Which sleep stage is characterized by rapid eye movement?

REM (Rapid Eye Movement) sleep is characterized by the distinct rapid eye movements that occur during this stage. It's a phase of sleep that is crucial for various functions, including memory consolidation and emotional regulation. During REM sleep, brain activity becomes similar to that of wakefulness, which is why this stage is deeply linked to dreaming. The physiological features associated with REM sleep include increased brain activity, muscle atonia (temporary paralysis of most voluntary muscles), and variations in heart rate and breathing patterns.

Other stages mentioned, such as NREM sleep (which encompasses stages 1, 2, and 3), do not exhibit these rapid eye movements. Stage 3 NREM sleep, or deep sleep, is particularly important for physical restoration and does not involve the characteristics of REM sleep. Stage 1 is the transition from wakefulness to sleep, marked by a decrease in muscle activity and theta waves in the brain but also lacks the defining rapid eye movements of REM. Recognizing these distinctions is crucial for understanding sleep architecture and the overall sleep cycle.