Stochastic properties of synaptic transmission affect the shape of spike time-dependent plasticity curves

Theoretical studies have shown that calcium influx through N-methyl-D-aspartate ( NMDA) receptors is a sufficient signal to account for various induction protocols of bidirectional synaptic plasticity, including spike time - dependent plasticity (STDP). The STDP curves obtained by these different models exhibits a form of spike time - dependent long-term depression that occurs when a presynaptic spike precedes the postsynaptic spike (pre-post LTD). We have previously proposed that this novel form of LTD can serve as an experimental test for the validity of these models. These calcium based theoretical models assumed deterministic calcium dynamics that reflect average properties of synaptic calcium currents. In this paper, we show that taking into account the stochastic properties of synaptic transmission significantly alters the form of STDP curves and may significantly reduce the magnitude of pre-post LTD.