Circadian Rhythm Mechanisms in Affective Illness and in Antidepressant Drug Action

A number of circadian rhythms (e.g. body temperature, REM sleep, cortisol) appear to be abnormally phase-advanced in depression. Partial sleep deprivation in the second half of the night and phase-advance of the sleep-wake cycle induce temporary clinical remission: these experiments indicate that abnormally advanced rhythms are not merely an epiphenomenon but play an important role in the pathogenesis of depression. They lead to the hypothesis that depression occurs in susceptible individuals when a sleep-sensitive phase of the circadian system becomes advanced from the first hours of waking into the last hours of sleep and interacts with sleep to cause depression.