TSPO and psychiatric disorder: We analyzed the hippocampal and the substantia nigra regions since these are the most densely microglia populated areas of the brain (De Biase et al., 2017, Tan et al., 2020) and because several clinical studies have demonstrated changes in TSPO PET signal in these areas of patients with neurodegenerative and psychiatric disorders (Haarman et al., 2014, Kreisl et al., 2016, Ouchi et al., 2005).