Once a simulation is triggered by the run() directive in System the simulation evolves according to a fixed loop structure.

First System will call all the evolve() methods of all registered instances of SpikingGroup. During this step all dynamic ODEs of the the neuron and synapse models are updated. Then in a second step it calls all propagate() methods of instances of Connection objects. This generally takes care of propagating spikes produced by any SpikingGroup and delivers them to NeuronGroups where they have their effect on the specified transmitter target (see TransmitterType). Now all Monitors are called via their propagate() function. This is mainly to write results to files or do some online monitoring (see Checker). In a final step the evolve() function of Connection objects are called. This is generally to implement continuous weight updates caused for instance by a synaptic decay.