In the healthy adult brain microglia, the main im­mune-com­pe­tent cells of the CNS, have a dis­tinct (so-called “rest­ing”, see image) phe­notype. Rest­ing microglia can only be stud­ied in vivo since any isolation of brain tissue inevitably trig­gers microglial activation. Us­ing in vivo two-photon imag­ing we obtained a first di­rect in­sight into Ca²⁺ signaling in rest­ing cortical microglia.