Filling a notable gap in scientists' understanding of how cells respond to "smells" and signal to underlying neurons, researchers report that the activated cell receptors cause their cells not simply to fire, but to fire in specific patterns. Then, cells with the same firing patterns end up connected at the same nerve clusters, or glomeruli, in the brain's olfactory bulb. With this strategy, the authors say, neurons with overlapping features can generate variation in their ability to respond to sensory cues related to smell. Previous work has shown that olfactory receptors (ORs) participate in wiring the mouse olfactory system through their signaling activity and its effects on neurons, including the olfactory receptor neuron (ORN). Whether this activity actually informs the wiring of the brain's olfactory system has been unclear, however. Here, to investigate the potential instructive role of neural activity in this process, Ai Nakashima and colleagues used a series of in vitro experiments and mouse studies where they changed neural activity patterns through optogenetics and studied the effects on the expression of molecules important in the olfactory system. They report that different patterns of activity in olfactory sensory neurons altered expression of molecules in nerve endings - targeting them to specific nerve clusters in the olfactory bulb. Neural activity appears to drive expression of key proteins in the olfactory system not simply by driving neural firing, they say; rather, specific features of neural activity are important to the patterns of gene expression in this process.