Every sports coach who has sought to inspire players with the message that victory is a mental state can rejoice. The claim has been vindicated with the discovery that zebrafish battles are won and lost in the brain, along with identification of the regions that determine success and failure.

“Most animal conflicts aim at establishing a social hierarchy rather than causing lethal damage to opponents,” a paper in Science has reported. After all, physical conflicts can do harm even to the winner. Long before Sun Tzu, a chinese military strategist and philosopher, animals knew that “The greatest victory is that which requires no battle.” Nevertheless, as human history reveals, judging when to fight and when to run is hard.

To investigate the neural mechanisms underlying these decisions, a team led by Dr. Hitoshi Okamoto of the RIKEN Brain Science Institute in Japan put pairs of male zebrafish in tanks. The fights began as usual, "starting with each animal exhibiting display behaviors, followed by circling and biting attacks, and ending when one fish shows fleeing behavior indicating surrender,” the authors wrote.

Previous work by the same team led them to believe two areas of the dorsal habenula, known as the dHbL and the dHbM, play an important part in controlling aggression levels in zebrafish during such encounters. Imaging of neural activity revealed very different patterns lighting up the brains of fish that won and lost.

^{The brains of fish that win and lose battles light up in different parts of the dorsal habenula. RIKEN}

The team used genetic engineering to suppress one of the two brain regions in different fish, using genes that are specifically expressed in these areas. “The dHbL-silenced fish showed a significantly higher tendency (15 out of 20) to lose fights,” the paper reported.

The authors checked to see that the “predisposition to losing” wasn't a result of reduced physical fitness. The engineered fish could last just as long in a fight, and get in as many bites as their wild-type siblings. They lacked the will to win, or perhaps the belief they could. This is despite the fact that the dHbL-silenced fish showed just as much aggression on tests – such as trying to bite themselves in a mirror – as non-dHbL-silenced fish.

Silencing the dHbM region had the reverse effect, with these fish winning 19 out of 27 fights.

In contests between non-engineered fish, the one who got in the most bites in the first two minutes usually won, even without physical advantages. As further evidence for the theory that winning is largely mental, a fish that had won a previous battle was more likely to win another against a new rival if it came within an hour of the first fight, suggesting that feeling like a winner gives the fish an advantage. The effect wears off, however, and after 24 hours the previous victory or defeat made no difference.

This “winner effect” was of little value to dHbL-silenced fish, however. Even their rare wins were not enough to shake their losing mentality.

“These same circuits exist in all vertebrates, including humans, with possibly the same bistable mechanism," Okamoto said in a statement.

Maybe the silencing of specific brain regions will be the next drugs-in-sport scandal.