Figure 1.

Schematic description of the model of mSTDP. A, Mechanism of LTP with a fast potentiation action and slower downregulation of the instantaneous amount of potentiation at the postsynaptic spike times. The plasticity rule used for LTP is inspired by putative molecular pathways depicted on the left. A pairing protocol between presynaptic and postsynaptic spike trains is illustrated on the right with the time evolution of each variable of the model. The slowly increasing threshold (δw_LTP^th, blue curve) progressively reduces the effect of fast potentiation (δw_LTP, pink curve) on the synaptic weight (w_LTP, thick red lines) at subsequent postsynaptic spike times. The pairing time difference δt is relative to the presynaptic spike time (δt = t_post − t_pre). B, Mechanism of LTD with a fast depression action and a facilitation produced by LTP downregulation at the presynaptic spike times. The plasticity rule used for LTD is inspired by putative molecular pathways depicted on the left. On the right, a triplet protocol illustrates how the progressive lowering of the LTD threshold (δw_LTD^th, blue curve) produced by repeated pre–post pairings can increase the functional impact of fast depression (δw_LTD, pink curve) produced by previous post–pre pairings, resulting in larger depression of the synaptic weight (w_LTD, thick blue lines) at the presynaptic spike times.