Synaptic Modifications in Response to STDP, Purely Presynaptic, or Purely Postsynaptic Stimulation Protocols

<div><p>(A) The relative change in the fraction of synapses in the UP state in response to deterministic (red line) and stochastic (green and blue lines with symbols) STDP stimulation protocols is shown as a function of Δ<i>t</i>. 0 means no net change in number of synapses in the UP state, positive relative change means a net increase of synapses in the UP state, and a negative relative change means a net increase of synapses in the DOWN state. Stochastic stimulation results are shown for <i>k</i>_CaN = 18 1/s (green line with squares, same value as in deterministic case) and <i>k</i>_CaN = 20 1/s (blue line with circles). The inset shows some example calcium transients (dashed lines) of the stochastic stimulation protocol evoked by a spike pair with Δ<i>t</i> = −100 ms and <i>t</i>_pre = 200 ms. The avergage calcium transient is shown by the full line and is the same as the red curve in <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.0030221#pcbi-0030221-g004" target="_blank">Figure 4</a>. (Δ<i>Ca</i>_pre = 0.17 μM.)</p><p>(B) Relative change in the fraction of synapses in the UP state after purely presynaptic, or purely postsynaptic stimulation protocols, as a function of frequency: the stimulation protocol consists of 60 presynaptic (full lines) or postsynaptic spikes (dashed lines) at a given frequency. Red lines: deterministic stimulation, <i>k</i>_CaN = 18 1/s. Green lines with diamonds or squares: stochastic presynaptic or postsynaptic stimulations, respectively, with <i>k</i>_CaN = 18 1/s. Blue line with triangles or circles: stochastic presynaptic or postsynaptic stimulations, respectively, with <i>k</i>_CaN = 20 1/s. In all panels, the stochastic stimulation results are averaged over <i>N</i> = 300 synapses.</p>