A method of discovering how neurons are connected to process information is presented here: Design a simple logic circuit that can perform a single, biologically advantageous function. Engineering concepts can be helpful in choosing the function and in designing the logic circuit. Several implementations of the method are reviewed to demonstrate how a biologically advantageous function can be chosen, how one simple network can generate major phenomena that are widely considered unrelated, and how one network design can lead to others that explain entirely different aspects of the brain. These results show that the method can benefit neuromorphic engineering as well as neuroscience, and that some brain functions can be carried out remarkably simply, at least in principle if not in the details.