Figure 6.

Histograms of percentiles of prediction accuracies in the distributions of chance level over the entire neuron populations. For each neuron in the population we calculated its prediction accuracy, and then by repeatedly and randomly shuffling its left/right or large-/small-reward labels also its chance-level distribution. We then computed in which percentile of its chance-level distribution the neuron's prediction accuracy lay. A histogram of these percentiles over all neurons is plotted here. Neurons at the top/bottom 5-percentile are designated bias/anti-bias neurons, respectively. (A) The mean percentile of all neurons involved in DLPFC spatial-bias analysis (n = 105) is 66% (green dotted line), and is significantly greater than chance-distribution mean (at 50%, black dotted line; Wilcoxon test p = 2 · 10⁻⁷). Also, 69 of the 105 DLPFC neurons are in the top 50-percentile of the chance-distribution mean, which is significantly more than expected by chance (binomial test p = 8 · 10⁻⁴). (B) The mean percentile of all neurons involved in DLPFC reward-bias analysis (n = 118) is 57% and significantly greater than the chance-distribution mean (Wilcoxon test p = 0.01); 70 of 118 neurons are in the top 50-percentile, significantly more than expected by chance (binomial test p = 0.026). (C) The mean percentile of all neurons involved in VS spatial-bias analysis (n = 52) is 63% and significantly greater than chance-distribution mean (Wilcoxon test p = 0.004); 33 of 52 neurons are in the top 50-percentile, significantly more than would be expected by chance (binomial test p = 0.035).