Memory And The Dreaming Mind
If you’ve ever stayed up too late studying for a test, you know that sleep impacts memory—you need that precious shut-eye in order to encode and recall all that information. But what is it about sleep that aids memory?
Researchers have pinpointed a specific stage of sleep, REM sleep, as an area of interest for studying memory consolidation. REM, or rapid eye movement sleep, is the same stage in which dreams occur. So researchers at Northwestern University devised a way to communicate with lucid dreamers—people who are aware of their dreams and can control what they do in them—as a way to study how memories get made.
Science Friday producer Katie Feather talks with Ken Paller, professor of psychology at Northwestern University to discuss what lucid dream research has taught us about memory.
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Ken Paller is a brain, behavior, and cognition professor at Northwestern University at Evanston, Illinois.
IRA FLATOW: This is Science Friday. I’m Ira Flatow. Have you ever had a lucid dream? You know the kind where you know you’re dreaming and can control what goes on in the dream. Researchers are studying how to communicate with lucid dreamers while they’re sleeping. Yeah, as a way to study how memories get made. SciFri producer Katie Feather shares more.
KATIE FEATHER: If you’ve ever stayed up too late studying for a test or cramming for a morning meeting– and let’s face it, we all have– you know that sleep impacts memory. You need that valuable shut-eye in order to encode and recall all that information. But what is it about sleep that aids memory?
Dr. Ken Paller of Northwestern University is a memory researcher. But in his most recent study, he took a turn to study lucid dreaming. And he joins me now to talk about why. Dr. Ken Paller, welcome to Science Friday.
KEN PALLER: Thank you, Katie.
KATIE FEATHER: So what’s the working definition of a lucid dream? It’s more than just a dream you remember, right?
KEN PALLER: Right. A lucid dream is one step beyond that. It’s during the dream understanding that it’s a dream that’s happening at the moment. And the majority of dreams are ones where we think we’re awake. We think it’s reality. We think things are going on as usual. Even though bizarre things might happen, we don’t always have the realization that we’re dreaming. We think we’re awake. So a lucid dream is purely defined as saying, well, if you understand that you’re dreaming, that’s a lucid dream.
KATIE FEATHER: Sometimes I find myself towards the end of a dream after much has happened, and there’s no sense that I’m dreaming. Something will happen, and I’ll be like, wait a second, this would only really happen in a dream. I think I’m dreaming. And then moments later, I’m awake. Is that a lucid dream?
KEN PALLER: It sure is. It’s just a very short one. So the lucid dreams get more interesting if you manage to stay in it and continue to explore what’s going on because you can take another step, which is to try to influence what happens. You can decide where you want to go, who you want to meet. And sometimes the dream goes along with your wishes and it happens, though not necessarily.
KATIE FEATHER: So as a memory researcher, how do you find yourself doing a study on lucid dreaming?
KEN PALLER: Yes, my research is quite a different topic. I’ve been studying memory my whole career. And so I’m interested in how memory works, how do we remember things. And I’ve looked at what happens when you first learned something new. What happens when you retrieve it later. And I also got interested in what happens in this intermediate time.
So learning isn’t something that just happens instantly the way you put a file on your computer. But often information doesn’t stick in your head unless you practice it. And the interesting part, now, relating it to sleep, is that some of the rehearsal that makes our memory work happens when we don’t realize it while we’re sleeping and information that we’ve recently learned comes up. It gets reactivated at night and therefore integrated better and more available when we wake up the next day and we need to remember things.
But we don’t realize we’re revisiting information during our sleep because it’s not necessarily part of dreaming. In fact, a lot of it happens during a stage of sleep called slow-wave sleep, which is not during REM sleep, when a lot of dreaming is happening, but it’s a different stage of sleep. And that seems to be a critical time for reactivating recently learned things.
KATIE FEATHER: So what does this all have to do with lucid dreaming? Because it sounds like lucid dreaming is happening at a different stage of sleep than this consolidated memory portion of sleep.
KEN PALLER: Yes, so we understand that deep sleep is very important for memory. REM sleep may also be important for memory, but it’s been very mysterious. It’s been hard to figure out what REM sleep is doing. And there are quite a few different theories, and we need to do more work to try to figure out how REM is important.
And related to that is, is dreaming important for our memory? Does dreaming somehow help our memory function better? Or does it more prepare us for future things that are going to happen? So to study REM sleep, we need to go in there and try to tinker with what’s happening. And so one of our methods of tinkering with brain processing during sleep is to present sounds during sleep that remind people of what they learned earlier.
And we’ve done that in deep sleep over the last 10 years or so. So now what we’ve done is asked, can we do the same thing during REM sleep and during the context of a dream where people are actually observing the information we’re presenting and responding to it, understanding it, and having it even change their dream.
KATIE FEATHER: So it sounds almost like you need to study lucid dreaming as a tool because you need it to communicate with a person in a dream.
KEN PALLER: Yes. Our communicating with people during dreaming is part of the tools we have for trying to understand REM sleep and all phases of sleep.
KATIE FEATHER: So in this study, you were able to communicate with a dreamer who was having a lucid dream. You said it was like trying to come up with a way to communicate with someone on another planet. Describe how you were doing that.
KEN PALLER: So when people are in the midst of a dream, they’re, in a sense, in another reality. They’ve manufactured this reality that they’re wandering around in. And generally that means they’re blocking out information from the outside, which is one thing that we do during sleep is we’re not necessarily attentive to what’s happening in the world around us while we’re sleeping. But we’re not completely inattentive, so some information does get in.
And that’s been known since antiquity, that sometimes a sound from the outside world might change what you’re dreaming about, and you would incorporate that into your sleep. You might hear the dripping of a water faucet and then have some dream about ocean waves and water or something like that. But in our case, we wanted to see if the actual information we present could be understood correctly as it was presented, so the same words being understood.
So we asked questions where we knew what the answer was, such as simple math problems. And people can’t answer in the normal way because during REM sleep, the body is quite paralyzed. Except your eyes aren’t, and so people can move their eyes. That’s why we call it Rapid Eye Movement sleep. The eyes are still moving. So that’s the method we used to have people communicate back to us, by making a signal with their eyes that we then read out and understand whether they had understood our questions correctly.
KATIE FEATHER: Did you go through other possibilities of how to communicate with a sleeping person?
KEN PALLER: Yes. One of our colleagues in Germany used eye movements with people talking in Morse code. So that allowed them to actually speak in sentences, although laboriously. We’ve done other things where you can have people clench their fist in their dream, and we can see a small muscle twitch when that happens. So that’s another method.
And a newer method we’ve been using that we like a lot is sniffing. Because, of course, another thing that works during sleep is respiration. You’re still breathing. And if you breathe through your nostril and just go sniff, sniff, sniff, you can get these three sniffs out, and we can record that with just monitoring the air going out of the nostril.
KATIE FEATHER: So from what I understand about lucid dreaming, some people can do it and some people can’t. But is there a way to practice lucid dreaming if you are someone who can’t always do it?
KEN PALLER: Yeah, that’s an important part of our research, that it’s hard to study lucid dreaming because it’s so rare, and not many people can do it frequently. And even those that do it frequently don’t necessarily do it on the night they might need to do it when they’re in the laboratory for recording. So we use methods to try to provoke lucid dreaming. And that makes it more easy to study this because we can study people that lucid dream a lot, but we can also study people that haven’t lucid dreamed before, and we provoke them into a lucid dream.
KATIE FEATHER: Wow. How did you provoke a lucid dream from someone?
KEN PALLER: So some people learned to lucid dream because perhaps as a child, they suffered from nightmares, and so lucid dreaming could be a strategy for dealing with nightmares. It could allow you to change what’s happening in the dream, or it could allow you to wake up because you realize you don’t want to be in the dream anymore.
So what we do is have them first practice, while they’re awake, a strategy of trying to understand if you’re having a dream at the moment or if you’re awake. And this has been called reality checking. So you can check, is your current reality a dreamed reality, or is it a waking reality? And you have to think about that rather carefully.
So what we do is train people to mindfully consider the present experience and decide whether they’re awake or asleep. And importantly, we do that together with a special sound. So they hear the sound, perhaps the sound of a harp, that cues them to make this check and decide, mindfully, are they awake or asleep. And after practicing that for about 20 minutes before going to sleep, then we let them go to sleep.
And they know, well, if I hear that harp sound, I’m supposed to think about whether I’m sleeping right now. And we’re monitoring their brain activity. And when we see that they’re in REM sleep, we again present that harp sound, very softly so it doesn’t wake them up. And it can seep into their dream and then provoke them to make that check and ideally come to the realization that they’re in the midst of a dream.
KATIE FEATHER: Do you see different brain signals happening in the brains of people who are lucid dreaming versus people who aren’t lucid dreaming?
KEN PALLER: Well, that’s been controversial. There is some evidence that fits with our thinking about brain function, that the frontal lobe is less activated during a non-lucid dream. And the way that fits is that the frontal lobes help you think carefully about what’s happening. And perhaps our ability to– our tendency to just accept what’s happening in a lucid dream is a reflection of the frontal lobe not being completely online and not evaluating the bizarreness of things as carefully as it might otherwise.
And so lucid dreamers perhaps have more of their frontal lobe online and functioning during the course of their dream. There’s some evidence that fits with that. It’s still an ongoing question that’s being investigated.
KATIE FEATHER: I am reminded of the movie Inception, as I’m sure a lot of our listeners will be when it comes to this stuff. How close is all this to what is going on in that movie? Because it seems eerily close.
KEN PALLER: Well, the part that’s not close is that as experimenters, we don’t get to jump into people’s dreams and experience them together. But in another sense, it’s not so hard for us to influence the dream. For example, if a lucid dreamer wants to spend some time solving a particular problem that’s bugging them, it’s very likely they might not remember that goal once they’re in their lucid dream. And so the sounds from the outside can help them guide them to dream about what they prefer to dream about.
KATIE FEATHER: This will be my last question, but can you lucid dream?
KEN PALLER: I’m very interested in it, but I’m not a talented lucid dreamer. I’ve hardly had any lucid dreams. So I’m not speaking from direct experience when I talk about lucid dreaming.
KATIE FEATHER: Well, this was really fascinating. Thank you so much for joining us.
KEN PALLER: Thank you, Katie. It’s been great to talk.
KATIE FEATHER: Dr. Ken Paller is a professor of psychology and director of the Cognitive Neuroscience program at Northwestern University. For Science Friday, I’m Katie Feather.