What are dreams? What the science actually says

Every night, you spend roughly two hours in a world only you have access to. You fly over landscapes, meet people you don’t know, or live through scenarios that feel real until you wake up. Dreams have fascinated people for thousands of years, from ancient oracles to modern sleep laboratories. But what actually are dreams? Why does the brain spend so much energy building these nightly stories? Even though research has come a long way, there’s still no single, simple explanation. Let’s look at what we actually know.

The stages of sleep — where dreams live

To understand dreams, we first need to understand sleep. Sleep isn’t just a passive state where the body switches off. It’s an active process with several distinct stages, and each stage has its own function.

A typical sleep cycle lasts around ninety minutes and repeats four to six times over the course of a night. The cycle consists of four stages. The first three are called NREM sleep (non-rapid eye movement), and the fourth is REM sleep (rapid eye movement).

During the NREM stages, the body gradually moves into deeper sleep. Heart rate slows, muscles relax, and brain activity winds down. The deepest stage, NREM3, is especially important for physical restoration and immune function. You can dream during NREM stages too, but these dreams tend to be more fragmented and less vivid than what you experience during REM.

REM sleep is where the most intense dreams play out. The eyes move rapidly behind closed lids, brain activity increases dramatically, and the body becomes temporarily paralysed — a phenomenon called muscle atonia. This paralysis stops you from physically acting out what you’re dreaming. The first REM periods of the night are short, maybe just ten minutes, but by morning they can last up to an hour. That’s why you’re more likely to remember dreams when you wake up in the morning.

Why do we dream? Three leading theories

Science hasn’t settled on one final explanation, but there are several theories, each shedding light on a different side of dreaming.

Memory consolidation is perhaps the most well-supported theory in modern research. During sleep, and especially REM sleep, the brain processes the day’s experiences. It sorts out what’s important enough to store in long-term memory and lets the rest slip away. Studies have shown that people who sleep well after learning something new retain it better than those kept awake. Dreams may be a byproduct of this sorting process — or perhaps an active part of it.

Emotional regulation is another central theory. Neuroscientist Matthew Walker has described REM sleep as a form of overnight therapy. While dreaming, the brain relives emotional situations, but in a chemical environment with lower levels of the stress hormone noradrenaline. This may make it possible to process difficult experiences without the same physiological stress response you’d have while awake. It could explain why sleep deprivation often leads to heightened emotional reactivity and irritability.

Threat simulation is an evolutionary theory proposed by Finnish researcher Antti Revonsuo. According to this theory, dreams function as a kind of training ground where the brain rehearses dangerous or challenging situations. Dreams of falling, being chased, or facing a threatening snake may be the brain’s way of preparing us for real dangers. This theory can explain why so many dreams carry negative or threatening content.

Freud, Jung and the hidden meaning of dreams

Long before neuroscience turned its attention to dreams, psychology tried to make sense of them. The two most influential thinkers in the field are Sigmund Freud and Carl Gustav Jung.

Freud published The Interpretation of Dreams in 1900 and called dreaming “the royal road to the unconscious.” He believed dreams were the disguised fulfilment of repressed wishes, particularly those tied to sexuality and childhood experiences. According to Freud, dreams had a manifest content — what you actually see and experience — and a latent content — the underlying, hidden meaning. A dream about a house might really be about the self, and a dark room about something you didn’t want to confront.

Jung, originally Freud’s student, developed a different perspective. He believed dreams don’t primarily conceal, but reveal. They’re the brain’s attempt to communicate important information to the conscious part of the mind. Jung introduced the idea of archetypes — universal symbols that recur across cultures. Dreams of water could represent the unconscious, while dreams of a wolf could point to instinctive forces.

Modern psychology has moved away from many of Freud’s specific theories, but the idea that dreams can reflect emotional states and unconscious processes has survived. Jung’s archetypal approach has also proven useful as a tool for self-reflection, even if it isn’t necessarily provable in a strict scientific sense.

What modern neuroscience tells us

The past few decades have given us entirely new tools for studying dreams. Functional MRI (fMRI) and EEG make it possible to observe brain activity in real time during sleep.

Research shows that dreaming activates many of the same brain regions as waking experience. The visual cortex is active, which explains the vivid imagery. The amygdala, the brain’s emotional centre, is highly active during REM sleep, which may explain the intense emotional charge in many dreams. The prefrontal cortex, responsible for logical thinking and self-control, is meanwhile less active. This is likely why dreams often lack logic — you accept strange events without question.

One fascinating area of research is how dream content connects to daily experience. Studies have shown that what you experience during the day often shows up in dreams, but rarely directly. Daytime experiences can be woven into new scenarios, combined with memories from weeks or years earlier. This creative recombination may be part of the brain’s problem-solving strategy.

There’s also research suggesting dreams can contribute to creativity. Many well-known scientific and artistic breakthroughs have been credited to dreams. It’s hard to prove a direct causal link, but the unique combinations the brain creates during dream sleep can certainly provide fertile ground for new ideas and perspectives.

Do we all dream the same way?

A common question is whether everyone dreams the same things. The answer is both yes and no. Certain dream motifs recur across cultures: dreams of falling, being naked in a public place, or losing teeth are reported by people all over the world. That suggests some dream motifs may have universal roots, whether biological or psychological.

At the same time, dreams are shaped by individual experience, culture and life circumstances. Someone who lives near the sea might dream more often of waves and ocean, while someone who has just had a baby might dream about babies. Studies also suggest that blind people dream using other senses than sight — experiencing sound, touch and smell in their dreams.

Age plays a role too. Children often have more imaginative dreams involving animals and fantastical scenarios, while adults more often dream about social situations, work and relationships. Older adults generally report fewer nightmares than younger adults, which may be linked to improved emotional regulation over time.

What we still don’t know

• Dreams occur in every sleep stage, but are most intense and vivid during REM sleep.
• Science points to memory consolidation, emotional regulation and threat simulation as central functions.
• Freud and Jung laid the groundwork for psychological dream interpretation, but modern neuroscience has broadened and refined our understanding.
• Some dream motifs are universal, while others are shaped by personal experience and culture.
• There’s still a great deal we don’t know — and that’s perhaps part of what makes dreams so fascinating.

Whatever science eventually concludes, dreams invite us to get to know ourselves better. Paying attention to what you dream about can be a valuable form of self-reflection.

Sources and further reading

• Sigmund Freud, The Interpretation of Dreams (1900) — the wish-fulfilment theory, and the starting point for all modern dream interpretation, including the theories that disagree with him.
• Carl Gustav Jung, Man and His Symbols (1964) — archetypes, the collective unconscious, and the break with Freud.
• G. William Domhoff, The Scientific Study of Dreams (2003) — the continuity hypothesis and the empirical challenge to hidden symbolism.
• Matthew Walker, Why We Sleep (2017) — the neurobiology of REM sleep and the role of dreams in emotional regulation.