The Science of Dreams & Nightmares

Before the enlightenment, it was long believed that dreams were either prophecies, omens or even communication from gods, angels and devils. But, as time has gone by, we've slowly but surely been demoting dreams from this holy pedestal down to a much more humble, secular stool.
In the late 1800s, rather than messages from a god, early psychology researchers like Jung and Freud thought these were messages from... ourselves - that our dreams represented thoughts and feelings that our subconscious minds wished to express, of which our conscious minds were unaware.
And in the late 1900s, we reduced this further from genuine messages, down to random firings of the brain - akin almost to a myoclonic jerk, a jolt of energy down the line to make sure all of the wiring remains active whilst your brain was in "standby" mode.
But now, we've entered the 2000s, and this steady demotion has come to a halt. Researchers are starting to re-examine if dreams may be more than random brain misfirings.

For instance, we've come to learn that humans are not alone when it comes to dreaming. All mammals, most birds and even some reptiles which have been studied by dream researchers have been found to dream, based on studying their brain activity during sleep. This isn't true of all animals - what research has been done on fish implies that they don't dream, and insects also don't appear to (although, I didn't find much research on insect dreams, so this might be a pragmatic assertion rather than empirically proven).

Since the main difference between fish brains and mammal brains is their small size and underdeveloped forebrain, it appears that dreams aren't some dysfunction caused by having evolved a human brain, but rather it seems to be an innate function of all brains with a developed cerebral cortex and/or the hippocampus.
Not to mention, it's not exactly a function of "sleep", since we can sleep without dreaming. According to neurologists and brain researchers, there are three states of wakefulness: awake (completely awake), REM Sleep (asleep, and dreaming) & NREM Sleep (asleep, and not dreaming). And whilst REM sleep is natural and has benefits, mentally... it's not always necessary. These are fringe cases, but if someone is chemically or medically prevented from having REM sleep, they can suffer little to no ill effects, which means REM sleep isn't necessary for functioning...

So, it's left researchers asking why? After all, every function of the body seems to have a use or a reason. Yes, even the dumb ones. Ever had a brain-freeze? It's actually a dysfunction of your body attempting to keep your face warm. Because the pain receptors at the back of your palate follow the trigeminal nerve - the same nerve the connects to pain receptors in the face - when you feel cold at the top and back of your throat, it causes those same pain receptors in your palate to fire, and misconstrues the cold as coming from your face, causing your veins to vasoconstrict and -dilate, quickly, in an attempt to warm your face, which causes a brief headache. It's function is to re-warm your face.
And, ever hit your funny bone? It's actually due to the evolution of your arms. The ulnar nerve is a nerve that goes from your spine to your little finger and ring finger, and so from the spine to your pinkie, heading around your elbow is the most direct route. (Note: Keep in mind also that arms and nerves - and the rest of your body - would have evolved and developed simultaneously). And as we required more muscle for stronger arms, the hinge of the elbow joint would have exposed the ulnar nerve, so now when your bent elbow is hit, your body sends that stinging jolt of pain, warning you that it's a vulnerable spot. It hurts, and it's imperfect, but it has a distinct purpose.

So... what function or design purpose does a "dream" serve? Or, even, what dysfunction or malfunction caused it? Well, there are a few theories.

One is the Activation-Synthesis Hypothesis. It was proposed in Hobson, J. and McCarley R.'s 1977 paper "The Brain as A Dream State Generator: An Activation-Synthesis Hypothesis of the Dream Process", which was published in The American Journal of Psychiatry, that dreaming was caused by sporadic activation of the brain during sleep, which is later remembered upon waking and synthesized into something coherent. It's a fascinating little tidbit, but in a follow-up paper, the theory changed
In Hobson J.'s 2020 paper "REM sleep and dreaming: Towards a theory of protoconsciousness" from Nature Reviews Neuroscience, this hypothesis evolved into a new model of a vestigial mental proto-self that we're all born with. Basically, the theory is that consciousness is something that must grow and develop throughout our life, which is why memories of being a baby are so vague, we don't have a fully developed consciousness. However, Hobson proposes that our consciousnesses are developed because we are born with a protoconsciousness, a kind of "mental model of self" that's underdeveloped, but based on the idea that we can control our body, and move it. And the theory suggests that after we develop a mature, self-aware consciousness, we still retain this proto-consciousness, in the form of a "dream-self" that is aware and mindful in our dreams.

It's an interesting hypothesis, extrapolating from some fascinating experiments showing evidence of the various dream-states in humans. That being said, uh... proto-consciousness? Dream-self? Yeah, I don't believe they've substantiated these concepts and it's pretty out there, but it's a fascinating model nonetheless.
But, that's just dreams - what of nightmares, then?

The Threat Simulation Theory was first proposed by Revonsuo. A, in their 2000 paper "The reinterpretation of dreams: An evolutionary hypothesis of the function of dreaming" in Behavioral and Brain Sciences. In this paper, inspired by evolutionary psychology, it was proposed that the purpose of dreams was, essentially, a kind of low-fi virtual reality for mammals to "practice" being attacked and learning to survive without the threat of death. This would give dreaming a definite purpose - and the theory proposes the reason why we don't have nightmares as often now, is because threat simulation is a defense mechanism, activated by threatening stimuli.
In fact, in a later paper in 2005 by Valli K., Revonsuo. A, et al, called "The threat simulation theory of the evolutionary function of dreaming: Evidence from dreams of traumatized children", published in Consciousness and Cognition, it was shown, by studying the dreams of children suffering from PTSD, and comparing their dreams with those who did not, that there was a positive correlation between being traumaitized in real life, and simulating that threat in one's nightmares.

That's... creepy. Even if you set aside the thought of scientists studying traumatized children to quantify how many nightmares they have - according to this theory, when you think about it, what it effectively means is that dreams only exist so that we can have nightmares... okay, yeah, that's not terrifying at all.

There's also hypotheses like the Defensive Activation Theory. Proposed by Eagleman D. & Vaughn D in their 2021 paper "The Defensive Activation Theory: REM Sleep as a Mechanism to Prevent Takeover of the Visual Cortex", published with Frontiers in Neuroscience, which proposes that, because of neuroplasticity, our brains function on a "use it or lose it" system. Basically, neuroplasticity is the continuing growth and rewiring the the brain. You can see this in people who suffer from brain trauma, and lose brain function, who through rehabilitation can relearn to speak, walk or any number of other brain functions. Our brains are pattern-seeking machines, which means they are always trying to find connections, and the paper mentions how other researchers have provided evidence that this kind of rewiring can occur in a matter of hours.
Therefore, according to this paper's model, if portions of our brain - such as the visual cortex - were left idle for eight hours every day, then it would be vulnerable to this neuroplasticity, meaning we could gradually lose our ability to see as other regions of the brain try to rewire this "unused" brainspace. Basically, if we stop "looking" we'll lose the ability to see. So, dreams exist to create "false" visuals, to keep the visual cortex (and other associated brain regions) mildly active, to prevent other brain regions from taking over "unused" space.

So, uh... if you didn't dream, your brain will eat itself. Y'know, I didn't start doing this research to be horrified, but I'm kind of horrified right now.

But, on a much less disturbing note, another more recent and well-substantiated theory of dreaming is the Emotional Re-Processing Theory. As described in Scarpelli S., et al's paper "The Functional Role of Dreaming in Emotional Processes" published in Frontiers in Psychology in 2019, the scientists investigated the role that dreaming plays in memory - not only autobiographical memory, but also dream-experience memory - and because of this known link, the paper was exploring the effects of REM sleep on the consolidation of emotional memory.
See, it's already known that dreaming helps your memory - people remember better if they dream, there's research showing that. But, this paper was trying to explain that link, and they have a pretty fascinating theory. See, you have a lot of memories, and the best way to deal with them all is to sort them using a system. But your brain doesn't use chronological or alphabetical order, it actually works based on emotions. I think of it like twitter hashtags, just like on twitter people use hashtags to correlate similar tweets, or whatever you twits do on there... well, your brain basically uses emotions as hashtags: "the day my father died, #sad", "my first rollercoaster ride #happy #scary", "that time I puked on myself at graduation #disgust #shame" That's a simplification, but it's the basic idea. If you feel angry, you're more likely to remember angry things - you've clicked the "angry" hashtag in your memory.
Well, this study showed a correlation between dreaming and emotional memory, empathy and of course, memory. Because the areas of your brain that contribute to dreaming also contribute to emotion, and the theory is that because you are feeling emotions during your dreams, this is basically giving your brain twice the practice of feeling things as it would if you only felt emotions whilst awake, and it re-feels emotions that were poorly regulated or misunderstood, to give you more experience with them.

So, if you're a "dreamer", you're a more emotionally intelligent person, according to that theory. That makes poetic sense, but I guess now it makes scientific sense. I think of it like it's trying to get you to re-digest memories which gave you mental indigestion. This also explains why PTSD sufferers have trauma nightmares - it's trying (and failing) to get you to cope with emotions you struggled with, not realizing that you won't.

- - -

These are just a few theories, and the reality is that brains are complicated, and not all of these theories are mutually exclusive, and whilst I have my doubts about some, there is some truth in them all - they are all based on experimental, empirical data, after all. But my main take-away is that dreams are not just random misfirings of the brain. That's not to say that they are a coherent, purposeful messages, but those signals and the visions that they entail may well have a distinct purpose in our waking lives. What do you think?

Also, before I go, I want to take a moment to let you know - the reason I am writing this is because in an upcoming post, I plan on talking about dream interpretation and the mythology of dreams, so I wanted to first cleanse my palate by looking at the science, and feel better about sharing a whole lot of nonsense by first sharing something educational. But I had no idea that half of these theories would be brains eating themselves, and the implication that we evolved to have nightmares. It's apt for a Halloween Countdown, but I genuinely wasn't expecting it. Once again, science proves that truth can be stranger than fiction.
Until Next Time, I'm the Absurd Word Nerd, and good night.