Figure 5.

Oscillations—beginning of learning. Here we plotted the same variables as in Figure 3, but the afferents now receive an oscillatory drive. A, Input spike trains. Because of the oscillatory drive input spikes come in waves. Again, pattern periods are shown in gray. Three insets zoom on adequate periods to illustrate that the spike phases of the afferents involved in the pattern (0 … 199) are the same (except for the noise) for different pattern presentations [the phase grid has a 1 rad (20 ms) step]. This is not true for afferents not involved in the pattern (200 … 1999) (however those afferents have the same phases in the two right insets because their activation levels did not change). It is this repeating “spike wave” that STDP can detect and learn. B, Postsynaptic membrane potential as a function of time. It oscillates, since input spikes come in waves. At this time the postsynaptic neuron is not selective: the threshold is reached at least once at each cycle, whether or not the pattern is present. C, Distribution of synaptic weights at t = 3 s. Weights are still almost uniformly distributed at this stage, since few STDP updates have been made. D, Synaptic weights for afferents 0 … 199 (involved in the pattern) as a function of their corresponding pattern activation levels. Both variables are uncorrelated at this stage.