[Biological rhythms and depression].

Circadian rhythms are found in all living organisms, and represent a physiological correlate of the geophysical rhythm of day and night. These rhythms are endogenous in nature, driven by a pacemaker in the hypothalamus, and synchronized to the 24-hour day. Many of the symptoms of affective illness can be considered in terms of altered timing of circadian rhythms. Furthermore, total or partial sleep deprivation or phase advance of the sleep-wake cycle can induce remission (albeit temporary) in many depressive patients, and antidepressant drugs influence circadian rhythm characteristics. Bright light may have antidepressant properties in certain seasonally recurring depressives.