Humans, monkeys and chimpanzees have a default-mode network (DMN); that is, functionally connected brain areas that become less active during cognitive tasks. Lu et al. now show that among several resting-state networks in anaesthetized rats, one network is broadly similar to the human DMN. The organization of this network, with two subsystems centred around the prefrontal cortex and the retrosplenial cortex, respectively, is also similar (although not identical) to that in humans. These findings suggest that a DMN may be a fundamental aspect of the mammalian brain.