learning, you would run into both these kinds of tasks. Certainly young people do. ...

What is happening actually inside the brain? Is what they learned being reinforced?

We have several sources that suggest what is happening. For example, during REM sleep in animals, the things that were being carried out while the animal is awake, the neurons that were firing in certain patterns, are again firing in those same patterns during sleep. It's called the replay phenomena, where during REM sleep and only REM sleep this activity continues. It's like the brain is doing some further rehearsing, practicing, finishing up; we don't know exactly what the word would be, but clearly it's doing it again.

I've been involved in some work with some people from Belgium. We ask people to sit in a PET scan while they were learning a serial reaction time task. ... It was a complicated task. We saw that there were certain parts of the brain were very active while the subject was learning the task, and then we let them sleep. ...

We noticed that during stage 1, 2, or 3 and 4, there wasn't really very much going on. But during REM sleep, for this cognitive task, those parts of the brain that were active while the subjects were learning were again active during REM sleep. It's another kind of demonstration that here is a replay going on or rehearsal, whatever you want to call it. Certainly more of the same is going on while the subject is sleeping.

Does that mean that people get better at something that they've done before they've slept? Can you just describe what's happening?

... Absolutely. Absolutely. In studies where people are simply allowed to sleep after they do the study, you see this jump in performance that's quite remarkable, and in skills tasks, as well. There is an increase in performance that's not just a free gift. But a good night's sleep will get you this jump in performance that you would have to work very hard during day time to keep up with. ...

In the case of the cognitive tasks, one of the things that happens is that the number of the density of eye movements goes way up. The number of minutes of REM sleep doesn't necessarily change, but the number of eye movements really does go up. It can often double. [This shows] that there's a great deal more intensity -- maybe more work going on, if you want to put it that way.

In animals, you'll often see increases in the number of minutes of REM sleep. And in other studies [that] people have done in humans, you see an increase in REM sleep as well. So the task actually seems to induce more REM sleep.

Of course, if it's a task that doesn't involve REM sleep, there'll be no change. Recently we've also seen some subtle changes in stage 2, if the task happens to be a skills task. So it's another kind of design. But you can look at sleep in that way, and you can see these changes that are actually in the sleep patterns themselves. There's a change in sleep architecture. ...

How important is sleep for learning?

... If you want to make a lot of progress, you simply have to have it. People vary in terms of how much they need. But if I had the choice between staying up a few more hours and trying to get the drop on or get ahead of someone who was going to bed, I wouldn't even bother. Certainly the sleep is more important than those extra hours sometimes. You have to have it.

Compare consistently getting a good night's sleep to some other things that parents might do for their children.

After you've got a student who's got reasonably good study habits, and who's got the important things like enough to eat and all the basics of comfort, I can't think of anything more valuable that you could get someone to do than give them the information that a regular schedule of going to bed, and getting up as opposed to cheating yourself out of another couple of hours to watch a late night talk show or something. ...

One of your colleagues compared this to students that had good SAT scores, students who had been to good prep schools, students who had been tutored extensively. Can you just talk about that kind of comparison?

Yes, I actually remember a conversation with my friend. In fact, he articulated it best when he simply said that the best predictor of how well someone is going to do be they at Harvard or wherever is not their SAT scores or anything else; it's whether or not they get a good night's sleep. And I have to agree with that. ...

How important is this sleep deficit in our society -- particularly for students?

In the studies that we've done where we deprived people even of a partial night of sleep, we saw deficits that go from anywhere from 20 percent to 50 percent. I can only think that if you do that as a lifestyle -- imagine taking a course and you've got a friend who goes to bed every night and who never parties, and there's you. The two of you are going along, and every day he remembers even 20 percent more than you do. At the end of a month, you can add that up. Imagine how far this person is going to be ahead of you. ...

The special worry with teenagers is that they are learning a tremendous amount. They're still learning a lot of motor skills, fine motor skills, as well as learning all sorts of new cognitive procedural material. There's no end to how much they can learn. They can be overwhelmed with how much they need to learn. On top of all that, they're still growing.

Since sleep is important for all of those, a young adult would be crazy not to get some sleep. You need sleep for growth. You need sleep for lots of other reasons that we probably don't even know about. This isn't the only reason that that you have stage 2 and REM sleep. But clearly one of the functions is to consolidate these tasks and accelerate, make it more efficient. Your learning is much more efficient if you have a good night of sleep -- that's maybe the best way to describe it. ...

[How do you feel about the teenage pattern of sleeping late on the weekends?]

Sleeping in is one of the best things that can happen, and I have always argued that you should leave them alone. If they really feel like sleeping in, they probably need that sleep. Later on, when they become young adults, that will probably disappear. But often, when they're learning a great deal and trying to keep up with their peers and so on, they're often stretching almost to the limit of what they can do. And sleeping in is one of the best ways they can do to sort of stay abreast of what's going on. Let them do it. ...

[What is the message that you want to send out to people?]

When you're learning something that is cognitively very difficult and very new, and you do get a grasp of it, you can do nothing better than go to sleep. [It's] the only way that you'll make any real progress.

One of the things that students sometimes do, having not opened say their physics textbook until the night before the exam, will say, "Hmm, I'm going to have to stay up all night to get this stuff under control." And chances are they will not get anything under control. They'll go on to the exam, they'll be tired, they will not have understood enough of it to really pass. This is something that takes time.

You've got to learn some; you've got to sleep some; you've got to learn some more; and it builds. There's certain kinds of material that are difficult enough that you could only do it this way. This is not simple memorization. This is stuff that requires you [do] some real cognitive work. And if you're going to learn that material, you're going to have to get some sleep. ...