Continuing down the path of defining a BNF for the definition of a spiking neural network (SNN), layers with different properties could expand the capability of the SNN. For instance, an SNN with only spike time dependent potentiation (STDP) is not likely to have the capabilities of a network with both short and long term synaptic modification rules. Yet it could provide some flexibility to the network as a whole to have both types of synapse modification available simultaneously.