Many species in the animal kingdom compete with each other to form a system of social hierarchy. From this hierarchy, a phenomenon called the "winner effect" has been observed, whereby each victory against a peer increases the victor's probability of winning the next social dominance showdown.

Researchers have identified a neural circuit in the brains of mice that plays a role in social dominance. Stimulating the neurons in this circuit significantly boosted a mouse's chance of becoming the "winner" during aggressive encounters with other mice.

The dorsomedial prefrontal cortex (dmPFC) has been implicated in the long-term regulation of social dominance, yet the exact mechanism behind the "winner effect" remains unknown. To gain more insights into the effect's molecular underpinnings, researcehres studied mice as they performed a standard social dominance test.

In this test, male mice in a tube face each other and researchers record how much each one engages in certain behaviors: push initiation, push-back, resistance, retreat, or stillness. Here, monitoring individual neurons in the dmPFC during such tests revealed that a particular subset became more active during both push and resistance (or dominance) behaviors.

In mice with an established social rank, the researchers inhibited this subset of dominance neurons using a drug; within hours, these mice engaged in significantly fewer and shorter pushes and push-backs, the authors say, and in more retreats.

Next the researchers used optogenetics to stimulate the dmPFC neurons continuously during a social dominance encounter. This instantaneously induced winning against previously dominant opponents with a 90% success rate, without affecting the motor performance or anxiety level.

Remarkably, stimulating these neurons during social dominance tests one day affected the mice's performance - without any stimulation - the next day; mice receiving more than six photostimulated wins all maintained their new rank, whereas most mice receiving fewer than five photostimulated wins returned to their original rank, the authors report.

 http://science.sciencemag.org/content/357/6347/162