Schematic representation of the <i>adaptive</i> STDP phase locking.

<p>Timing between the postsynaptic and the presynaptic spikes is modeled by the spiking phase, . The difference between and , where is some reference value that might be induced by another regulatory inputs, activates the feedback mechanism, “STDP”; the latter activates molecular cascades changing the state, denoted by , of the presynapse and/or postsynapse. Direct STDP feedback is modulated by fluctuations of extracellular medium, (e.g. the metaplasticity), giving rise to the adaptation, i.e. fine tuning of the phase-locked state. A: Presynaptic STDP feedback. B: Postsynaptic STDP feedback. C: STDP curves used in simulations. Positive half-period of the -function indicates potentiation by the increase of presynaptic frequency and/or depression by the decrease of postsynaptic frequency.