Abbott, LF. Varela, JA. Sen, K. Nelson, SB. (1997) Synaptic Depression and Cortical Gain Control. Science 275: 220-224.
Model of STD is implemented by decreasing excitatory amplitude by factor f, whenever there's a presynaptic spike. Amplitude recovers exponentially back to 1. This changes the total amount of current that enters the cell as a function of rate. This makes the neuron sensitive to relative changes in the rates of the presynaptic neurons. With depression a 50% change in a 100Hz input, and a 50% change in a 10Hz input has about the same effect on the output.