Figure 3
Burst coding despite unimodal inter-spike interval distributions. (A) The ISI distribution of the encoding population is plotted for three example relative refractory periods. Distribution is unimodal for very short \(\tau _{\text{rel}} = 2\) (i) and short \(\tau _{\text{rel}} = 7\) (ii) refractory periods, but bimodal for long \(\tau _{\text{rel}} = 28\) (iii) ones (rate compensated data is shown). (B) A lower bound on mutual information is plotted as a function of Fourier-frequency for both the driver (blue) and modulator (red) channels. Integrating the lower-bounded information over frequency and summing driver and modulator channels produces estimates of linearly encoded information of (i) 131.58 bits/s (ii) 148.91 bits/s, and (iii) 156.64 bits/s for each distribution shown in (A), respectively. (C) Normalized Information rate is shown as a function of relative refractory period for the driver channel (blue, up-arrowhead), the modulator channel (red, down-arrowhead) and both channels together (black, square). The purple bar indicates the region of parameter space producing visually unimodal ISI distributions (those exhibiting only a single peak). For each value of the relative refractory period, the firing threshold for neurons in the encoding population was scaled to preserve the same average firing rate for all values of the relative refractory period. (D) As in (C) but without adjusting cell firing threshold. Normalization in (C,D) is by the maximum (over \(\tau _{\text{rel}}\)) linearly decoded information rate, for perfectly decoded events and bursts.
