FREE-RUNNING OF PLASMA MELATONIN RHYTHM PRIOR TO LULL MANIFESTATION OF A NON-24 HOUR SLEEP-WAKE SYNDROME

A long-term observation of a sighted man who developed a non-24 h slee p-wake syndrome is reported. A partial entrainment was observed first, whereby the sleep-wake rhythm was entrained by the day-night alternat ion whereas the circadian rhythm in plasma melatonin was free-running. Two years later, the sleep-wake rhythm of this subject started to fre e-run together with the melatonin rhythm. Oral administration of melat onin for 2 weeks improved the entrainability of both rhythms but faile d to entrain the rhythms completely. It is concluded that the free-run ning of the circadian pacemaker preceded a full manifestation of a non -24 h sleep-wake syndrome in this particular subject.