From fish schools to human crowds, many species live in social groups where individuals engage with the world and make decisions in cooperation with others. Despite the prevalence of group decision making in the natural world, it is unknown how the brains of multiple individuals share information to coordinate collective actions. In this proposal, I outline a research strategy to study the neural circuits for information sharing and collective decision making in fish schools, by applying modern tools in virtual reality and optical neurotechnology to a unique model system: the transparent micro glassfish. Our approach allows multiple adult glassfish to interact in a shared virtual reality environment, where we can record large-scale neural activity from individuals as we experimentally manipulate their social experiences. This research will provide insights into the function and evolution of cooperation across interacting brains, and the logic of emergent behaviors in social networks.