Clinical parameters of circadian rhythms in affective disorders

Many affective disorders show episode cycling and the classic symptoms of these disorders show rhythmicity, such as diurnal variation in mood. There are several plausible stress–vulnerability models that suggest links between these observed phenomena and the circadian system. For example, an individual with increased sensitivity to social rhythm disruption may be more at risk of circadian rhythm (CR) dysregulation. Furthermore, there are hypothesized neurobiological mechanisms that may explain how CR dysregulation might lead to sleep, activation, and mood changes in unipolar and bipolar disorders. There are gaps in our understanding, but this paper highlights that clinical measures of sleep and activation are increasingly useful for monitoring the onset and course of affective disorders. Also, evidence suggests that CR disruptions may represent core elements not simply epiphenomena of affective disorders.