Serotonergic mechanisms can be investigated by experimental manipulations via drug challenges or by systematic variations of serotonergic genotypes. Both interventions should however converge on common mechanisms underlying human affective or cognitive processing or their deviation in depressive disorders. Alterations and variations of brain circuitry will be discussed as revealed by means of non-invasive fMRI studies in humans. Activations of brain regions and entire networks during explicit task paradigms will be compared to changes of brain network circuitry during resting state conditions.

This perspective shall shed light on the complex interaction of brain and environment during serontonergic modulation of social behavior.