Why we dream: an open question
People have asked why we dream for as long as we've been dreaming, and science still has no single answer. We know a fair amount about when we dream and what the brain is doing at the time, but much less about what dreaming is for, if it's for anything in particular.
The theories below aren't teams where only one can win. Some are about cause, what produces dreams in the brain, and others are about function, what dreams might be good for. Several fit together. Read them as hypotheses still under debate, not closed cases.
That also changes how you read your own dreams. If no theory has the last word, what a dream means for you depends mostly on your life, your feelings, and what it stirs up when you remember it.
Freud: dreams as disguised wishes
Sigmund Freud's theory was the first great modern account of dreams. In The Interpretation of Dreams, published in late 1899 with a date of 1900 on the title page, he argued that dreams fulfill wishes, often wishes we won't admit to while awake.
For Freud, every dream has two layers: the manifest content, the story you remember, and the latent content, the hidden wish behind it. Between the two sits a kind of censor that disguises the wish with symbols, displacements and blends so that it doesn't wake you. Interpreting a dream meant undoing the disguise through the dreamer's own associations.
His influence was huge, in psychology and far beyond. Carl Jung, who worked with Freud before breaking away, saw dreams less as disguised wishes and more as a way of balancing what the conscious mind neglects. The main criticism of Freud is that his ideas are hard to test: almost any dream can be read as a wish if you look hard enough. Still, his habit of paying attention to your own associations lives on in many kinds of therapy.
Activation-synthesis: the brain making sense of noise
The activation-synthesis hypothesis was put forward in 1977 by Harvard psychiatrists J. Allan Hobson and Robert McCarley. They started from the biology of REM sleep: during that stage, the brainstem sends strong and largely random signals up to the cortex.
In this view, the cortex does what it always does with incoming signals. It tries to make sense of them, weaving them together with stored memories and emotions. The dream is that synthesis, a story improvised from activity that carried no message to begin with. That would explain why dreams are so strange, with no need for a censor.
The theory was hugely influential and hotly debated. One problem is that people also dream outside REM. The neuropsychologist Mark Solms, drawing on patients with brain injuries, argued that dreaming depends on forebrain circuits tied to motivation, not just on the brainstem. Over the years Hobson revised and expanded his own model.
Threat simulation: rehearsing danger
The threat simulation theory, from Finnish psychologist Antti Revonsuo, proposes an evolutionary purpose: dreaming is a simulator where the brain rehearses spotting and escaping danger. Far back in our species' history, practicing escape or defense during sleep would have given people an edge against real threats.
The theory fits something many people notice: dreams of being chased, falling, running late or facing an exam are extremely common around the world. A study by Revonsuo's group also found that severely traumatized Kurdish children recalled more dreams, with more threats in them, than Finnish children without that experience.
The main criticism is that plenty of dreams contain nothing threatening at all, and that dream rehearsals rarely end with a good solution. So some researchers see it as an explanation for certain kinds of dreams, not all of them.
Memory consolidation: replaying what we learn
The memory consolidation theory builds on something well established: sleep helps us lock in and reorganize what we learn. The open question is whether dreams are part of that work or just come along for the ride.
In a 2010 study in Current Biology, Erin Wamsley, Robert Stickgold and colleagues taught volunteers to find their way through a virtual maze. People who napped and dreamed about something related to the task improved much more when they tried it again than those who didn't. The dreams almost never replayed the maze itself; they mixed bits of the task with older memories.
The authors were careful: the study doesn't show that dreaming causes learning, only that dreams may be a sign the brain is processing that memory. That blend of the recent and the long ago looks a lot like what anyone finds when rereading a dream journal.
Emotional regulation: overnight therapy
The emotional regulation theory holds that dreaming, especially during REM sleep, helps us process the day's feelings and take some of the sting out of them. Psychologist Rosalind Cartwright, who spent years studying the dreams of people going through divorce, found that those whose dreams about their ex were more emotional, and who played a more active part in them, tended to come out of depression better than those whose dreams were flat and thin.
In 2009, Els van der Helm and Matthew Walker pulled together evidence from many studies in a review titled, question mark included, Overnight therapy? They proposed that REM sleep lets the brain reprocess emotional memories in a calmer chemical state, keeping the lesson while softening the pain.
This idea has a clear limit. After trauma, nightmares can repeat night after night without bringing any relief. If that's happening to you, it isn't something you have to solve through your dreams: a mental health professional can help, and there are treatments designed specifically for nightmares.
The continuity hypothesis: we dream about what matters to us
The continuity hypothesis holds that dreams largely reflect the concerns, relationships and interests of waking life. It grew out of the work of psychologist Calvin Hall, who gathered thousands of dream reports, and the content analysis system he published in 1966 with Robert Van de Castle.
Sociologist and psychologist G. William Domhoff carried that work forward with long dream series from single dreamers. He found that the people who show up most in someone's dreams tend to be the ones who matter most to them, and that the way the dreamer relates to them in dreams echoes waking life.
Continuity doesn't mean we dream about yesterday exactly as it happened. It's more about themes and feelings than specific events, and researchers still argue over how to measure it. Even so, it's the idea closest to what a dream journal does: looking in your dreams for whatever occupies you by day.
What to do with these theories
None of these theories can tell you what last night's dream meant, but together they offer useful questions for thinking it through. Try them as different lenses when you reread what you wrote down:
- Continuity: what person, theme or worry from your life shows up here?
- Emotion: what did you feel in the dream, and where do you feel something similar by day?
- Threat: if there was danger, what was the dream rehearsing: running, facing it, asking for help?
- Memory: what mix of recent and old do you recognize?
- Associations: what comes to mind with each image, without judging it?
Frequently asked questions
Which theory of why we dream is correct?
There's no theory that everyone accepts yet. Many researchers think dreams may have several causes and functions at once, and that each theory explains some kinds of dreams better than others.
Can dreams predict the future?
There's no scientific evidence that dreams foretell events. Sometimes a dream reflects something you already sensed or feared, which is why it can feel like a premonition. Reading dreams as a reflection of your present tends to be more useful.
If I dream about something, does it mean I want it?
Not necessarily. That was Freud's idea, but other theories see dreams as worries, fears, memories or feelings still being processed. A violent or uncomfortable dream doesn't reveal a hidden wish or say who you really are.
Why do some people say they never dream?
Almost everyone dreams every night, but how much people remember varies a lot. If you tend to wake from dreamless stages or jump straight out of bed, dreams slip away easily. Jotting down whatever you recall each morning usually helps.
Further reading
- Sigmund Freud, The Interpretation of Dreams (1899, dated 1900)
- J. Allan Hobson and Robert W. McCarley, The brain as a dream state generator: an activation-synthesis hypothesis of the dream process, American Journal of Psychiatry 134(12), 1335–1348 (1977)
- Mark Solms, Dreaming and REM sleep are controlled by different brain mechanisms, Behavioral and Brain Sciences 23(6), 843–850 (2000)
- Antti Revonsuo, The reinterpretation of dreams: an evolutionary hypothesis of the function of dreaming, Behavioral and Brain Sciences 23(6), 877–901 (2000)
- Katja Valli et al., The threat simulation theory of the evolutionary function of dreaming: evidence from dreams of traumatized children, Consciousness and Cognition 14(1), 188–218 (2005)
- Erin J. Wamsley, Matthew Tucker, Jessica D. Payne, Joseph A. Benavides and Robert Stickgold, Dreaming of a learning task is associated with enhanced sleep-dependent memory consolidation, Current Biology 20(9), 850–855 (2010)
- Els van der Helm and Matthew P. Walker, Overnight therapy? The role of sleep in emotional brain processing, Psychological Bulletin 135(5), 731–748 (2009)
- Rosalind D. Cartwright, The Twenty-four Hour Mind: The Role of Sleep and Dreaming in Our Emotional Lives (2010)
- Calvin S. Hall and Robert L. Van de Castle, The Content Analysis of Dreams (1966)
- G. William Domhoff, The Scientific Study of Dreams: Neural Networks, Cognitive Development, and Content Analysis (2003)
Dreams are personal: these readings invite you to reflect, they don't decide for you. They are not medical or psychological advice. If you have frequent nightmares or sleep badly, see a professional.