[The concept of biological rhythm in psychopathology]

The chronobiological hypotheses of depression are based on epidemiological, biological as well as therapeutical pieces of evidence. The seasonal pattern of depression and suicide rates tend to link affective disorders and the daylight duration. Disturbances of circadian rhythms have been reported in endogenous depression. Treatments of depression, such as manipulations of the sleep/wake cycle, phototherapy or tricyclics, may involve chronobiological mechanisms on endogenous pacemakers. Beside the phase advance hypothesis of depression, present data seem to involve a disturbance of the mechanisms of entrainment of the internal clocks by external synchronizers. Other psychiatric illnesses may thus be linked to chronobiological abnormalities.