It sounds like something out of a science fiction movie about making supersoldiers. Scientists have turned shy, low-ranking mice into aggressive fighters who almost always win in dominance competitions. And they did it by stimulating a part of the mouse brain that controls “effortful” behavior.

Mice are social animals, and male mice establish a pecking order amongst themselves by displaying aggressive behavior. Though this aggression can take many forms, neuroscientist Zhou Tingting of the Chinese Academy of Sciences, Shanghai, joined with his colleagues to measure mouse dominance using what’s called the “tube test.” The tube test creates a scenario in which there’s not enough room for the mice to pass each other in the tube. Mice have to shove one another aside to get out. The mouse who shoves the most other mice out of its way will “win” the dominance game.