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non-REM-REM sleep cycle

A period during sleep composed of a non-REM sleep episode and the subsequent REM sleep episode; each non-REM-REM sleep couplet is equal to one cycle. Any non-REM sleep stage suffices as the non-REM sleep portion of a cycle. An adult sleep period of 6.5-8.5 hours generally consists of four to six cycles. The cycle duration increases from infancy to young adulthood. (synonymous with non-REM-REM sleep cycle)

Definition reprinted with permission from Culebras, Antonio, Clinical Handbook of Sleep Disorders, Butterworth-Heinemann