Figure 6.

Population activity of burst cells, aligned to EMG onset. A, Population-averaged histogram (±SE) of 116 burst cells. Reaction-block curve includes data from playback- and random-reaction trials. The distribution of dot-turn times in the reaction block is shown in the small green curve preceding EMG onset. The gray region highlights a 300 ms wide time window, which starts 350 ms before EMG onset. For each cell, we calculated the index: (R₁ − R₂)/(R₁ + R₂) in this window. R₁ denotes the mean rate of active and active-delay trials combined. R₂ denotes the mean rate of reaction trials (including random reactions). The inset shows the distribution of modulation indices. Light-gray bins indicate cells with individually significant spike-rate differences between the blocks (unpaired t test; p < 0.01). B, Distribution of modulation indices comparing active and active-delay trials with reaction trials. For each cell, we calculated the same index as in A, at various 300 ms wide time windows, as indicated. C, Mean modulation index over time. The mean modulation index of each histogram in B is plotted. The asterisk indicates a mean value significantly different from zero.