Sleep Cycles

Abstract Human sleep changes across the night in a cyclic pattern. Each sleep cycle begins with non‐rapid eye movement (NREM) sleep and ends with rapid eye movement (REM) sleep. The cycling frequency is approximately 90 minutes but shorter than this during the first year of life. The number of sleep cycles depends on the duration of sleep. An average young adult who sleeps well has between 5 and 6 sleep cycles during a typical night's sleep. The organization of sleep during the first year of life differs substantially and depends on brain maturation during this early stage of human development.