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phase advance

(advanced sleep phase syndrome)
The shift of an episode of sleep or wake to an earlier position in the 24-hour sleep-wake cycle. A shift of sleep from 11 P.M. to 7 A.M. to 8 P.M. to 4 A.M. represents a 3-hour phase advance. See phase delay.

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