Animals possess specialized networks of neurons in the brain that receive signals about the outside world from the retina and respond by initiating appropriate behavior. Researchers at the Max Planck Institute for Biological Intelligence studied a genetic mutation in zebrafish that eliminates all connections between retina and brain throughout development. The team found that in these ‘deep-blind’ fish the brain circuits are fully functional, as direct brain stimulation with optogenetics can drive normal visual behavior. This shows that the assembly of the brain in zebrafish requires little, if any, visual experience.