Why Do We Have Nightmares?

It’s evening, and my wife and I are tucking my son into bed. As he snuggles down into his pile of stuffed animals – he has a bunch, and all of them share his bed with him – he looks up at us. “why do we have nightmares?”

“Because your brain’s active,” my wife tells him, kissing him goodnight.

“Well, they shouldn’t give us nightmares!” he declares.

Can’t argue with that.

Nope, not really. I mean, I don’t remember my dreams with any frequency. Heck, I’m not positive I do dream most nights, although I have a vague recollection of learning that people go crazy if they don’t. But the nightmares stay with me. Even the ridiculous one where zombies flooded my condo, but they couldn’t find me because I’d climbed up on the back of my couch. Which, now that I think about it, wasn’t a nightmare precisely. I woke up more bemused than anything.

Why do we dream?

I’ve always thought that, if you described it to an alien, “sleeping” and “dreaming” would be two of the most ridiculous things you could possibly imagine. I mean, we spend about a third of our lives immobile and paralyzed, unaware of our surroundings, and hallucinating. It sounds like utter madness. And yet, we do it. Why?

Back in February 2015, Psychology Today said that “dreaming is:

  • A component and form of memory processing, aiding in the consolidation of learning and short-term memory to long-term memory storage.
  • An extension of waking consciousness, reflecting the experiences of waking life.
  • A means by which the mind works through difficult, complicated, unsettling thoughts, emotions, and experiences, to achieve psychological and emotional balance.
  • The brain responding to biochemical changes and electrical impulses that occur during sleep.
  • A form of consciousness that unites past, present and future in processing information from the first two, and preparing for the third.
  • A protective act by the brain to prepare itself to face threats, dangers and challenges.

Which of these theories is correct? Well, the answer right now seems to be “most, if not all, of them”. Our brains are complicated things, after all, and we don’t understand how and why they work anywhere as well as we’d like. As the article says, “There is not likely ever to be a simple answer, or a single theory that explains the full role of dreaming to human life. Biological, cognitive, psychological—it’s very likely that dreaming may serve important functions in each of these realms.”

So, why do we have nightmares?

It’s complicated.

All right, all right, I’ll see what I can find.

To start with, there’s The threat simulation theory of the evolutionary function of dreaming: Evidence from dreams of traumatized children, a sadly paywalled article that looks like it might give one possible explanation. Here’s what the abstract says:

The threat simulation theory of dreaming (TST) () states that dream consciousness is essentially an ancient biological defence mechanism, evolutionarily selected for its capacity to repeatedly simulate threatening events. Threat simulation during dreaming rehearses the cognitive mechanisms required for efficient threat perception and threat avoidance, leading to increased probability of reproductive success during human evolution. One hypothesis drawn from TST is that real threatening events encountered by the individual during wakefulness should lead to an increased activation of the system, a threat simulation response, and therefore, to an increased frequency and severity of threatening events in dreams. Consequently, children who live in an environment in which their physical and psychological well-being is constantly threatened should have a highly activated dream production and threat simulation system, whereas children living in a safe environment that is relatively free of such threat cues should have a weakly activated system. We tested this hypothesis by analysing the content of dream reports from severely traumatized and less traumatized Kurdish children and ordinary, non-traumatized Finnish children. Our results give support for most of the predictions drawn from TST. The severely traumatized children reported a significantly greater number of dreams and their dreams included a higher number of threatening dream events. The dream threats of traumatized children were also more severe in nature than the threats of less traumatized or non-traumatized children.

Now, I’m not a psychologist or a neuroscientist, but “threatening dream event” sounds like a technical term for “nightmare”. So, speculating entirely from the abstract and wishing I could read (and try to make sense of) the article, it seems entirely reasonable that nightmares are – among other things – a threat response rehearsal. And I’d be curious to know if the “threatening dream events” of the traumatized children strongly related to the events that caused the trauma.

Both Psychology Today and LiveScience seem to agree, at least in broad strokes. “Most nightmares are a normal reaction to stress, and some clinicians believe they help people work through traumatic events,” reports Psychology Today, while LiveScience quotes Doctor Deirdre Barrett as saying that “Nightmares probably evolved to help make us anxious about potential dangers. Even post-traumatic nightmares, which just re-traumatize us, may have been useful in ancestral times when a wild animal that had attacked you, or a rival tribe that had invaded might well be likely to come back.”

So why am I dreaming about zombies?

Clearly, zombies aren’t a genuine potential danger, no matter how scary George Romero made them seem. Doctor Barrett, however, gave us some more information to consider: “However, some nightmares may be calling to your attention something you might do well to worry about or something that, once you are more conscious of the concern, you can convince your unconscious to stop wasting time on.”

So, I’m going to speculate here. Clearly, zombies aren’t real. Heck, for most of us, being eaten by a lion isn’t a real threat either. But your brain isn’t going to to generate a block of text in your dreams, telling you to be concerned about your spending habits and the amount of debt you’re carrying. No, it’s going to respond to your current stress in the office by trying to stage a dry run threat response drill. By making you practice running from popsicle-men wielding pinking shears for three virtual days. Because, your brain assumes, you’re obviously needing to run from something.

Do we go crazy if we don’t dream?

Well, the (fictional) Russian Sleep Experiment notwithstanding, the answer is pretty much “no”. At least, according to Harvard University. Mostly, when you don’t sleep, you get tired. Obvious, right? Well, that lack of sleep causes you to make poor decisions. Increased accidents are common, as are lack of focus and higher-level cognitive functioning – that’s concentration, memory, and the ability to do math and even reason logically.

But that’s sleeping. What about dreaming? Well, according to the Encyclopedia Britannica online, animal experimentation has revealed heightened levels of sexuality and aggressiveness after REM-sleep deprivation. Beyond that, there isn’t a whole lot of impact. In fact, there appears to be some value to REM sleep deprivation as a treatment for depression. So, no. You won’t go crazy. Just horny and aggressive and too tired to act on it.

Why Does Size Matter Not?

I’ve been home sick for a couple of days, and I’m feeding my son breakfast before getting him off to kindergarten and then collapsing on the couch. He loves it. He’s taking the opportunity to ask me questions (“how would you blow up a planet?”), and talk to me, and show off his progress reading.

“Dad,” he asks, “what did Yoda mean when he told Luke that size matters not when your ally is the Force?”

“Well, son,” I say, trying to use this as a teaching moment, “it’s all about how he lifted the X-wing. Did he use his muscles, and drag it out of the swamp?”

“No,” my son said.

“You’re right. He used the Force.” I leaned forward, just a little. “And he meant that, if you believe in yourself and believe you can succeed, you can do anything you want.”

He considered that, then last ones at me. “Dad?”

“Yes, son?”

“Would you rather fly an X-wing, or the Death Star?”

This is going to be a little different, isn’t it?

Yep. Believe it or not, this isn’t a science blog. It’s a blog dedicated to trying to answer my son’s questions. It’s just that, most of the time, he asks questions that I can answer with science.

Size matters not

This really isn’t one of those questions. I mean, sure. There are probably studies on confidence and how it generates success. But that’s not the point, not really.

My son is six. To him, the world is a huge, exciting place filled with wonder and possibility and excitement. And, thanks to him, I’m being reminded that the world is filled with wonder and possibility and excitement. So, as I see it, it’s my job to encourage him and teach him and help him take advantage of everything the world offers.

That starts with confidence.

See, I’m well aware that there are things that are by definition impossible. But I’m also aware that, all too often, we look at things that are merely difficult and declare them “impossible”. “I can’t get out of debt.” “My family can’t make it on one income.” “I’ll never get in shape.” “I’ll never be able to retire.” A million fears become a million reasons to never try.

I don’t want my son to learn that. Not from me, anyway. “Dad,” he’ll say, “I’m going to build a robot!” Or he’ll declare to me that he’s going to build a speeder bike, or a lightsaber, or buy a house next to us so we won’t get lonely, or that he’s going to fly. And it would be easy to accidentally crush his dreams, in the name of “teaching” him.  Instead, I try to respond with this: “Cool! That might be hard, though. How should we start?”

“So certain are you. Always with you it cannot be done. Hear you nothing that I say?”

For the record, we have never built a robot, or a speeder bike, or a lightsaber that works outside our imaginations. That’s mostly due to the fact that sticks and rocks and Legos and paper aren’t the optimal components for such things. But we’ve spent hours working on them, and chasing each other with them, and playing and learning.

My son’s got plenty of time to learn that some things may very well be actually impossible. Right now, though, he’s learning a more important lesson: if you fail, and you still want to do it, try doing it a different way.

“Size matters not, when your ally is the Force.” Sure, I can’t teach my son to move an X-wing with his mind. But I can teach him that it can be moved, and that he can use his mind to figure out the way. And I can teach him to try again, and try something different, if he doesn’t succeed. And to remember that you don’t fail unless you give up.

In the process, maybe I’ll learn it again for myself.

What is “the Unknown”?

Every once in a while, these questions get abstract.

I stayed home from work yesterday, because my son had an ear infection and the doctor told us to keep him home from daycare for the first day. (That, by the way, is always a fun dilemma for two working parents.) He wasn’t feeling bad, so keeping him corralled was an interesting exercise. So we watched The Year Without A Santa Claus and Nestor the Long-Eared Donkey. And by then, much as I love the holidays, I was ready for a change. So I talked him into watching Sinbad and the Eye of the Tiger. Chunks of it went right over his head, but he loved it.

There’s one sequence, though, that inspired some lovely discussion. Melanthius, a Greek mystic (played by Patrick Troughton, who’s about as Greek as I am) is discussing the reaction of the “troglodyte” to a sketch of the gate they’re looking for. He says “Like all primitives, he’s afraid of the unknown”. Unlike us modern, civilized people, who are utterly comfortable with the unknown…


“What’s the unknown?” my son asks. And it’s a good question, because I don’t think that’s a word he’s heard before. The problem I run into, as I try to explain it to him, is that he’s convinced that “the unknown” is a thing in the movie. I tell him “it’s something you don’t know”, and he says “is the door the Unknown?”

“No, son. The unknown is something you don’t know.”

“Maybe the unknown is a ghost!” he says.

“Well,” I guardedly allow, “it could be…”

“Or a dragon!” he continues. “Or a dragon that shoots ghosts!”

After a while, I think I got him to understand that “the unknown” isn’t a thing. But five-year-olds don’t do so well with abstract concepts. So, let’s go ahead and talk about it here.

What is the unknown? And why do we fear it?

To start with, Merriam-Webster defines the word as follows:

adjective un·known \-ˈnōn\

1: one that is not known or not well-known; especially : a person who is little known (as to the public)
2: something that requires discovery, identification, or clarification: as
a : a symbol (as x, y, or z) in a mathematical equation representing an unknown quantity
b : a specimen (as of bacteria or mixed chemicals) required to be identified as an exercise in appropriate laboratory techniques

The etymology of the word comes from the prefix un- and the word known. Un- is either a prefix of negation, deriving from the coming to us from the Proto-Germanic *un-, or a prefix of reversal, deprivation, or removal coming from the Proto-Germanic *andi-. Know derives from the Old English cnawan “to know, perceive, acknowledge, declare”, which derives from the Proto-Germanic *knew-.

(“Unknown” clearly uses the “prefix of negation” form of un-. But it’s an interesting mental exercise to think of what it would mean if you interpreted un- as the “prefix of reversal, deprivation, or removal” instead. “Unknown” would then mean something that was forgotten, possibly deliberately.)

So the unknown is simply something representing an unknown quantity, or something that requires discovery and/or identification. That doesn’t seem like something frightening, put like that. But… we do fear the unknown. Why?

The National Institute of Mental Health defines fear as “a feeling of disquiet that begins rapidly in the presence of danger and dissipates quickly once the threat is removed. It is generally adaptive.” Adaptive, of course, is referring to an “adaptive trait”, which is something that is evolved and maintained by natural selection. So fear is an evolved response, triggered by the “fight or flight response” (properly known as General Adaptation Syndrome).

From here on out, you’ll be reading my opinion.

Fear is an adaptive survival response – we’ve evolved from a long line of critters that had a healthy fear reaction. After all, the Juramaia sinensis() that didn’t have enough sense to be afraid of predators didn’t breed. And, from a “I don’t want to get eaten” perspective, being afraid of something you can’t see and/or don’t understand makes sense. That new animal might be a predator. That dark hole might be really deep. That strange, moving thing might try to kill you.

Humans have imaginations. We can visualize things that aren’t there. (Interestingly, though, it turns out that other animals – our close cousins the Chimpanzees and the Great Apes, but apparently also rats – can as well, based on observational and brain activity studies. So imagination isn’t a uniquely human trait.) Combine that ability with an instinctive fear reaction, and you get the ability to be afraid of things that are unknown. So while we should respect and listen to that fear as a way of staying alive, we shouldn’t let ourselves be ruled by that fear. After all, once we quantify and understand that unknown, it may very well not be dangerous.

Unless it turns out to be a dragon that fires ghosts. I’m all in on fearing that.

Can we read Star Wars again tonight?

I’m getting my son ready for bed when this particular question gets asked.  It’s not a surprising question, really. He’s 5, and he’s fallen in love with the series just as hard as he did with Thomas the Tank Engine when he was two.  I can’t even blame him – I was six  when the original movie came out, and I did the same thing.

“No,” I answer.

“Why not?” he asks, picking up his Little Golden Book edition of Rerurn of the Jedi.

“Because daddy’s tired of reading Star Wars,” I answer, because I’ve read – or listened to my wife read – that same exact story for most of October.  And then I wait, pretty sure I’ll cave in if he asks. Fortunately for my sanity, he picks another book and we read about trains instead.

All of which got me wondering:  why do we get bored?  I mean, I love Star Wars. Why do I get tired of reading it, or watching it?  Wouldn’t it make more sensed I wanted to keep doing something I enjoyed?

It turns out that there’s a number of theories about boredom. Psychology Today published an article suggesting that it was a way to make the brain more efficient with drugs.

Here’s the idea. Your brain works a lot. For example, you focus on something new twice a second. If you spot something interesting, your brain dumps a hit of opioid chemicals, which encourages you to focus on that thing – freeing up resources for other tasks. But the opioid fix wears off, and so you go looking for something new to get a new fix.  (This may also explain why the first bite of ice cream is the best…)

So, if this theory is true, the more accurate answer to “why not” would have been “because daddy is jonesing for some of that sweet brain heroin”.