Distribution of spontaneous firing rates (y axis) as a function of f1/f0 ratio (x axis) for all neurons shown as clusters in Figure 4. Neurons with spontaneous rate of ≤0.1 are shown as 0.1. There are two main groups: those with f1/f0 < 1 have spontaneous rates > 1, and those with f1/f0 > 1 have low spontaneous rate. Clusters as in Figure 4. The smaller clusters detailed in the Figure 5 legend are shown with the same symbols used in Figure 5.