The study of dreaming is called oneirology, and it's a field of inquiry that spans neuroscience, psychology, and even literature. Still, the plain fact is that the reasons why we dream are still mysterious. But that hasn't stopped scientists from coming up with some pretty fascinating hypotheses. Here are ten of them.
1. Wish fulfillment
One of the first sustained efforts to study dreams scientifically was spearheaded by the psychoanalyst Sigmund Freud, in the early twentieth century. After analyzing the dreams of hundreds of his patients, he came up with a theory that still resonates with a lot of researchers today: dreams are wish-fulfillments. Any dream, no matter how terrifying, can be looked at as a way of getting something that you want, either literally or symbolically. For example, say you have a terrifying and sad dream about your mother dying. Why would that be a wish-fulfillment? Maybe, Freud would say, you are having a conflict with your mother that would be easily resolved if she were out of the picture. So you don't want your mother to die, but you do want to deal with that conflict. By thinking of dreams in this light, Freud was able to help many of his patients unbury hidden emotions that they hadn't dealt with.
2. An accidental side-effect of random neural impulses
If you buy into Freud's idea about dreams, their subject matter is deeply meaningful. They can reveal wishes or emotions you didn't realize you had. But another popular school of thought holds that dreams are actually just a kind of brain fart, an accidental side-effect of activated circuits in the brain stem and stimulation of the limbic system that's involved with emotions, sensations and memories. J. Allan Hobson, the psychiatrist who popularized this idea, calls it the "activation-synthesis theory." In a nutshell, the brain tries to interpret these random signals, resulting in dreams.
What's particularly interesting about this theory is that it could also help to explain why humans use storytelling as a way to make sense of an often random, chaotic universe. If dreams are the meanings our brains supply to random neural firing in our limbic system, then stories are like waking dreams, meanings we use to paper over the fundamentally disorganized signals we receive from the world around us.
3. Encoding short-term memories into long-term storage
Maybe dreams are just randomly-generated stories caused by neural impulses, but perhaps there's also a reason for them, too. To explore this idea, psychiatrist Jie Zhang, proposed the continual-activation theory of dreaming, which refers to the idea that our brains are always storing memories regardless of whether we're awake or asleep. But dreams are a kind of "temporary storage" area of consciousness, a spot where we hold memories before we move them from short-term to long-term storage. They flash through our minds as dreams before we secret them away in the files of our memory.
4. Garbage collection
Dubbed the "reverse learning" theory, this idea suggests that we dream to get rid of undesirable connections and associations that build up in our brains throughout the day. Basically, dreams are garbage collection mechanisms, clearing our minds of useless thoughts and making way for better ones. Essentially, we dream in order to forget. Dreams help us eliminate the information overload of daily life and retain only the most important data.
5. Consolidating what we've learned
This theory flies in the face of the reverse learning theory, by suggesting that we actually dream to remember rather than forget. It's based on a number of studies that show people remember what they've learned better if they dream after learning it. Like Zhang's theory about long-term memory storage, this theory suggests that dreams help us retain what we've learned.
The theory is bolstered by recent studies on trauma, which suggest that when people go to sleep right after a traumatic experience that they are more likely to remember and be haunted by the trauma. So one form of triage for traumatized people is to keep them awake and talking for several hours, even if they are exhausted, to prevent this traumatic memory consolidation from happening.
6. An evolutionary outgrowth of the "playing dead" defense mechanism
Based on studies that revealed strong similarities between animals who are playing dead and people who are dreaming, this theory suggests that dreaming could be related to an ancient defense mechanism: tonic immobility, or playing dead. When you dream, your brain behaves much the way it does when you're awake, with a crucial difference: chemicals like dopamine associated with movement and body activation are completely shut down. This is similar to what happens to animals who undergo temporary paralysis to fool their enemies into thinking they've died. So it's possible that dreams began as a defense mechanism which our bodies retained — in a different form — as we evolved into creatures who no longer experienced tonic immobility.
7. Threat simulation
The "playing dead" theory of dreams actually fits in nicely with another evolutionary theory of dreams, developed by philosopher-neuroscientist Antti Revonusuo in Finland. He suggests that "the biological function of dreaming is to simulate threatening events, and to rehearse threat perception and threat avoidance." People who have these kinds of dreams will be better able to face threats in their waking hours, because they've already run through these nighttime simulations. As a result, people who dream in this way will survive more often, to pass on their genes. Unfortunately, this theory doesn't explain my recurring dream of eating brownie sundaes.
8. Problem solving
Building on ideas like Revonusuo, Harvard medical researcher Deirdre Barrett suggests dreams are a kind of theater in which we're able to solve problems more effectively than when we are awake — partly because the dreaming mind makes connections more quickly than the waking mind does. This idea is based in part on experiments she did where people were asked to solve problems while "sleeping on them." The problem-solving outcomes were better for the subjects who dreamed.
9. Oneiric Darwinism
Maybe the idea of solving problems in our sleep is itself a kind of Darwinian process. Psychologist Mark Blechner says the reason we dream is:
[To] create new ideas, through partial random generation, which can then be retained if judged useful… Dreams introduce random variations into psychic life and internal narratives. They produce ‘thought mutations.’ Our minds can then select among these mutations and variations to produce new kinds of thought, imagination, self-awareness, and other psychic functions.
Basically, dreams are natural selection for ideas. This can extend to the level of emotions, too. One group of researchers suggest that dreams are places where we run through situations and try to select the most useful emotional reactions to them. Psychologist Richart Coutts suggests that this is one way we figure out the best way to react to situations emotionally, and why we often feel better about painful issues the morning after a night of dreams.
10. Processing painful emotions with symbolic associations
While a Darwinian model of dreaming suggests we are aggressively mutating our ideas, or weeding out maladaptive emotions, a new model of dreaming suggests that the process is more like therapy than evolution. We aren't aggressively selecting for the most adaptive idea or emotion — we are just running through those ideas and emotions and placing them in a broader psychological context. Often, the brain does this by associating an emotion with a symbol.
Psychiatrist and sleep disorder expert Ernest Hartmann calls this simply the Contemporary Theory of Dreaming. He writes:
When one clear-cut emotion is present, dreams are often very simple. Thus people who experience trauma—such as an escape from a burning building, an attack or a rape—often have a dream something like, "I was on the beach and was swept away by a tidal wave." This case is paradigmatic. It is obvious that the dreamer is not dreaming about the actual traumatic event, but is instead picturing the emotion, "I am terrified. I am overwhelmed." When the emotional state is less clear, or when there are several emotions or concerns at once, the dream becomes more complicated. We have statistics showing that such intense dreams are indeed more frequent and more intense after trauma. In fact, the intensity of the central dream imagery, which can be rated reliably, appears to be a measure of the emotional arousal of the dreamer. Therefore, overall the contemporary theory considers dreaming to be a broad making of connections guided by emotion.
He speculates that this kind of association between emotion and symbol helps to "tie down" the emotions and weave them into our personal history. Possibly, this kind of symbolic association was an evolutionary adaptation that helped our ancestors cope with trauma in a world where they would have dealt with far more life-threatening events on a daily basis than most of us do today.
Ultimately, this hypothesis brings us back to the storytelling component of dreams. We seem to use these bizarre images and ideas to make sense of the day's events, to turn random neural firing into something coherent, and even to figure out how we should feel about what's happened to us. There is no doubt that dreams play a major role in our thought processes. The question remains, however: Are they an evolutionary adaptation, or just an uncanny accident?
All images taken from The Fountain. Sources linked in the text.