朝活ミニテスト 第30回

Why We Dream

Although humans spend roughly a third of their lives asleep, the purpose of dreaming remains one of the great unsolved puzzles of science. Most vivid dreams occur during rapid eye movement, or REM, sleep, a stage in which the brain is nearly as active as when we are awake, while most of the body's muscles are temporarily paralyzed. For much of the twentieth century, some scientists argued that dreams had no real purpose at all. According to this view, dreams are merely a by-product of random signals generated in the brainstem during sleep, which the higher regions of the brain then try to weave into a story.

More recent research, however, has led many scientists to suspect that dreaming does serve a function. One influential theory holds that it helps people process emotional memories. During REM sleep, levels of certain stress-related chemicals in the brain are thought to be unusually low, allowing upsetting experiences to be replayed in a relatively calm state. Over time, this may gradually reduce their emotional impact. Supporting this idea, some studies have found that people deprived of REM sleep tend to react more strongly to negative images the following day.

Another theory proposes that dreams act as a kind of simulation, allowing the brain to rehearse responses to threats without facing real danger. Supporters point out that dreams of being chased or falling are reported across many cultures, which would be expected if dreaming had evolved to prepare humans for challenges. Critics note that many dreams are mundane or bizarre rather than threatening. Nevertheless, these explanations are not necessarily incompatible, and many researchers now suspect that dreaming may serve more than one purpose, much as sleep itself supports numerous bodily functions.