Figure 3.

Information transmission for a natural spike train. A, Relative deviation of approximation for mutual information from exact numerical calculations. The approximation presented holds true with 95% accuracy for all firing rates between 0.01 and 56 Hz and train durations of 100 spikes, as well as for spike trains shorter than ∼40 spikes at all rates tested. For spike trains longer than ∼40 spikes at rates of 64 Hz and above, significant deviations appear. The approximation accuracy is reduced when the model is stressed to the point when the release probability during prolonged high-rate stimulation approaches zero. B, The average cumulative mutual information I_cumulative for a natural spike train. I_cumulative shows rapid changes during natural spike trains with peaks corresponding to spike bursts and decays corresponding to periods of low activity. Information transfer in a dynamic synapse based on measured data starts as low as for a static synapse with a P_r = 0.2, but then increases during bursts, due to STP, to reach the performance of a static synapse with a P_r = 0.4. C, Mutual information per unit time for the first 70 spikes in the train plotted for a dynamic synapse with a basal P_r = 0.2 and static synapse with P_r from 0.2 to 0.4. The dynamic synapse expresses a wide range of transferred information values during the natural spike train from that similar to a static P_r = 0.2 synapse to above that of static P_r = 0.4 synapse.