PET ligands for the translocator protein (TSPO), such as [11C]PK11195, have revealed increased microglial activation in frontotemporal regions in patients with both sporadic and genetic FTD.14–18 [11C]PK11195 PET indicates differential regional activation of microglia according to clinical phenotype14,15 and genetic variant.17 The PET studies are complemented by post-mortem evidence of elevated microglial activation in frontal and temporal regions.6,7,15. Here, TSPO is linked to frontotemporal dementia.