In addition, PET imaging for translocator protein (TSPO), a marker of microglia, has revealed a significantly attenuated microgliosis in the prefrontal cortex of PTSD patients compared to subjects non-exposed to trauma, and more importantly, a negative correlation between TSPO availability and symptome severity, suggesting brain immune deficiency as the underlying mechanism of PTSD [431]. Here, TSPO is linked to post-traumatic stress disorder.