Methods, systems, and apparatus, including computer programs encoded on a computer storage medium for generating model neurons. In one aspect, a method includes receiving a plurality of descriptions of branches of dendrites of one or more neurons and generating a collection of model neurites. Each of the descriptions characterizes, for an individual branch, i) a distance from a cell body at which the individual branch first bifurcates and ii) a distance from the cell body at which the individual branch actually terminates. Generating the collection of model neurites includes repeatedly selecting a description of a branch from the plurality and probabilistically generating a topology of a model neurite based on the selected description. The probabilistic generation of the model neurite includes deciding whether to bifurcate, terminate, or continue the model neurites at different positions based on the selected description.