Rapid eye movement (REM) is a stage of sleep characterized by fast, random eye movements and vivid dreams. Synonyms for REM include paradoxical sleep, desynchronized sleep, and active sleep. Paradoxical sleep describes the phenomenon of the brain appearing awake while the body remains still, leading to dreams and muscle atonia. Desynchronized sleep refers to the erratic electrical activity of the brain during REM, while active sleep focuses on the heightened metabolic and respiration rates during this stage. Additional synonyms for REM can include dreaming sleep and neurogenic sleep, emphasizing the role that this stage plays in cognitive and neuronal processing.