It’s an endlessly fascinating question, one pondered by artists, philosophers, scientists, and everyday dreamers throughout human history. Dreaming is a universal human experience, one of the most mysterious and engaging aspects of our sleeping lives.

Dreaming experiences vary widely. Some dreams are thrilling, while others are frightening. Some reflect experiences of our daily lives, with characters, places, and events that are recognizable. Other dreams venture into bizarre, and seemingly unfamiliar terrain. There are several different types of dreams, including:

  • Nightmares. Most of us experience nightmares at some point. These are frightening dreams that usually result in waking the dreamer from sleep, at least briefly.
  • Sleep terrors (also known as night terrors). Distinct from nightmares, sleep terrors are intense periods of fright during sleep. They may be accompanied by screams, agitated movements, or jumping from bed. Night terrors are more common in children than adults.
  • Recurring dreams. These are dreams that, over time, return again and again for the dreamer.
  • Lucid dreams. These striking dreams are ones in which the dreamer, though sleeping, is aware he is dreaming, and may be able to control some aspects of the dream.At a fundamental level, all dreams are collections of emotions, events, images, and impressions that we experience during sleep.

Dreaming 101

Most dreams go unremembered, or forgotten within moments of waking after a night of sleep. But our limited ability to recall dreams is not an indication of how much time we spend dreaming. Dreaming is a routine, nightly part of sleep. Typically, a person will spend two hours or more every night dreaming, covering anywhere between three to six different dreams over the course of a single night’s sleep. Individual dreams usually last from 5-20 minutes.

Though dreaming can occur during any of the four stages of sleep, REM sleep is a nightly sleep phase when a flurry of dreaming occurs. During REM sleep, the brain is highly active—brain activity in REM sleep looks very similar to the activity of a waking brain.

Investigating the Why of Dreams

For all the attention dreams have received, we actually know little about the true purpose of dreaming. The content of dreams has been analyzed and interpreted by humans for millennia. In the late 19th and early 20th centuries, dreams were vigorously studies by physicians, like Sigmund Freud and Carl Jung, seeking to understand the human psyche.

By the 1950s, scientists were beginning to explore the neurological aspects of dreaming, enabled by new EEG technology that allowed scientists for the first time to observe the activity of the brain during sleep. Since then, rigorous and increasingly illuminating scientific investigations of dreams and sleep have put forth many theories about why we dream. But no definitive answer exists. Scientists studying the characteristics, mechanics, and purpose of dreaming hypothesize that dreams may be:

  • A continuation of waking consciousness
  • A mechanism for processing memory and learning that occurs during the waking day
  • A way for the mind to maintain emotional and psychological equilibrium, by working through difficult, frightening, stressful, and emotional experiences
  • The brain’s organizing response to biochemical changes and electrical impulses that transpire during sleep
  • A kind of virtual reality that allows the brain to rehearse situations and test scenarios in order to prepare itself for challenges and threats in waking life

Whatever we learn in the future from the scientific study of sleep and dreams, it seems likely the answer to the question why do we dream won’t be a simple one. Dreams themselves are complex and dynamic, and their function may be multi-purpose, serving biological, psychological, and cognitive needs all at once.

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