Fig. 7.

Dependence of calcium transients of nonlinear plasticity model on the stimulation protocol and on the extracellular calcium concentration. Example model calcium transients resulting from a single pre-post pairing at Δt = 10 ms (A) and Δt = −25 ms (B), a presynaptic spike paired with a burst of three postsynaptic spikes (C), and a pre-post pair repeated at a frequency of 10 Hz (D). Transients for all stimulation protocols are shown for the three extracellular calcium concentrations used in the experiment (rows). The linear pre- and postsynaptic contributions are shown in cyan and magenta, respectively, together with the spike times indicated by the vertical lines. The nonlinear contribution is shown in purple. The transients depend strongly on the relative timing of pre- and postsynaptic activity, primarily due to the model’s nonlinearity. The long decay timescale of the nonlinear term implies that calcium returns to baseline slowly and thus may accumulate for induction protocols with high pairing frequencies.