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.