1. A neural network, comprising: a processor; multiple heterogeneous neuron populations that operate at different time scales, wherein each neuron population comprises: at least one digital neuron; and a time scale generation circuit that controls timing for operation of each neuron of said neuron population by: counting the number of clock steps generated by a clock; and generating a time step upon determining that the number of clock steps reaches a time scale threshold parameter of said neuron population, wherein the time step generated triggers each neuron of said neuron population to integrate neuronal firing events at a time scale corresponding to said neuron population; and a plurality of synapses interconnecting the neurons, wherein each synapse interconnects a neuron with another neuron, and wherein at least one neuron receives neuronal firing events from an interconnected neuron that operates at a different time scale.