If you're reaching for the last piece of pizza at a party, and meanwhile see another hand going for it, your next move probably depends on how you feel and whom the hand belongs to. Your little sister — you might just grab the pizza. Your boss — you probably will give up.
Now researchers have made progress in understanding how mammals' brain encodes social rank and uses this information to shape behaviors — such as whether to fight for the last pizza slice. They discovered that an area of the brain called the medial prefrontal cortex (mPFC) was responsible for representing social rank in mammals; changes to a mouse's mPFC affected its dominance behavior. But it was unknown how the mPFC represented this information and which neurons(神经元) were involved in changing dominance behaviour.
In the new study, Professor Kay Tye let groups of four mice share a cage. Some mice became more dominant and others more subordinate. As soon as the mice were paired up, he discovered, the activity of their mPFC neurons could predict — with 90 percent certainty — the rank of their opponent.
"We expected animals might only signal rank when they are in a competition," says co-researcher Nancy. "But it turns out animals walk around with this representation of social rank all the time."
When the researchers next asked whether the activity of the mPFC neurons was associated with behaviour, they found something surprising. The brain activity patterns were linked with slight changes in behaviour, such as how fast a mouse moved, and they also could predict — a full 30 seconds before the competition started — which mouse would win the food reward.
The winner was not always the more dominant, but the one engaged in a winning mindset. Just as you might sometimes be in a more competitive mood and be more likely to snatch that pizza slice before your boss, a subordinate mouse might be in a more winning mindset than a more dominant mouse and end up winning.
The areas of the mPFC associated with social rank and winning mindset are next to one another and highly connected. Signals on social rank impact the state of the brain involved in winning mindset. In other words, a subordinate mouse's confidence and winning mindset may partially decrease when faced with a dominant one.
"This is further evidence to suggest that we are in different brain states when we are with others compared to when we're alone," says Tye.
