Comparison of unshifted and shifted STDP.

A. The U-shaped steady-state distribution of synaptic strengths for conventional unshifted STDP. B. The unimodal steady-state distribution of synaptic strengths for shifted STDP (). C. The probability density of pairing intervals for presynaptic and postsynaptic spike trains. The blue area is the symmetric acausal contribution, and the pink area is the additional causal bump arising from postsynaptic spikes induced by the presynaptic input. D. Same as C, but for a stronger synapse. The causal bump is larger and closer to . E. The causal bump superimposed on the unshifted STDP window. The potentiation part of the STDP curve is red and the depression part blue. The causal bump falls entirely within the potentiation domain (red shading). F. Same as E, but for a stronger synapse. The causal bump still falls within the potentiation region. G. Same as E, but for shifted STDP. Part of the causal bump falls into the depression region (blue shading). H. Same as G, but for a stronger synapse. More of the causal bump falls into the depression region.