Neuroimaging studies using positron emission tomography (PET), often combined with computed tomography (CT) or magnetic resonance imaging (MRI), have identified increased expression of the translocator protein (TSPO)—a marker of microglial activation—in the prefrontal cortex, anterior cingulate cortex, insula, and hippocampus of individuals with depression (103, 104). This evidence concerns the gene TSPO and depressive symptom measurement.