Figure 6. Neurons usually fire only their first action potential in the initial 80 ms.

(A) Experimental setup as in Figure 3A. (B) Raster plot (APs, black dots) for an example unit for preferred (left) versus the non-preferred stimulus (right). Red circles indicate the first AP in each trial after the onset of the cortical response. (C) The distribution of times of the first AP for individual discriminating units (grey circles, time bins of 20 ms) for those trials in which the first AP occurred within the initial 300 ms following the onset of the cortical response, for (left) the preferred and (right) the non-preferred stimulus. Black line is the mean across units. Red circle and line through are the median and SEM, respectively. (D) Mean of times of the first AP across trials for individual discriminating units (circles; same trials and window as in C) plotted for the preferred stimulus versus the non-preferred stimulus. Top. Distribution of the mean times for the preferred stimulus. Right. Distribution of the mean times for the non-preferred stimulus. Red circle and line through are the median and SEM, respectively. Right panel. Distribution of the difference in the mean time of the first AP for the preferred and the non-preferred stimulus for all discriminating units. Red circle and line through are the median and SEM, respectively. (E) The distribution of the number of APs across trials for the preferred stimulus for the initial 80 ms after cortical onset for (left) the example unit in (B) and for (right) all discriminating units approximates a Poisson distribution predicted from the mean number of APs (red line). (F) Left panel. The distribution of the number of action potentials (mean across trials) across discriminating units is shown for the preferred stimulus over the initial 80 ms (black) and 300 ms (grey). Last bin also includes units that fired more than 5 APs. Circle and line through are the median and SEM, respectively. Right panel. The number of APs (mean across trials) for individual discriminating units (circles) for the preferred versus the non-preferred stimulus over the initial 80 ms (black) and the initial 300 ms (grey). (G) Area under ROC for individual units (individual lines), based only on the first AP after cortical onset on each trial plotted against the interval from the onset of the cortical response. Statistical significance was assessed same as in Figure 3E. (H) Fraction of discriminating units discriminating depends on the interval from cortical onset. A unit is defined as discriminating if by 300 ms p<0.013.

Figure 6—figure supplement 1. Comparison of neural and behavior discrimination.

(A) Experimental setup as in Figure 3A. (B) Area under ROC curve as a function of time from cortical onset for a 'pooling neuron', which for each trial has all the spikes of N units that are randomly drawn from a pool of all discriminating units (see Methods). Each line is the average of the areas under ROC for 10 different pools of discriminating units. Errorbars are sem. For each area under ROC curve, at each interval, statistical significance for the separation in the distribution of number of action potentials for the target versus the distractor was assessed using Wilcoxon ranksum test (p<0.05). f is at each time interval the fraction of 'pooling neurons' with p<0.05. Blue line is the average probability of a correct choice for all the mice in Figure 4D. (C). Same as B but for all units.