Why do we dream?

Some hunt criminals or fight monsters, others fly through the universe or have superpowers. Everything is possible in a dream. But why does the brain produce so many colorful films every night?

Dreams are part of sleep. And if you don’t remember the nightly experiences the next day, you still had them. But why do we dream at all? Is there a deeper meaning behind this?

Many dreams seem like a colorful hodgepodge of disjointed scenes – a senseless sequence of experiences, impressions and feelings. For over 100 years, psychologists and neuroscientists have wanted to explore the world of thought while sleeping. But that is still difficult, not only because of the lack of dream logic, but above all because communication with the sleeper is usually not possible.

In order to catch a glimpse behind this curtain, researchers combine a wide variety of measurements. During such a polysomnography, a number of other behavioral and physiological parameters are recorded at the same time as an EEG – the brain waves tapped from the skull – including eye movements, muscle tone, heart rhythm and respiratory volume as well as movements of the fingers and limbs. More than 50 years ago it turned out that the individual sleep cycles consist roughly of two different phases: of sections with rather slow, large brain waves, which in turn are divided into several light and deep sleep stages; and episodes of so-called paradoxical sleep with fast, low waves, which is also called REM sleep (rapid eye movements) because of the rapid eye movements that occur. The sections with slow waves, on the other hand, are called non-REM, NREM or orthodox sleep. At first it was said that dreams only occur during paradoxical sleep. That has long been refuted.