In a recent article for Science, Zhou and his colleagues write that "winner mice initiated significantly more pushes, and with a longer duration per push, than loser mice." Winners weren't stronger than losers; they were simply more persistently aggressive. The researchers also found that the winner mice showed brain activity in a cluster of neurons called the dorsomedial prefrontal cortex (dmPFC), which is associated with "effortful behavior" and "social dominance." Mice whose dmPFC was quiet during tube tests always lost.