1. A circuit to model spike timing dependent plasticity of a postsynaptic neuron, the circuit comprising: a calcium integration circuit configured to generate a calcium integration circuit output signal (Catotal) representative of a total concentration of calcium in a postsynaptic dendrite, wherein the calcium integration circuit is responsive to first and second input signals (V glu , V dent ), wherein the first input signal (V glu ) is representative of a glutamate concentration in the postsynaptic dendrite and wherein the second input signal is representative of a postsynaptic dendrite back potential, wherein a magnitude of the calcium integration circuit output signal (Ca total ) is influenced by a relative timing relationship between the first and second input signals, wherein the relative timing relationship is in accordance with the spike timing; and an EPSC transduction circuit coupled to receive the calcium integration circuit output signal (Catotal) and configured to generate an EPSC transduction circuit output signal (EPSC) representative of a change of synaptic strength of the postsynaptic neuron.