1. A method for producing spike-dependent plasticity in an artificial synapse comprising: generating a pre-synaptic spiking event in a first neuron when a total integrated input to said first neuron exceeds a first predetermined threshold; generating a post-synaptic spiking event in a second neuron when a total integrated input to said second neuron exceeds a second predetermined threshold; after said pre-synaptic spiking event, applying a first pulse to a pre-synaptic node of a synapse having a phase change memory element; and after said post-synaptic spiking event, applying a second varying pulse to a post-synaptic node of said synapse, wherein current through said synapse is a function of the state of said second varying pulse at the time of said first pulse.