Brains are used to make behavioral choices about what to do next. Animals with two sides, including humans, constantly make choices about whether to respond to the left or right. Do they look left, or look right; turn left or right; reach left or right? Surprisingly, we know little about the wiring of the nerve cells in the brain that accomplish the task of making such left/right choices – one of the simplest, but most important behavioral choices made by two-sided animals like us. This paper uses an interdisciplinary neurotech collaboration to reveal such a circuit in the brain of zebrafish.