What Happens in the Brain When You’re Dreaming
The brain does something special during sleep. Instead of simply switching off, it activates patterns of activity that can lead to dreaming. But what exactly is happening to the brain during a dream? It’s a question that has puzzled scientists for a long time, and new research is revealing some answers.
In the sleeping brain, there are two major states: rapid eye movement (REM) and non-REM. Non-REM is split into separate stages, each occupying a progressively deeper phase of sleep. The first and lightest stage of non-REM sleep features slow eye movements and brain waves at a relatively high frequency of around 4 to 7 Hz. On the other end of the spectrum, the deepest stage of non-REM sleep is commonly referred to as slow-wave sleep, and features brain waves at lower frequencies (less than 4 Hz). During this deep stage, the brain is minimally reactive to external sounds, and people are less likely to wake up.
As its name suggests, one of the most distinctive features of REM sleep is that people exhibit quick and jerky eye movements. REM is not the only time people dream, but it does seem to be when people experience the longest, most vivid, and most bizarre dreams. In a bid to stop people from acting out these dreams while asleep, the brain inhibits motor systems to reduce muscle action or even paralyze muscles. People commonly experience this paralysis during nightmares when they try to run but their legs feel powerless.
In a 2017 study, researchers tested whether brain activity during REM and non-REM sleep would predict what happened in people’s dreams. The researchers woke people up at various intervals during the night and asked them to describe any dreams they were having. The researchers also measured the strength of people’s slow brain waves. For both REM and non-REM sleep, people were more likely to report having a dream when brain waves were weak. When they were stronger, the men and women in the study were more likely to report feeling unconscious with no dream experiences whatsoever.
Dreams can feature all kinds of physical feelings and sensations that occur in the real world. When people experience those sensations during REM sleep, the brain recruits some of the…