The Brain

Triggering Neural Circuit Instills Dominance In Mice

We don’t want to give credibility to those awful guides on how to achieve social dominance, but it seems that, in mice at least, being top of the pecking order is all in the mind. A neural circuit in the rodent brain controls social dominance – when it’s stimulated, a mouse can rise to the top of the social tree, even when its opponent would otherwise win.

Confidence can certainly take you far. We’ve all met people who make up in self-belief what they lack in talent, and seem to do very well out of it. In the animal kingdom, this has been measured in what is called the “winner effect”. An animal that wins one show-down for social dominance is more likely to triumph again, even if its first victory was built on luck or having a weak opponent, not merit. Success really does breed success.

A team from leading Chinese universities scanned the brains of mice in conflict and observed firing in the dorsomedial prefrontal cortex (dmPFC). They decided to test whether stimulating or depressing the dmPFC with bursts of light could alter the outcome of head-to-head encounters between mice in transparent tubes.

Senior author Professor Hailan Hu of the Zhejiang University reported in Science that, “activation or inhibition of the dmPFC induces instant winning or losing, respectively.” Mice that had their dmPFC activated won 90 percent of contests, even against opponents that had previously beaten them.

Mice whose dmPFC had been stimulated pushed harder, longer, and more frequently when encountering another mouse, eventually forcing their counterparts to back off and exit the tube. Success in the tube was transferable to contests over a desirable warm spot too.

Mice with the misfortune to encounter a stimulated opponent usually ended up vacating the field. Zhou et al/Science

The mouse dmPFC is small – just 342 neurons – yet still showed specialization, with different, albeit overlapping, neurons firing when mice were pushing verse when they were resisting being pushed.

Exactly how the dmPFC works its magic remains unclear. It does not, for example, change muscle strength, as measured by grip. Nor did the stimulated mice show increased aggressive behavior in terms of attacking or chasing other mice. Instead, it seems stimulation caused mice to try harder at activity they would have undertaken anyway.

Intriguing differences were observed in how long the stimulation lasted. By the second day after stimulation, “some mice returned to their original rank, whereas others maintained their original rank,” the authors report. The mice that showed a sustained benefit had experienced at least six wins on the first day, whereas those with five or fewer wins saw their dominance fade. This had more to do with the opponents they were up against than the subjects’ internal capacities. Consequently, the authors conclude “repeated stimulated winning led to sustained dominance.”

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