Which sleep stage is characterized by rapid eye movement?

The stage characterized by rapid eye movement is REM (Rapid Eye Movement) sleep. During this stage of sleep, the brain is highly active, resembling a waking state, and most vivid dreaming occurs. The rapid movements of the eyes are a defining feature, and this stage is crucial for cognitive functions such as memory consolidation and emotional regulation.

In contrast, other stages of sleep, such as N1, N3, and N4, do not exhibit rapid eye movements. N1 is a light sleep stage where a person may be easily awakened, N3 (also referred to as deep or slow-wave sleep) features delta brain waves and is essential for physical restoration, and N4 is another designation (though N3 and N4 are often combined as deep sleep). Therefore, the unique presence of rapid eye movement in REM sleep is vital for distinguishing it from the other stages.