What Are Dreams?

PBS Airdate: November 24, 2009

NARRATOR: Each night, as we close our eyes and slip away from the waking world, we may enter an even richer one, the elusive realm of dreams.

MALE RESEARCH SUBJECT 1: I was in a kitchen. I remember it had really bright colors and a lot of sunshine, and I saw a bug on the table, and I heard it say, "Hamburger, hamburger."

FEMALE RESEARCH SUBJECT 1: I was riding the subway, and I noticed that I could suddenly see into things. And there was a young woman, and in her purse she had handcuffs.

FEMALE RESEARCH SUBJECT 2: There were two lanes, so it was a normal motorway, apart from the fact that all the cars had no people in them.

MALE RESEARCH SUBJECT 2: I'm holding a big glass of milk, and there's a head of lettuce in it.

ROBERT STICKGOLD (Harvard Medical School) : I don't know anybody who isn't fascinated by dreams. I mean they are outrageous events in our lives.

NARRATOR: They can be bewildering, terrifying, inspiring, but do they mean anything? Are dreams the nonsensical byproduct of a sleeping brain or a window into our unconscious mind, rich with revelations?

PATRICK MCNAMARA (Boston University) : Why would Mother Nature highly activate your brain, paralyze your body, sexually activate you and force you to watch these things we call dreams? Why? Why would Mother Nature do that?

NARRATOR: After more than a century of searching, scientists may finally be nearing an answer, by literally watching dreams unfold and testing their impact on both our sleeping and waking lives.

MATTHEW WILSON (Massachusetts Institute of Technology) : Dreaming is a process, and not only is it useful, it might be essential for making sense of the world.

NARRATOR: Up next on NOVA: What Are Dreams?

FEMALE RESEARCH SUBJECT 3: I was walking down this really bizarre hallway, and every time I would open a door, there would just be this blinding light.

MALE RESEARCH SUBJECT 3: So I take off and fly. And I'm starting to accelerate faster, faster, faster, and I realize I was an electron inside an R.C.A. circuit, moving around at the speed of light.

MALE RESEARCH SUBJECT 4: It's dark outside; kind of raining; very, very scary; ominous. And all the water puddles, if you touch them, you catch on fire.

FEMALE RESEARCH SUBJECT 4: She was very overweight and actually was growing a real beard.

NARRATOR: They're eerie, impossible and often, just plain weird. Yet some say they've changed the world.

DEIRDRE BARRETT (Harvard Medical School) : Dreams have been responsible for two Nobel prizes, the invention of a couple of major drugs, and innumerable novels, films and works of visual art.

NARRATOR: Usually they fly through the mind unremembered. Yet they may be key to understanding the mind itself.

PATRICK MCNAMARA: If you want to understand human nature, the hum0an mind, what makes us tick, you need to look at dreams.

NARRATOR: The scientist most associated with dreams is still Sigmund Freud, who saw them as brimming with symbols, mostly sexual. Such symbols took form as the sleeping brain tried to disguise forbidden urges welling up from its unconscious, though even Freud cautioned that this kind of thinking could be taken too far.

HOWARD KATZ (Boston Psychoanalytic Institute) : At some point, he said you can be too literal. You can say every single thing is standing for something sexual. And you know, sometimes a cigar is just a cigar.

NARRATOR: Today, advances in brain science have inspired new theories about dreams, building on a discovery made years after Freud's death, when science finally got a look at the sleeping brain.

The breakthrough came in 1953, when Nathaniel Kleitman and Eugene Aserinsky began recording people's brainwaves as they slept through the night.

ROBERT STICKGOLD: They put electrodes onto the head that could pick up the electrical activity of the brain underneath. And they had known when people are awake, that signal looks very fast and not too interesting—it looks almost like noise—but that when people fall asleep, that you would sometimes have the brain activity start to go up and down in a slow pattern, and you could then tell whether someone was awake or asleep; or so they thought.

NARRATOR: The researchers had assumed sleeping brains were resting brains. But every 90 minutes or so, as their subjects slumbered, something odd happened.

ROBERT STICKGOLD: Their eyes were closed, their head had drooped; they didn't answer when you called them by name. They were clearly asleep but the electrical activity of the brain said they were awake.

NARRATOR: And it wasn't just their brainwaves that seemed strange. They were sexually aroused. Their heart rates and breathing had become irregular. Their eyes darted about beneath shut lids.

It was these eye movements that gave the state its name: Rapid Eye Movement, or REM sleep.

But what was REM sleep for? The answer seemed to come from the sleepers themselves.

PATRICK MCNAMARA: During REM sleep, what the researchers invariably found, when they woke up a subject, was the subject would report, "Hey I'm dreaming, and I just had a vivid dream."

NARRATOR: So was REM sleep dream sleep? The idea seemed more than plausible when you considered REM's most dramatic characteristic.

ROBERT STICKGOLD: Another feature of REM sleep is that your muscle tone just goes absolutely down to zero. You become functionally paralyzed. If you're sitting up in a chair watching TV, you know, and the head nods and falls and you fall asleep, that's not REM sleep. If you fall into REM sleep, you would literally roll off the chair onto the floor, because your body becomes absolutely relaxed, almost paralyzed, in the sense that you can't make your muscles actually work. And it becomes absolutely calm and non-responsive.

NARRATOR: Nature, it appeared, had devised a special state of paralysis to house our dreams, one in which they remained internal experiences. It was a conclusion that seemed impossible to deny, when researchers learned to switch the paralysis off.

This cat looks as if it's awake; in fact, it's deep in REM sleep.

This dog appears to be running; it too is in REM sleep, and, like the cat, dreaming.

To see these dreams played out, scientists disabled the part of the brain that paralyzes muscles during REM sleep.

PATRICK MCNAMARA: And what we see when you do this, with cats in particular, is that they can walk around during REM sleep, and their behavior is not random, it's not chaotic. They're not just doing any old crazy thing. They appear to be doing the kinds of behaviors that cats like to do, like stalk a prey, you know, play with a mouse or something. So presumably that's what they dream about when they go into REM sleep, so that's what we think is happening.

NARRATOR: But what about people? Could human dreams be watched as well? Performing surgical experiments on human subjects was, of course, unthinkable, but the discovery of a new brain disease also made it unnecessary.

TINA CURSLEY (Wife of Research Subject) : Well, it was me, telling him he's got to go to the doctor's and sort this out, because I'd have to jump out of bed quick.

NARRATOR: Tom Cursley has a condition known as REM sleep disorder. It prevents the paralysis of REM sleep, so he acts out his dreams.

TOM CURSLEY (Research Subject) : I can picture, now, being in this field, a river in the background, and I don't know, about a dozen cows grazing the grass, and they slowly start coming towards me and nudging me and push me out of the way.

TINA CURSLEY: He's shouting and raging about everywhere. The bedside cabinet went over the other night, and he didn't even know he'd knocked that over.

NARRATOR: Dr John Shneerson is an expert on this condition.

JOHN SHNEERSON (Papworth Hospital, Cambridge, England) : It's absolutely classical for the REM sleep behavior disorder. It's just what happens. It starts off with movements that the partner thinks is a bit unusual but nothing special, just kicking and just a bad dream, but it becomes more frequent, more intense and it can be dangerous for the partner and dangerous for the dreamer. In fact a lot of people with this condition end up with nothing in the bedroom at all. They take out all the bedside tables, all the lamps, all the sharp corners, which might injure themselves. They end up almost in a padded cell.

NARRATOR: Not all sufferers have nightmares. Here, a sleeper puffs on his finger monitor, dreaming it's a cigarette.

JOHN SHNEERSON: Another patient was dreaming that there were animals coming in the room, and when he woke up he was on the mantelpiece and found it difficult to get off there. In fact, he didn't know how he got up there. He must have been very agile to get up there, very motivated to get that far.

NARRATOR: REM sleep disorder seemed to suggest that dreams were important. Why else would nature go to such lengths to let most of us dream safely?

Such a conclusion might have seemed obvious, but by the late '70s, a new theory was roiling psychology. It came from Harvard researchers Alan Hobson and Robert McCarley.

G. WILLIAM DOMHOFF (University of California, Santa Cruz) : And it stressed the fact that there's a particular part of our brainstem that triggers REM sleep, sending up signals to the higher parts of the brain that were kind of random and chaotic.

NARRATOR: Dreams, the researchers argued, were more physiological than psychological: the result of our higher brain doing the best it could to make sense of meaningless neural impulses.

G. WILLIAM DOMHOFF: Now that led them to say that dreams have some psychological coherence, some pattern, but they have no purpose. And certainly not the psychological purpose that Freud claimed for them.

NARRATOR: So are dreams basically gibberish, or, as Freud maintained, a doorway to the unconscious or something else entirely?

For the debate to move forward, scientists would have to make yet another key discovery.

As most other people are heading home, Erica Harris is arriving for work at Boston University. This is when dream researchers frequently start their day.

ERICA HARRIS (Boston University) : The experiment tonight probably won't end 'til about 6:30 or 7:00 in the morning, when we're finally done. It's very tiring, but we enjoy our work, so we're looking forward to it.

NARRATOR: Also arriving is her guinea pig, Ross, a 19-year-old student who has come here for a bad night's sleep.

TECHNICIAN: Hello.

ROSS (Sleep Study Subject): Oh, hi. I'm Ross.

TECHNICIAN: Hi, Ross.

NARRATOR: Over the next eight hours, they will focus on an aspect of dreams only recently discovered.

ROSS: Hi.

ERICA HARRIS: We're so glad you could make it tonight.

This is to measure any different type of muscle movement that he might have at his eyes or at his chin.

We need to measure the brainwaves, because the brainwaves show us a different picture. They look different depending on the different type of sleep that the person goes in.

NARRATOR: With this much wiring, it's unlikely a brainwave will go unnoticed.

ERICA HARRIS: There are 26 different electrodes that Ross will have on tonight. We're going to have a pretty good idea about everything that's going on with him while he's sleeping.

NARRATOR: But even with all this technology, there is still only one way to find out if Ross is dreaming.

ERICA HARRIS: Sweet dreams.

NARRATOR: Project leader Patrick McNamara explains the challenge.

PATRICK MCNAMARA: There is no technology that allows us to know a hundred percent certainty that a person is dreaming. You can see the full panoply of characteristics that occur during REM sleep, you know: the paralysis, the eyes darting back and forth. You can put him under a neuroimaging scanner. You can see the areas of the brain that light up during REM sleep light up, and you can expect them to report a dream when you wake them up, but they may not. Unfortunately, the best way to find out if a person is dreaming is to wake them up and ask them.

NARRATOR: Despite this limitation, the experiment will probe a surprise discovery of the recent past: sleep studies have revealed that not only do we dream in REM sleep but during non-REM sleep, as well. And these two dream states may be fundamentally different, affecting us in different ways.

PATRICK MCNAMARA: So this should tell us something crucial about the nature of the mind, because if you want to understand what makes us tick, you need to look at dreams.

NARRATOR: It's now 11:00, and Ross has nodded off, which means his brain has begun to cycle through the five stages of sleep.

We start out with non-REM sleep, beginning with stage 1, light sleep. As we pass into deep sleep, stages 3 and 4, our brainwaves grow increasingly long and slow. Then we begin a return journey, but don't quite make it. Just short of waking comes REM sleep, after which we repeat the cycle, four or five times in a night.

ERICA HARRIS: On this monitor, we are looking for him to descend into the various stages of sleep, so we want him to make his complete sleep cycle prior to us awakening him.

NARRATOR: Ross has completed one sleep cycle, which lasts about 90 minutes.

Soon he is entering again into non-REM sleep.

ERICA HARRIS: Right now, what we can see is that he's in non-REM sleep. And we know that because we see the shape of the brainwaves where they're very close together, like this, and then we see some that are very spiky. This is the beginning of the transition to the stage in which we want to wake Ross up.

TECHNICIAN: Ross, wake up, it's time to do your packet.

NARRATOR: After awakening from non-REM sleep, Ross does indeed report having a dream.

ROSS: I was with people I knew, no real friends, in specific, but I was with people I knew, and we were trying to find somewhere.

NARRATOR: It is not just that we dream in non-REM sleep. As the experiment will reveal, these dreams are different from REM dreams.

ERICA HARRIS: So the first thing that he's working on right now is a mood questionnaire, and basically he might see three letters like O, P, T, and he's supposed to complete some kind of word for that.

NARRATOR: The words Ross chooses will reveal how he's feeling about himself after non-REM dreaming. His answers reflect positive emotions.

PATRICK MCNAMARA: We found, in our experiment, there was a very reliable difference in self-concept, self-regard, and there was an increase in positive regard of the self after awakenings from non-REM.

NARRATOR: Ross goes back to sleep. The next time he's awakened he will be well into REM sleep.

Five a.m.

TECHNICIAN: Ross, time to wake up.

NARRATOR: This time Ross comes up with one negative word after another. McNamara speculates that this shift in mood, detected after Ross's REM dream, can be traced to an ancient structure, the amygdala, found in each hemisphere of our brain.

PATRICK MCNAMARA: I think that we have more negative emotions during REM-related dreams because during REM sleep the amygdala is very highly activated, and the amygdala specializes in handling unpleasant emotions like intense fear or intense anger or aggression.

NARRATOR: Finally the night is over, but the experiment has more to reveal. McNamara is beginning to connect the proportion of REM and non-REM dreams with our mental wellbeing.

It could be a factor in depression.

PATRICK MCNAMARA: Normally, we fall asleep through non-REM sleep, but depressives, people with endogenous depressant depression or severe depression, they go right to REM, and then they stay in REM, and they spend too much time in REM. So if REM sleep is associated with all this unpleasant emotion and you get too much REM, then you are going to have a lot of unpleasant emotion. We call that depression.

NARRATOR: At Harvard, meanwhile, Robert Stickgold is focusing on the dreams of non-REM sleep. He, too, recruits human subjects to sleep over in his lab, but first they get an assignment.

ROBERT STICKGOLD: So John, here, is mostly just having a lot of fun. He's learning how to play this game, Alpine Racer 2, which is a downhill skiing simulator.

He actually controls that character on the screen by moving his feet, and he's learning a lot about how to do it. And what we think is that as the brain goes to sleep, it's going to come back to these images.

JOHN (Sleep Study Subject) : It's intense. I'm trying to beat a time, and I'm trying to stay in between these gates, and it's difficult, but it's a lot of fun.

NARRATOR: That night, John is awakened repeatedly during non-REM sleep and asked about his dreams. Early on, they're simple re-enactments of the ski game. But as the night passes, they begin to incorporate other memories.

NURSE: Please report now.

JOHN: I was walking through boot prints in the snow—already-made boot prints—like, copying them, going into the ones, stepping into the ones that were already stepped in, like following somebody else's steps along in the snow.

ROBERT STICKGOLD: What he's dreaming about is how much easier it is to walk through the snow, if you go exactly where you stepped last time. I can just imagine the brain trying to say, "Does what I know about walking in snow help me think about skiing on snow?"

NARRATOR: Such a dream, Stickgold believes, does far more than while away the night.

ROBERT STICKGOLD: And I think this is all about the function of sleep and the role of dreaming in processing memories, that it refines the memory, it improves the memory, it makes the memory more useful for the future, and so when they come back, they're going to be better.

NARRATOR: And John is better. The next day on the virtual slopes, his performance has clearly improved.

JOHN: I was kind of hitting the wall, coming up on this part, but I'll see if I can avoid it. Yeah, that's pretty good.

ROBERT STICKGOLD: We know that they are getting better when they play again. And in other studies we have evidence that when they dream about it, those people who dream about it actually end up performing better the next time.

NARRATOR: If non-REM dreams help us learn, then what about the dreams of REM sleep? What do they accomplish? And how might the two kinds of dreaming work together?

At M.I.T., a scientist who eavesdrops on the dreams of rats may be nearing an answer.

By placing electrodes in a rat's brain, Matt Wilson can read its mind, seeing exactly how its brain cells, or neurons, fire, as it experiences its world, in this case a maze.

MATT WILSON: Individual neurons will respond based upon what the animal is doing, where it is in the maze. So wherever the animal is, we see unique patterns of brain activity.

NARRATOR: Each of these patterns corresponds to a specific place in the maze explored by the rat. But, remarkable as it is to look in on a rodent's inner life, the big payoff comes later. As the rat sleeps, the patterns recur, seen here as flashes of color superimposed on the maze.

MATT WILSON: So the animal is asleep. It's not moving. It's not interacting with the world. And yet we see a lot of structured activity going on in the brain. And when we look in detail at that activity, we see that these patterns are direct reflections of patterns that we had seen when the animal was awake.

NARRATOR: Wilson is convinced he has found a way to watch a rat dream and know what it's dreaming about; in this instance, running a maze.

MATT WILSON: And I think that was really the moment of great insight. Not simply that there was dreaming going on, but that we had access to this.

NARRATOR: Like humans, rats have two distinct dream types, and Wilson is homing in on their differences. During non-REM sleep their dreams play out as brief bursts of neural activity, which mirrors past experience compressed into seconds.

MATT WILSON: Now, when we get to REM sleep, now things change dramatically. Memories are replayed, but they are not compressed, they're not accelerated, they don't occur in these small fragments. They are played out as though the animal were actually experiencing moving through a world, but that world is being generated from the inside.

NARRATOR: In fact, REM dreams can be five times longer than non-REM dreams. And in human beings, at least, they are anything but a simple replay of the past.

MATT WILSON: So the speculation is that during non-REM sleep, the brain is taking the past and trying to figure out how that might relate to the future, and in REM, actually trying to experience the future, move into the future.

NARRATOR: The dreams of REM, in other words, may be simulations, which allow us to face challenges and test possibilities.

ROBERT STICKGOLD: My sense is that when we're asleep and when we're dreaming, we are actually conscious and figuring out what's important about what happened to us and how that relates to everything else that's happened to us in the past and figuring out what that means about our future.

MATT WILSON: And when you think about the challenge that animals, that we as humans and the brain in general faces, it is the unknown of the future. And in REM, we may have the opportunity to step into that future world with no risk, because the consequences are simply things don't work out as you might have expected, and then you wake up.

So these states may be what are essential for allowing us, as individuals, to reach our maximal level of potential.

NARRATOR: When dreams begin testing scenarios, the results often seem ludicrous.

MALE RESEARCH SUBJECT 1: I was in a kitchen. I remember it had really bright colors and a lot of sunshine, and I saw a bug on the table, and I heard it say, "Hamburger, hamburger."

FEMALE RESEARCH SUBJECT 1: I was in a field, and I could see what looked like hundreds of silver and purple flowers. And as I approached I realized that they were actually parasols, and then they would make a sound like a gong.

NARRATOR: But as preposterous as some dreams seem, a few may have changed the world.

DEIRDRE BARRETT: Dreams have been responsible for two Nobel prizes, the invention of a couple of major drugs, other scientific discoveries, several important political events, and innumerable novels, films and works of visual art, so they've been very important in our society.

NARRATOR: Deirdre Barrett of Harvard explores the power of dreams to give us insights we might never otherwise have.

DEIRDRE BARRETT: We can see things much more clearly when we think about them in dreams, and it also helps us think outside the box. Our associations are looser and more intuitive and less linear.

NARRATOR: The classic symbol of science, the periodic table of the elements, is said to have come to the Russian chemist Dmitri Mendeleev during a dream. In 1844, American inventor Elias Howe was trying to design his first sewing machine, but he couldn't work out how to make it hold the needle. One night he dreamed of being attacked by cannibals with spears.

DEIRDRE BARRETT: And as he woke up in terror, the last thing he saw was that all of their spears had the hole at the pointed tip of the spear, and he realized that's where you put the hole in a sewing machine needle.

NARRATOR: And the story goes that Dr. Frankenstein and his monster were dreamed up by Mary Shelley.

Or were they? Not everyone agrees.

G. WILLIAM DOMHOFF: Many of the claims about great discoveries during dreams are very hard to document. But what we always have to remember is these people were intensely thinking about these issues. So there may have been some discoveries based on reflecting on dreams, but that is waking consciousness, reflecting on the dream.

NARRATOR: But even if famous creators achieved their breakthroughs after waking, dreams can still claim some of the credit, according to sleep researcher Sara Mednick.

SARA MEDNICK (University of California, San Diego) : What stage do you think this is?

RESEARCHER: Looks like stage 2, actually.

SARA MEDNICK: Right, because there are sleep spindles.

NARRATOR: In a recent experiment, she recruited volunteers to play a series of word games that demand creative leaps.

SARA MEDNICK: We define creativity as putting together disparate ideas in new and useful combinations. So what we have is three different words. And we have people trying to find a fourth word that goes with those words. And so what they have to do is find a new connection that's not their direct associate, but a more remote associate.

NARRATOR: Before playing, volunteers, like Tristan, are shown examples.

RESEARCHER: Try these next two: surprise, line, birthday.

TRISTAN (Sleep Study Subject) : Um, present?

RESEARCHER: No, very close. The answer is "party." So: surprise party, party line, birthday party.

NARRATOR: After the game, Tristan's next assignment is to nap. Mednick monitors his sleep cycles and eye movements. Sixty minutes later, he appears to be entering REM sleep.

SARA MEDNICK: So, here, we have a lot of rapid eye movements. You can see this is indicating he's probably having a dream right now.

NARRATOR: Only a third of the volunteers take naps like these. The others either rest quietly or are awakened before entering REM sleep. Then everyone plays a new word game.

SARA MEDNICK: I was looking for a REM result for creativity. I definitely thought we'd be able to find it. I was surprised by the magnitude.

NARRATOR: Those who had REM sleep scored 40 percent higher. But quiet rest or non-REM sleep produced no benefit whatsoever.

SARA MEDNICK: The reason why we think that REM sleep helps you with creativity is because REM sleep is a very active time in your brain. Sometimes your brain can even be more active than during waking. And you actually have these different areas of the brain that are speaking to each other. So it's actually able to start to free associate amongst its own ideas and memories.

NARRATOR: Clearly REM sleep can boost creativity, but do REM dreams have anything to do with it?

SARA MEDNICK: The dreams that we have during REM sleep, they're very wild. They're very fanciful. They're clearly the brain having a period of loose associations, where you are able to put connections together, between new and old ideas, finding new solutions to new problems.

NARRATOR: This ability to harness the creative power of dreams is not just the preserve of genius. It seems that with a little REM sleep, many of us can also do it.

DEIRDRE BARRETT: Just say to one's self, "I want to dream about X tonight," as you're drifting off to sleep, and in my research I find that about 50 percent of people can do that, if they just practice that for a brief period of time. And about half will get an answer that is really gratifying to whatever the issue is.

NARRATOR: Of course, sometimes we get the dreams we least hope for. But these may be the most valuable ones of all.

MALE RESEARCH SUBJECT 4: It's dark outside; kind of raining; very, very scary; ominous. There's, like, this kind of spaceship...

DEIRDRE BARRETT: And I saw the chain on my arm. With these huge chains was this big stone tablet, all inscribed with hieroglyphics.

FEMALE RESEARCH SUBJECT 5: Suddenly I jump off the bed. I want to run into my parent's bedroom. There's a long hallway I have to go through to get there. And then, just at that moment, this hand and arm and body reaches for me; this is the giant made of shadows.

NARRATOR: No doubt, such episodes are terrifying. But could it be we need them? Antti Revonsuo is convinced of it.

He's a Finnish scientist who collects nightmares. He has concluded that many of the bad dreams we have today are the same as those experienced by our ancient ancestors.

ANTII REVONSUO (University of Turku) : Well, it's pretty certain that our ancestors did dream, because dreaming seems to be biologically programmed into our brain, and the brain that our ancestors had was pretty much identical with our brain. And we know that our ancestors lived in an environment which was full of all sorts of fatal dangers.

NARRATOR: The same dangers, Revonsuo says, often show up in nightmares today, particularly in those of children.

FEMALE RESEARCH SUBJECT 2: There was one wolf. And he started chasing me, and I ran and ran and ran. And afterwards he, he stopped for a minute and barked, and then another wolf came and another and another and another. And then, in the end, there was a whole pack of wolves with big long teeth, and they were very, very hairy and big and scary, and they started chasing me.

NARRATOR: According to Revonsuo, our ancestors had such dreams, and bequeathed them to us, because they were indispensable rehearsals in the struggle to survive.

ANTII REVONSUO: The nature of bad dreams and nightmares is that they contain threatening events and they force us to go through those simulated threatening events in order that in the waking world we encounter similar or different kinds of threatening events, and then we are more prepared to survive those when we have been training for them in our dreams.

NARRATOR: Revonsuo believes this mechanism for rehearsing stressful events stays with us for all our lives, but as we grow up, dreams about wild animals are replaced by modern horrors.

FEMALE RESEARCH SUBJECT 6: I was dreaming that I couldn't find the class, and then my friend had to come to this class, and I couldn't find her, either, and she couldn't find me. And on my way to the class, I opened the door of the elevator, and I hit a little girl, and she died.

ANTII REVONSUO: Adults have very modern types of nightmares and bad dreams, like losing your wallet, crashing you car or something like that. So it seems our brain is capable of adjusting itself and including more modern threats.

NARRATOR: According to Revonsuo, we should be thankful for these fearsome visions, which may exist to help us survive.

ANTII REVONSUO: Bad dreams and nightmares are a good thing. They force us to be prepared for similar events in the waking world. Without nightmares and bad dreams, there is a good chance that humanity wouldn't be here.

NARRATOR: But if dreams are so important to our waking lives, what if one day they just stopped? Would we lose our capacity to learn, prepare, anticipate?

Could such a thing happen? According to this man it does.

MARK SOLMS (University of Cape Town) : I frequently found when I ask patients after they had sustained strokes, for example, whether they are dreaming or not, initially they're not entirely sure. And then it's in the following days—because they are now paying attention to their dreams—that they report to me with increasing confidence that they are no longer dreaming.

NARRATOR: True, many of us say we don't dream, when in fact we just can't remember doing it. But Mark Solms is convinced that the rare individuals he studies really have nothing to remember.

One of these is Heather Jones, who lost her dreams three years ago, after a stroke.

HEATHER JONES (Research Subject) : Before my stroke I definitely was somebody that had lots of dreams.

After my stroke it was just, literally, going to sleep was like going into a blankness. It's almost as if you're just absent for a while. There was just not that same sense in the sleep or when I was waking up that I'd been dreaming. There was no memory of dreams and no sense of having been dreaming.

NARRATOR: But it was damage to a part of Heather's brain, the parietal lobe, which convinced Solms she really wasn't dreaming.

MARK SOLMS: ...parietal damage, like Heather sustained, frequently stop dreaming completely in the early stages, after the onset of the damage. That's because the parietal lobe serves the purpose of combining our different senses. Hearing and vision and touch all come together there. And the imaginary space that we are living in during our dreams is generated in that part of the brain. So if it's damaged you can't dream.

NARRATOR: So does going dreamless have consequences? Apparently, though they don't seem particularly dire.

HEATHER JONES: I could go to sleep very easily. I wasn't having what I would call good quality sleep at night, probably waking several times through the night. So I wasn't getting a continued sort of period of sleep.

When I woke up, I just felt tired still.

MARK SOLMS: The relationship between sleep and loss of dreaming is in fact something that I'm busy researching at the moment. Our preliminary findings suggest that at least non-dreaming patients fall asleep perfectly easily, but then they keep on waking up throughout the night, in fact, particularly during REM sleep. It's almost as if when, when you might have expected that they would be dreaming, they wake up.

NARRATOR: Decades after the discovery of REM sleep, scientists are beginning to understand how dreams affect our lives.

But they are also grappling with another intriguing question. Do dreams mean anything?

DEIRDRE BARRETT: I descended from the sky onto this sort of beautiful fairy tale planet.

FEMALE RESEARCH SUBJECT 7: I had a flat cardboard box, you know, those ones that you assemble together. And I took it up to this pyramid, and it had a severe drop at one end, and I put it together. And then I jumped down off the pyramid in the box and hit the pavement. But the strange thing was it didn't actually hurt.

FEMALE RESEARCH SUBJECT 8: I was playing in my room with my sister, and then I was about to go outside, and my mum said, "Keep your head up, because there's a witch about."

ROBERT STICKGOLD: My interest in dreaming as a scientist is, "Boy, I just want to understand these things." It's just so interesting and so exciting.

MARK SOLMS: People intuitively know that there is something about their dreams that is meaningful. People are endlessly fascinated by dreams.

NARRATOR: The belief that dreams mean something remains central to many cultures. Deep in the forests of Northern Canada live the Atikamekw people. Interpreting their dreams is part of the tribe's daily life. Each morning, members of the community gather in dream circles like this one. The dreamers speak; the elders draw on folklore to interpret what they hear.

PAULINE (Atikamekw Community Member) : In my dream, I saw the river, and it was flooding. It rose and rose. And I saw my son up high.

NARRATOR: One elder who practices dream interpretation is Marianne.

MARIANNE (Atikamekw Elder) : Rising water represents sickness; a soul is sick.

NARRATOR: Pauline acknowledges her son's drug addiction, and then describes a second dream.

PAULINE: Later, I dreamed the water had receded. I saw my son again at the low water level. He was waving goodbye. I screamed, "Ivan!"

MARIANNE: The low water level means that Ivan's drug addiction will soon be cured.

NARRATOR: For cultures like the Atikamekw, it is beyond question that dreams have significance. But do they? Can science find meaning in dreams?

In Montreal, one psychologist is using statistics, not folklore, to tell us what dreams mean.

ANTONIO ZADRA (University of Montreal) : There is convincing evidence that leads us to believe that the content of dreams tell us a lot about how the brain can process information and is important for our psychological wellbeing.

NARRATOR: Antonio Zadra is a scientist in the University of Montreal's dream lab. Here, he has collected over 6,000 REM and non-REM dreams, breaking down each one into its basic elements, and turning each element into a number.

ANTONIO ZADRA: Well, what we did is we coded the entire dream series in terms of various elements. Who are the characters, the emotions, the settings, things of that nature? And then we entered these quantifications, these resulting numbers in our spreadsheet.

NARRATOR: The result of this painstaking work is a comprehensive database of our dream lives. Zadra can tell us how often we dream about sex and whether this involves our partner or a celebrity. He can even tell us how often we have unpleasant dreams. But his database is most revealing when telling us about the dreams of an individual.

ANTONIO ZADRA: What we want to see is a whole series of dreams so that we can then detect patterns that recur over that entire dream series and thus get a better idea of what this person's dream life is generally like.

NARRATOR: Comparing someone's dream elements with the norm tells Zadra what they may mean.

This is a series of dreams from a 48-year-old professional man. He calls his wife "B."

ANTONIO ZADRA: "B and I are making breakfast. I was also brewing some coffee, but when I looked over at the coffee maker it was..."

NARRATOR: "It was overflowing. There was coffee all over the counter and coffee just kept pouring out."

ANTONIO ZADRA: "B was yelling, 'What did you do, what did you do?' I tried unplugging it."

NARRATOR: "I removed the glass container, but it wouldn't stop."

ANTONIO ZADRA: His mother arrives; he's unconsolable, and parents, too.

NARRATOR: "But my mother keeps telling people it's all my fault. It's loud and I try to defend myself. I wake up."

From this series of dreams Zadra spots unhappiness as a recurring theme.

ANTONIO ZADRA: "When I tried to move the car the wheels just kept spinning."

NARRATOR: "B was getting very upset and was telling me there was still too much snow. I got out again and everything seemed okay."

ANTONIO ZADRA: "I got back in, but nothing happened, just more spinning."

NARRATOR: In fact 80 percent of this man's dreams include unhappy events. Yet Zadra's research reveals that the average occurrence of misfortune in the dreams of middle-aged men is only 34 percent.

ANTONIO ZADRA: The other thing that really stands out with his dream series is that almost all of the other dream characters in his dreams are women—there's an, almost an absence of male figures—and the interactions he has with these women is almost invariably negative.

NARRATOR: Again, the frequency of these negative dreams is abnormally high.

ANTONIO ZADRA: If I were to make an educated guess about what is going on in this particular man's life, is that there seems to be concerns about relationship issues, and also he is definitely overwhelmed by factors which are impacting him negatively but which he feels he has no control over.

NARRATOR: So it came as no surprise to Zadra to learn that five years later the man divorced.

Zadra has worked out the norm for many dream events. Only 20 percent of women's dreams about sex, for example, involve their partners, but dreaming men are worse, coupling faithfully just one out of seven times. Thirty-three percent of our dreams involve unhappy events. And while some dreams are outlandish, most are more a reflection of our waking concerns.

ANTONIO ZADRA: Dreams are relatively transparent. And I think there is good evidence to suggest that dreams tend to reflect people's emotional concerns and also things that preoccupy them in their social lives.

NARRATOR: Preoccupations that we seem to be trying to work out as we sleep.

ROBERT STICKGOLD: What's amazing is it looks like those processes of extracting what's important, integrating it with our other memories and projecting it into our future, those critical, brilliant functions of the human mind and the human brain might actually occur, not while we're awake, not while we're trying to figure it out consciously and intentionally, but, instead, while we're asleep and while we're dreaming.

NARRATOR: So what is science telling us about our dreams? That they're a crucial tool which helps us learn; a key to creativity, even survival; a window onto our secret selves?

Throughout the long night, our mind seems to be preparing us to face the coming day.

ANTII REVONSUO: The important thing is just to go through the training, and then we get all the training benefits, even if during wakefulness we have no idea we've been training all night.

DEIRDRE BARRETT: I think that their value lies in what a different mode of thought they are. They're so much more intuitive and visual a mode of thinking, and in our culture we spend so much time in this very logical linear mode of thinking that their main benefit lies in presenting such a different point of view.

ROBERT STICKGOLD: Our brain is working on figuring out the importance and significance of events from our days, how they fit together with old events in our past, what they mean about likely events in the future.

G. WILLIAM DOMHOFF: And we don't know whether it's going to be fun, whether it's going to be scary, whether it's going to be poignant. It's a whole new adventure, every time.

NARRATOR: So the next time you enter the elusive world of dreams, know that your brain may have good reason to send you on these adventures of the night.