Escape neurons in glassfish fire when a virtual neighbour vanishes from the screen

Geoff Meyerhof, a postdoctoral fellow in the lab, made the social cue available without a predator. He designed schools of virtual Danionella in video game software, realistic enough in appearance, posture and movement that real fish came and swam alongside them at the screen ^[5]. When the on-screen school suddenly fled, the real fish scattered as though a threat were present, with nothing approaching the tank ^[6]. Seeing a partner escape is sufficient on its own ^[16].

That design has an obvious failure mode. A fish might be startled by any object that shoots off or drops out of view, social or not. The smooth-motion condition addresses it: the same virtual school, gliding along with non-biological smooth motion, neither recruited real fish nor alarmed them ^[8]. The authors concluded that the glassfish brain identifies social partners by the natural movement pattern of its own species, and is highly sensitive to their sudden disappearance from an expected position ^[9].

The recordings covered thousands of neurons across the brain, read through a transparent body about 12 millimetres long with an optical microscope ^[3][4]. What they give is a correlation. Neurons that respond when a partner flees have not been shown to cause the flight, and the account describes recordings without perturbations ^[18]. The release does not include group sizes or escape rates ^[17].

The same lab had already shown that glassfish school by watching and copying their neighbours' actions ^[15]. "Each fish in the group sees their neighbors move, and moves in response," said Matthew Lovett-Barron, the assistant professor of neurobiology whose lab ran the work, describing the interaction that produces schooling ^[13]. "The ability to pay attention to each other helps these fish detect danger as well," he added ^[14]. In the real schools, fish on the far side from the looming object escaped when they could see nearer neighbours fleeing it ^[12].

The sensitivity to a partner's absence fits where this animal lives. Danionella cerebrum is found in murky water and may not be able to see very far there, which the authors compare to human vision in dense fog, where fast-moving items can seem to vanish from view ^[10]. Jo-Hsien Yu, who led the study as a doctoral student in the lab, reported the result in Nature ^[2][1].