Using 11C-harmine PET, independent studies have identified a significant increase (13–22%) in MAOA density in the ACC and prefrontal cortex (PFC) of PPD patients [54], and a 34% average increase in the ACC, PFC, hippocampus, thalamus, caudate, putamen, midbrain, and anterior temporal cortex of MDD patients [55]. Here, MAOA is linked to major depressive disorder.