Sometimes, all that mice do is win.
Other times, they win so much they get sick and tired of winning.
Now, scientists have figured out how to reach inside a mouse’s brain and flick a neuronal switch that triggers them to either become alpha males who excel at aggressive encounters — or become more likely to retreat.
A team of researchers in China identified a circuit in the brain that plays a strong role in social dominance in mice, and were able to activate the region — known as the dorsomedial prefrontal cortex — by hitting it with light beams.
“We can change the dominance behavior very quickly by changing the activity of this one particular brain area,” said Hailan Hu, the study’s senior principle investigator and a professor at Zhejiang University in China. “It does so without changing the physical strength or aggression level of the animals.”
Many animals engage in complex forms of competitive rituals to create intricate structures of social hierarchy. Researchers who study the process have observed a phenomenon called the "winner effect,” in which each victory over a peer increases the odds of winning the next social dominance showdown.
The researchers in China constructed a standardized competition that pitted male mice against each other inside a tube facing each other.
The researchers then recorded how much each one engaged in a range of behaviors: initiating a push against their opponent, pushing back, resistance, retreat, or stillness.
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Brain monitoring revealed that a particular subset of neurons in the brain area they were looking at became more active during so-called “dominant” behaviors of pushing and resistance in the contest.
Next, the scientists took mice that had already established a social rank, and gave them drugs that inhibited the functioning of this subset of neurons. Within hours, the drugged mice engaged in fewer and less vigorous pushes and push-backs — and retreated more often.
Then, when researchers used optogenetics to stimulate the brain area with light during a social dominance encounter, the stimulated mice achieved a 90 percent success rate over other previously dominant mice, without affecting the motor performance or anxiety level of the animal receiving the light treatment.
The team published their findings today in the journal Science.
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So would the technique work on people?
Hu said she thinks it might, although research would be required to be sure. An analogous circuit is thought to operate in a comparable way in human brains, Hu said.
“A similar circuit exists, but whether it plays the same role remains to be tested,” she said. “Studies have shown there’s changed activity in this area in the prefrontal cortex during dominance-related behavior.”
“I can only say at this point that it’s likely,” Hu said.