A brain implant turns “loser” mice into aggressive fighters

Enlarge / Could this be the first step toward the Mouse Guard from David Petersen’s amazing comic book?

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.

Mice shove each other in the tube test. Note that the winner isn’t stronger—he’s just more aggressive and persistent with his shoves.

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.

Zhou and his colleagues wondered whether they could create “winner” mice by stimulating the dmPFC. Using a brain stimulation technique called “optogenetics” that triggers neural activity with proteins and light, they stimulated the dmPFC region of a low-ranking mouse’s brain. Then the low-ranking mouse took the tube test with a…

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