Neuronal dendrites in the central nervous system undergo cycles of growth and shrinkage (refinement) during development to establish functional neuronal networks, but what regulates these essential reorganisations? For a central serotonergic neuron (CSDn) in Drosophila, suggest K. VijayRaghavan and colleagues, the answer to this question is neuronal activity and Wnt signalling (see p. 1351). The dendrites of the CSDn grow extensively in the antennal lobe during early pupal development but then shrink to form the final adult structure. The researchers show that the arrival of sensory neurons at the antennal lobe correlates with the initiation of CSDn dendritic refinement and that sensory input, possibly acting through NMDA-type receptors (glutamate receptors that control synaptic plasticity), is necessary for dendritic refinement. Furthermore, Wnt activity is increased in response to sensory inputs, and increased Wnt signalling stimulates dendritic refinement. Thus, the researchers suggest, neuronal activity and Wnt signalling interact to refine the dendritic pattern of the CSDn to its ultimate functional state.