FIG. 5. The relationship between mood regulation and the circadian system. The circadian clock affects several systems and pathways which are supposedly the cause of mood disorders. In the majority of patients there are shared aberrant connections which lead to dysregulated daily oscillations. Circadian gene mutations possibly make a person more susceptible to affective disturbances and these are worsened by environmental variations in the daily timetable. 5-HT: 5-hydroxytryptamine, DA: dopamine, HPA-axis: hypothalamic pituitary axis, NA: norepinephrine, SCN: supraschiasmatic nucleus.