Strong competition rewires the brain in ways that echo the words of Abba hit The Winner Takes It All, a study has found.
In mouse "turf wars", repeated defeats reduced activity in the frontal cortex of the brain.
Boosted activity in the same region was seen in mice that continually emerged the winner in territorial disputes. The frontal cortex is the "higher" area of the brain controlling decision making and planning.
A connection breakdown between this region and the "lower" brainstem which co-ordinates motor and sensory signals also occurred in defeated mice. As a result, they were likely to be less defensive and more fearful and anxious.
The findings may explain why repeated knocks can lead both mice and humans to become passive and depressed.
Victorious mice - and perhaps humans too - tend to get increasingly aggressive and dominant. The neural effects of winning and losing seem to be reflected in the lyrics of the Abba song, which include the line: "The winner takes it all; the loser's standing small."
Senior researcher Dr Tamara Franklin, from the European Molecular Biology Laboratory (EMBL) in Monterotondo, Italy, said: "Our findings explain how repeated winning and losing reprograms the brain to prepare for future encounters. By studying brain changes induced by repeated victory or defeat, we can learn about the brain circuits that control depression-like behaviour."
The study involved territorial engagements between male laboratory mice. Scientists measured electrical activity of the animal's brains and looked at a molecular marker of neural rewiring. Long-term changes in the brain's functional connectivity were seen to result from winning or losing social encounters.
The scientists presented their findings at the Neuroscience 2012 meeting in New Orleans, US.
In a summary of their research they wrote: "This suggests that the baseline connectivity of particular brain areas is altered by repeated aggressive encounters, providing a possible factor underlying the likelihood that an animal takes a passive rather than an active role during social confrontations. Findings provided here further highlight plasticity in the adult brain as a result of social interactions, and have implications for the functional neuroanatomy underlying depression."