What’s the purpose of dreaming?

3 3 minutes read

We all dream — but why? As with many mysteries of the mind, science doesn’t have one neat answer.

“You’ll get as many answers to the question ‘What is the purpose of dreaming?’ as there are dream psychologists,” says Deirdre Barrett, dream researcher at Harvard University and author of The Committee of Sleep.

According to Austrian neurologist and founder of psychoanalysis Sigmund Freud, dreams offered vital clues to unresolved conflicts buried deep within our psyche. But Freud’s theory, introduced in his 1899 book The Interpretation of Dreams, sparked plenty of controversy. Critics argued that his dream interpretations were overly focused on sex, highly subjective, and impossible to verify—two analysts might offer entirely different readings of the same dream, with no objective way to know who was right.

In the decades since Freud, other scientists have offered alternative explanations for why we dream. One of the most prominent is the threat simulation theory, proposed by Finnish neuroscientist and psychologist Antti Revonsuo in 2000. According to this view, dreaming is an ancient biological defense mechanism. By simulating dangerous situations, our brains rehearse the skills needed to recognize and avoid threats—a kind of virtual reality training ground for survival. A 2005 study lent support to this theory by examining the dreams of Kurdish children exposed to war and trauma. Compared to non-traumatized Finnish children, these children reported more frequent dreams filled with severe threats, suggesting that their minds were practicing how to cope with danger.

But even the threat simulation theory is debated. A 2008 study comparing residents of high-crime areas in South Africa to those in low-crime parts of Wales found that South African participants, despite facing more real-world threats, actually reported fewer threatening dreams than their Welsh counterparts. This result challenges the idea that the brain uses dreams to simulate danger when exposed to trauma.

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Another theory suggests that dreams are simply a side effect of memory consolidation—the brain’s way of replaying and reinforcing new memories while we sleep. As the brain’s hippocampus and neocortex work together to file away fresh information, they may also blend it with older memories, creating the often strange mashups we experience as dreams.

Dreams may also help us process and manage emotions, especially negative ones, according to the emotion regulation theory of dreaming. Research focusing on recently divorced individuals experiencing depression found that participants who dreamed about their ex-spouses were more likely to show significant improvement in their mood one year later, particularly if their dreams were vivid and emotionally rich. Another study found that people who dreamed about stressful events they had experienced before sleep woke up feeling more positively about the events the next day, suggesting that dreams can help transform emotional distress into resilience.

Recent brain imaging studies support this idea. People who frequently experience fear-related dreams show reduced activation in fear centers of the brain during waking life, hinting that these dreams may serve as a kind of overnight therapy session, helping us better regulate our emotions when awake.

Ultimately, Barrett suggests that we may be asking the wrong question. “We’d rarely ask the analogous question: ‘What is the purpose of thinking?’” she says. Just as waking thought serves many functions—from planning to problem-solving to daydreaming—dreams likely do too. “The value of dreaming lies in its difference. It’s a distinct mode of thought—one that supplements and enriches our waking cognition.”

In fact, some researchers believe dreams offer a unique mental space for solving problems that stump us during the day. In this altered brain state, regions responsible for imagery become more active, allowing the mind to solve problems requiring visualisation. History is full of famous examples: Mary Shelley reportedly dreamed the central scenes of Frankenstein; German chemist August Kekulé envisioned the ring structure of benzene in a dream; and Russian chemist Dmitri Mendeleev dreamed his final form of the periodic table of the elements.

In the end, dreams may serve many purposes—or none at all—but they remind us that even in sleep, the brain never truly rests.

This story is part of Popular Science’s Ask Us Anything series, where we answer your most outlandish, mind-burning questions, from the ordinary to the off-the-wall. Have something you’ve always wanted to know? Ask us.