Microglia are critical modulators of neuronal activity, regulating brain function through removal of dying neurons, pruning non-functional synapses, and producing ligands that support neuronal survival. Microglial morphologies change with aging, shifting from a homeostatic, surveillant state (ramified morphology) to a more reactive state (intermediate, amoeboid, and dystrophic morphology). Common marmosets ( Callithrix jacchus...