Brain imaging has identified numerous regions of altered structure or activity in the brain during major depression, suggesting disordered neurocircuitry in a variety of structures, such as the anterior and posterior cingulate cortex; the ventral, medial, and dorsolateral prefrontal cortex; the insula; the ventral striatum; the hippocampus; the medial thalamus; the amygdala; and the brain stem. These brain areas regulate emotional, cognitive, autonomic, sleep, and stress-response behaviors that are impaired in mood disorders. Studies with the use of positron-emission tomography indicate a decrease in serotonin transporters as well as altered postsynaptic serotonin-receptor binding in many of the same brain regions, suggesting altered circuitry congruent with serotonin-system abnormalities