Neuronal detection of social actions directs collective escape behaviour.

Animals in groups obtain information from social partners to engage in adaptive behaviour 1-3 . Social information transmission is observed in fish schools 4-6 , bird flocks 7,8 and human groups 9,10 , but the neural representation of such socially acquired information is poorly understood 3,11,12 . Here we show that, in the schooling glassfish Danionella cerebrum 13-15 , collective escape from danger can be mediated by an individual's visual perception of other escaping animals. To understand the neural basis of socially transmitted escape behaviour, we imaged neural activity from adult glassfish viewing the actions of virtual conspecifics. Visual neurons in the midbrain optic tectum 16,17 and thalamus 18 increased their activity when virtual conspecifics escaped. Escape-responsive neurons also responded to the sudden disappearance of virtual fish, yet were unaffected by the disappearance of stimuli moving with non-biological linear motion. Behaviourally, fish retreated from virtual schools that escaped or disappeared, but only those swimming with biological burst-and-glide motion. Neural encoding of this rapid social offset allows fish to infer danger from social information alone, a potentially effective strategy for animals that are capable of rapid movement but have a limited visual range 14,19 . These results show how the neural computations of individuals enable rapid information sharing in collectives.