Mice that only watched fights showed fighter-like behaviour and brain changes in their first fight
In male mice, watching aggression produced a shared behavioural strategy and activity changes in subcortical networks similar to those from direct fighting, the authors report.
A study on nature.com reports that male mice that only watched other males fight entered their own first fight with a strategy resembling that of mice with eight days of direct fighting experience nature.com
nature.comnature.comOpen source ↗. The work comes from the lab of Annegret Falkner at Princeton. The authors recorded activity across subcortical networks for social behaviour while the animals trained. All experiments were done in mice.
Three training groups
Males were split into three groups and trained for eight days, three sessions a day. Fighters had a smaller, submissive mouse placed in their cage for nine minutes per session, so every session was an easy win. Observers sat in a clear-walled compartment of about 4 by 5 by 7 inches (10 by 13 by 17 cm), set on top of another mouse's cage where a fight took place. Cutouts in the barrier let smell and sound through, but the observer could not get down. A control group spent the same time with a toy mouse and saw no fighting.
On day nine every mouse faced three consecutive rounds of four to five minutes in its own cage against an undefeated male with real fighting experience. The groups spent roughly the same amount of time in conflict. What differed was who started it.
Behaviour and neural activity
Fighters and observers both delivered more attacks that drew no response and began sooner than the toy group. They were also attacked less often, while the toy-exposed mice fled more nature.com
nature.comnature.comOpen source ↗. The researchers tracked 15 points on each animal's body in every video frame, and software sorted the footage into 13 recurring behaviours without human labels. Observers and fighters spent more of the fight in close-quarters postures that precede an attack, and less time hanging back. The same lab had linked such proactive postures to resilience in a 2022 study. Jorge Iravedra-García, who led the work, said the transitions between behaviours in observers were also similar to those in fighters.
In the recordings, observing aggression evoked widespread activation across subcortical networks for social behaviour. According to the authors, this activity mimicked the activity evoked by experienced behaviour, and the shared neural changes persisted into the novel aggression context. Observers' brains shifted in the same direction as the fighters' brains, though not as far.
Multiregion modelling showed shared changes in a core aggression network after both experience and observation, including a widespread reduction in inhibition. The authors report that this reduction is necessary for the adaptive change in behaviour.
