Rules for differentiation and axon guidance Differentiation rule, whereby individual ENC agents differentiate into non-proliferative and non-motile enteric neuron agents stochastically, at a set population frequency Axon production rule, whereby neuron agents project an axon that is stable over time and whose course reflects the trajectory of its growth cone. Axon movement and guidance rule, whereby growth cone movement has similar rules to that of ENC agents, except that axons cannot turn directly back along their own axon.