CIRCADIAN-RHYTHMS OF EARLY-MORNING AWAKENING INSOMNIACS

It has been suggested that two types of insomnia, sleep onset insomnia and early morning awakening insomnia, may be caused by delays and adv ances respectively of circadian rhythms. Evidence supports the circadi an rhythm phase delay of sleep onset insomniacs. The present study inv estigated the phase timing of circadian rhythms of early morning awake ning insomniacs compared with a group of age matched good sleepers. A 24-h bed rest laboratory session was used to evaluate the endogenous c ore body temperature and urinary melatonin rhythms. Objective and subj ective sleepiness were also measured every 30 min across the session w ith 10 min multiple sleep latency tests and Stanford Sleepiness Scale. Maximum and minimum phases of each individual's rhythm were identifie d using two-component cosine curve fitting. Compared with the good sle epers, the insomniacs had significant phase advances of 2-4 h for the temperature and melatonin rhythms. However, the 0-4 h advances of the sleepiness rhythms were not significant. This latter unexpected result was explained on the basis of variability of sleepiness measures. It was suggested that early morning awakening insomnia arises from phase advanced circadian rhythms which evoke early arousal's from sleep.