It was my dentist who first suggested I might be a bit stressed. My teeth showed signs of grinding and clenching while I slept. If it continued, he told me, I could wind up with a cracked tooth and an appointment for a root canal. So a few weeks later, I had a mouth guard to wear through the night. It didn’t do much for my stress, but at least it protected my teeth.
However, I quickly discovered that I’d swapped one problem for another. I now have a recurring dream where my teeth shatter and fall out of my jaw. I’m pretty sure that my night guard is the culprit. The dream started after I began wearing it, and, whenever I wake up from the dream, I find myself gnawing on the hard plastic guard. Sweet dreams these were not.
But as someone who studies the brain, at least I had something new to be curious about. I started to wonder about the link between physical sensations and what happens in our dreams. Luckily for me, Alfred Maury had a similar question.
Maury, a dream scientist in the nineteenth century, was one of the earliest to investigate how humans incorporate physical sensations into our dreams. Using himself as the research subject, he would have an assistant create different physical sensations while he slept, like dropping water on his forehead or holding a burning match under his nose. He found that these sensations were often incorporated into his dreams. In one instance, Maury dreamed about a ship’s gunpowder exploding when he smelled a burning match. He concluded (and my own experience with my mouth guard confirms) that our senses don’t shut off when we’re asleep. The brain continues to receive sensory information, and those sensations worm their way into our dreams.
I learned about Maury’s work from dream researchers Robert Stickgold and Antonio Zadra. Their new book, When Brains Dream, explores the history, science, and purpose of dreaming. Stickgold and Zadra have studied dreams since the 1990s, and their book draws on this expertise to bring a scientific lens to dream research. For those worried that a scientific approach might diminish the magic of dreams, don’t worry. For Stickgola and Zadra, this newfound knowledge “doesn’t take away the mysterious sense of wonder that our dreams create; it magnifies it.”
I had the chance to connect over Zoom with Stickgold, a professor at Harvard Medical School and director of the Center for Sleep and Cognition, for a conversation about his new book and the science of dreaming. We discussed other early pioneers of dream research, how dreams vary between sleep stages, what lucid dreaming is, and the powerful, yet potentially dangerous, methods behind dream hacking.
Our conversation has been edited for length and clarity.
Caitlyn Finton: Your book is titled When Brains Dream, but you actually spend a bit of time exploring the basic biology behind sleep. Why is it important to know about sleep in order to understand dreams? How do those two impact each other?
Robert Stickgold: Dreams occur in a very specific brain state, or collection of brain states, which we enter when we’re asleep. Arguably, the reason that sleep evolved was to give organisms a chance to go into these altered brain states where memory processing can occur differently.
In REM [rapid eye movement] sleep, we’ve got serotonin and norepinephrine release completely shut off in the brain, which dramatically alters the sort of the programming that’s running the brain. The outflow from the hippocampus is pretty much shut off in REM sleep, which blocks our ability to reactivate recent episodic memories. In REM sleep, the dorsolateral prefrontal cortex is shut down almost completely, which means that the brain loses its capacities for executive control, logical reasoning, and impulse control. And the brain ramps up the midline limbic system, so we tend to be hyperemotional.
Arguably, the reason that sleep evolved was to give organisms a chance to go into altered brain states where memory processing can occur differently.
All of those are in the service, I would argue, of allowing a certain type of memory processing to occur while we’re asleep that we simply cannot do when we’re awake.
So in your view, dreaming has a very specific function, and we can only get to that function while we’re in sleep.
We can only reliably get to that function when we’re in sleep. Whether we can get close to it with meditation, mind wandering, recreational or experimental drugs during waking, those are kind of open questions. But certainly evolutionarily, the function of sleep is to get to this altered state where dreaming occurs.
You and Antonio begin the book talking about the history of dream research. I was intrigued to find out that it didn’t start with Freud. Can you briefly talk about what some of the dream research pioneers were studying before Freud and how their work shaped dream research?
I think anybody who’s in public relations now should be in awe of Freud, because he did an awesome job of convincing the entire world that nothing interesting in dream research happened before him. He has this introductory chapter in his book The Interpretation of Dreams where he talks about many of these prior researchers, and he basically said, You know, they didn’t really show us anything of interest or find anything interesting. But in fact, they proposed almost everything that Freud proposes.
For example, there’s Marie Jean Léon, Marquis d’Hervey de Saint Denys. He did these wonderful experiments where he traveled around France in the mid 1800s, 50 years before Freud. Whenever he went to a new town or city, he would buy a perfume and spray himself, one in each city. Then back home in Paris, on various nights he would have his servant come in and spray him with one of the perfumes and he would settle back [to sleep] for five or ten minutes. The servant would then wake him up and collect a dream report. And it would be not uncommon for him to dream about being back in the place where he had experienced [the perfume].
He was able to show, first of all, that odors can get into the brain when you’re sleeping, they can be processed, and they can be tracked to associative networks to find, for example, this odor goes with this location, and then he could have a dream about it. He was also able to combine two perfumes and get sort of a meld of two locations. So he was able to show all of these abilities of the brain to do associative processing. A lot of the things that Freud put forward, including things like different stimuli being combined into one condensation or distortion, these were all hypothesized ahead of time by other people.
I had always heard that we only dream in REM sleep, and I was really surprised to find out that we dream in other sleep stages as well. How do our dreams differ between the sleep stages?
That myth came from scientific research and scientific articles written in the 1950s when REM sleep was first discovered. They collected dreams from REM and non-REM sleep, and they set this very strict criteria for what constitutes a dream, in terms of its complexity, its length, and its emotionality. When you set high enough standards for what constitutes a dream, most of it does come from REM sleep. But if you ask about conscious mental experiences during sleep and say that’s what we mean by a dream, we see it in all stages of sleep.
In the sleep onset period, the first two or three or four minutes, you get reports of mentation [mental activity] that’s 80 percent of [the mentation found when you’re] awake, as good or better than you do in REM sleep. REM sleep tends to be 75 to 80 percent. In stage two non-REM, which makes up 60 percent of the night, we get report rates of 50 or 60 percent. And in slow wave sleep, the deepest stages of sleep, it drops down to 30 or 40 percent.
When you set high enough standards for what constitutes a dream, most of it does come from REM sleep. But if you ask about conscious mental experiences during sleep, we see it in all stages of sleep.
When we don’t get reports of mentation, it’s not even clear that it wasn’t there, as opposed to it didn’t carry over effectively into the waking state. So probably at least half of non-REM sleep, if you wake someone up, you get a report of some kind of mental activity, thoughts, images, hallucinations, emotions. It’s possible that’s going on all night long, we really can’t rule that out. But it is true that REM dreams and especially those later in the night are the most visual, the most complex narratives, the most emotional, the most bizarre. REM dreaming sort of gives you dreaming par excellence.
You posit that the function of dreams is to allow the brain to try out loose associations between thoughts. How do different dream stages affect this process?
There’s a cognitive task known as semantic priming. It’s a way of measuring the strength of associative connections in the brain. If I say fat, your brain says thin. And if I say short, your brain says tall. These are associations that come to mind very quickly. When you wake someone up from REM sleep and run them through 60 of these word pairs, you suddenly discover that they’re faster on hot–chocolate than they are on hot–cold. They’re faster on thief–wrong than they are on right–wrong. The brain seems to be selectively, preferentially, and certainly more rapidly accessing weak associations than strong ones.
If we wake them up from non-REM sleep or in waking, you get what you would expect, which is fastest for the strong associations. So in REM sleep, the brain circuitry is biased toward finding these weak associations. It might be that non-REM sleep is doing another part of the work, looking for medium level associations that might be useful.
Let’s say you wake people up from REM and non-REM and you collect the dream reports. If someone is dreaming about flying saucers in REM sleep, and you ask them why, they answer, “Oh, it’s because I love pizza.” But if you wake someone up from non-REM sleep, they say, “Oh, I was playing frisbee with my friends yesterday.” It will be a recent episodic memory for a non-REM source as opposed to a more semantic or distant episodic memory if it’s from REM sleep, The brain is basically using different algorithms to search through our memories to find associative memory that could possibly be of relevance to some apparently important event or unfinished business from the day.
What about lucid dreaming—when people know that they are dreaming? That feels like a very specific type of dream. Does it serve the same function as other dreams?
I don’t think anybody argues that we evolved to have lucid dreaming. It feels more like one of those things that just came about. Lucid dreaming might be a state where parts of your frontal cortex have come back online. That gives you some ability to discern the fact that you’re not in a real situation and also to gain some control over that situation. Certainly, I don’t think there is a particular function for lucid dreaming. I think of lucid dreaming as a tool.
Labs from around the world have done these wonderful experiments on lucid dreaming. They take lucid dreamers and they say, When you’re asleep, if you’re going to lucid dream, signal out with your eyes. You have control of the movement of your eyes when you’re in REM sleep, despite the rest of your body being pretty much paralyzed. People when they’re lucid can give these extreme left-right eye movements which show up in the electrooculogram that’s being recorded to signal “I’m lucid now.”
When you wake someone up from REM sleep and run them through 60 of these word pairs, you suddenly discover that they’re faster on hot–chocolate than they are on hot–cold.
In one study, researchers then ask sleepers questions. They will say to the person, in physiologically confirmed REM sleep, How much is eight minus four? and the person [moves their eyes] back and forth four times. In some cases, these people say, It sounded like the question came from somewhere else. Other people will say, I had the radio on, and it came out of the radio. So there’s various degrees to which the sensory input is put into the dream.
Most people have had a lucid dream or two in their lives. Very few people do it once a week, many more people do it once a month. Some people do it almost every night, but they’re rarities. I want to make clear that lucid means you’re aware of the fact that you’re dreaming. It does not mean you can take the dream and change it into anything you want it to be.
What about “dream hacking”? Is there any way to hack our dreams to improve our lives somehow?
Dream hacking is more interesting. Here’s an example: for the Superbowl, Coors is going to give you a 50 percent off on a 12 pack if you let them hack your dreams. In fact, if you pass the link on to a friend and they let Coors hack their dreams too, you could get that 12 pack for free.
It’s based on the work of a friend and colleague of mine, Adam Horowitz, and his Dormio device. It’s a fingerless glove you wear on your hand that measures the force of your muscles. The glove’s monitoring your hand as you’re trying to keep it more or less clenched. As you go to sleep, you think about the French Revolution. The glove monitors your hand and, of course, as you fall asleep, the tension in your hand relaxes. After you sleep for a minute or two, an app [linked to the gloves] wakes you up and says, “What was going through your mind just before you woke up?” and records it. Now you can go back to sleep and think about the French Revolution again. You’ll do this a half dozen times as you’re going in and out of sleep for the first half hour or so.
What Adam has shown is fascinating. Say he tells you to think about a tree as you go to sleep. Your dream reports move from the tree in my backyard to a tree with roses on it to a bunch of trees with giraffes flying above them to a flagpole on the moon. You can just feel the brain moving through these associative networks. Adam’s real desire is about creativity. He wants people to use this to access creative thinking powers, and he’s got some good examples.
Salvador Dalí had his key-over-plate technique. He sat in an armchair with his hand on the arm of the chair. He’d hold a key right over the end of the chair and think about a painting he wanted to make. As he fell asleep, the key dropped and woke him up, and he got an image in his mind from that brief period of break. He got these images that he then painted. Adam wants to ask the question, can everybody harness it? And the answer is they probably can.
Salvador Dalí had his key-over-plate technique. He’d hold a key right over the end of the chair and think about a painting he wanted to make. As he fell asleep, the key dropped and woke him up, and he got an image in his mind.
That was the original dream hacking, the original targeted memory incubation. Now Coors has you watch a 30 second animated film of mountain streams and glaciers and butterflies and Coors beer cans floating around with some music in the background. After watching this 30 second clip, you go to sleep and it replays tunes from inside the 30 second clip to reactivate those memories with the goal of producing alcoholics. We know that when you dream, your brain is finding and strengthening new associations. It’s doing them so that they will come to mind without effort when you’re awake, and without any knowledge of where they come from.
So if you see a stream, do you suddenly now feel an overwhelming need to get a Coors beer? This is evil shit. This is like the last bastion of our free mind, and we don’t want them to become littered like our highways are with billboards.