Fig. 3.

Pattern discrimination. The first 25 synapses 1 ≤ j ≤ 25 are stimulated by Poisson input with a rate ν^pre = 2, 13, 25, and 40 Hz that changes each second. The remaining 75 synapses receive Poisson input at a constant rate of 20 Hz. (A Upper) Evolution of all synaptic weights as a function of time (red; strong synapses, w_j ≈ 1; blue: depressed synapses, w_j ≈ 0). All synapses are initialized at the same value w_j = 0.1. (Lower) The evolution of the average efficacy of the 25 synapses that receive pattern-dependent input (red line) and that of the 75 other synapses (blue). Typical examples of individual traces (synapse 1: black and synapses 30: green) are given by the dashed lines. (B Upper) Evolution of the average mutual information I per bin (blue line and left scale) and of the average Kullback–Leibler distance D per bin as a function of time. Averages are calculated over segments of 1 min. (Lower) Output rate (spike count during 1 sec) as a function of pattern index before (blue bars) and after (red bars) learning.