Figure 2. Risk-sensitive orbitofrontal neurons fail to conform to specific predictions for representation of risk.

a, b, Time course of average peak-normalized firing rates in risk-responsive neurons ((33% and 67%) > (100% and 0%) or the opposite, respectively, P < 0.05, Mann-Whitney U-test) on trials associated with different probabilities of reward (blue, 100%; orange, 67%; red, 33%; cyan, 0%) aligned to responding at the fluid well. Shading, s.e.m.. c, d, Average firing during the outcome anticipation period (1 s) as a function of reward probability for 53 neurons shown in a and 67 neurons shown in b, respectively. Error bars, s.e.m. e, f, Distribution of activity indices contrasting average firing in anticipation of 100% versus 0% reward during the outcome anticipation period. Activity indices were calculated as follows: (firing rate in anticipation of 100% reward (“100”) – firing rate in anticipation of 0% reward (“0”))/(“100”+ “0”) for e or (“0” − “100”)/(“0” + “100”) for f (blue bar, neurons which fired significantly more in anticipation of 100% than 0% reward; cyan bar, neurons which showed the opposite pattern, P < 0.05, Mann-Whitney U-test). The distributions were shifted significantly above zero (P < 0.001, Wilcoxon signed-rank test). g, h, Distribution of activity indices contrasting average firing in anticipation of 33% versus 67% reward during the outcome anticipation period. Activity indices were calculated as follows: (firing rate in anticipation of 33% reward (“33”) – firing rate in anticipation of 67% reward (“67”))/(“33”+ “67”) for g or (“67” − “33”)/(“67” + “33”) for h (red bar, neurons which fired significantly more in anticipation of 33% than 67% reward; orange bar, neurons which showed the opposite pattern, P < 0.05, Mann-Whitney U-test). The distributions were shifted above zero (P value is from Wilcoxon signed-rank test).