Composite PET (positron emission tomography) scan data, superimposed on MRI (magnetic resonance imaging) scans, show brain areas that increased (red) or decreased (yellow) in activity in men who responded to placebo (top row) and fluoxetine (bottom row). Both groups shared a pattern of increased activity in the cortex (e.g., prefrontal, posterior cingulate) and decreased activity in limbic regions (e.g., subgenual cingulate), which the researchers suggest is necessary for therapeutic response. Men who responded to the active medication, in addition, experienced decreased activity in certain lower brain areas (e.g., hippocampus, anterior insula) thought to sustain the cortical/limbic changes and prevent relapse.

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