Mice watching fights show experience-like brain changes

Researchers reported in Nature that mice that watched aggression and mice that took part in it developed the same behavioural strategy and similar changes in subcortical neural activity. The work used longitudinal, cell-type-specific recordings across the social behaviour network, which includes the hypothalamus, amygdala and midbrain. Animals were trained over 8 days and then tested in a new aggression context. doi.org

Training and testing design

Mice were split into three groups. The experience group (EXP) practised aggression in a safe, easy-to-win setting: three 10-minute sessions per day for 8 days with a novel submissive mouse in the home cage. The observation group (OBS) was placed on a platform above similar fights and received multimodal cues but could not interact with the animals below. The control group (NON) got a mouse toy for sessions of matched duration. doi.org

After training, all groups faced the same probe test: a novel context with a harder opponent, a similarly sized mouse with previous aggression experience, in three 4-minute interactions. Behaviour was quantified with supervised classifiers, fine-grained annotation and unsupervised clustering. doi.org

Shared behaviour and reduced inhibition

Both EXP and OBS mice showed a shared adaptive strategy in the hard fight, including more proactive aggressive and vigilance behaviours. This strategy was absent in animals without training. doi.org

During observation, the watched behaviour activated widespread regions of the network, and subsets of regions preferentially encoded different axes of the observed behaviour. This activity mimicked that evoked by experienced behaviour, and the shared neural changes persisted into the novel context. doi.org

Multiregion modelling showed shared changes in a core aggression network after both experience and observation, including a widespread reduction in inhibition. The networks gradually became more biased toward excitation. doi.org According to the authors, this reduction is necessary for the adaptive behavioural change: reactivating key subcortical inhibitory regions after observation returned observers to a naive, less-proactive state. doi.org

The authors conclude that experience-like activity during aggression observation can engage a shared inhibitory plasticity mechanism that biases behaviour toward proactive strategies. doi.org

Observing aggression in mice changes behaviour and reduces subcortical inhibition like direct experience

Training and testing design

Shared behaviour and reduced inhibition

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