 Every day, we find ourselves at a virtual crossroads when it comes to making decisions. Should I get out of bed now? What should I wear? What should I eat for dinner? Interestingly, the choices we make, and thus who we are, depend on what goes on at the very real crossroads where the billions of neurons in our brain intersect. Like tiny traffic lights, these regions between neurons, or synapses, direct the flow of information. Excitatory synapses signal go, whereas inhibitory synapses signal don't go. While scientists have a good grasp on how mature synapses exert their traffic signaling function, it's less clear how and where synapses are formed in the first place. To understand the rules guiding early synapse formation, scientists at the Max Planck Florida Institute for Neuroscience developed a cutting-edge technique that allowed them to precisely control where synapses formed and watch how they developed in real time. Decades of research has shown that activity generated by developing circuits plays an important role in how and where synapses are formed. However, many studies have focused on the role of the signaling molecule glutamate in excitatory synapse formation, because glutamate conveys the go signals. Less attention has been paid to the role of the molecules that convey the don't-go signals, because they usually act to stop activity. GABA conveys these signals at typical inhibitory synapses. To figure out how GABA affects synapse development, the scientists first had to figure out how to control GABA signaling at the spatial scale of individual synapses. They bathed live brain tissue from mice with chemically caged GABA molecules. Caging the molecules suppressed their ability to signal the way they normally do, but by zapping them with laser light, the scientists could set molecules in specific locations free and thus precisely control where GABA could affect synapse formation. By monitoring GABA's effects with the same level of precision, the scientists observed that GABA, despite its typical association with only inhibitory synapses, could stimulate the formation of excitatory as well as inhibitory synapses. Similar experiments revealed that glutamate could only stimulate excitatory synapse formation, making GABA the principal architect of the brain's synaptic layout. These results reveal a new role for GABA during development. By shaping where excitatory and inhibitory synapses form in the brain, GABA can sculpt the neural circuits that determine how the brain works, ultimately making us who we are.