Calcium helps neurons identify synaptic targets during development.

Correct wiring of brain circuitry during development involves the selective formation and retention of synaptic connections between neurons. In this issue of Neuron, Lohmann and Bonhoeffer show that dendritic filopodia can distinguish among prospective presynaptic axonal targets during development. Contact with the appropriate target triggers local calcium signals that stabilize the filopodia and tell them to form mature synapses.