The strength

of the contribution of image value (R2val) was quantified as (SSval/SStotal). For each trial after reversal, we then averaged the contribution of image value (R2val) obtained for each cell over all cells in a subgroup. We normalized the population average by dividing by the maximum average R2val. We then fitted the neural data from each subgroup with a Weibull function (Equation 1). Results were similar and statistically significant for both monkeys, so the data were combined. In several instances, check details we fit neural data with a sigmoid curve using a Weibull function: equation(1) f(x)=u+(l−u)exp(−xα)β,which modeled the data as a function of trial number after reversal (Figure 5) or time during the trial (Figures 8E and 8F). The u and l parameters

adjust the upper and lower asymptotes of the fit curve, respectively, and the β parameter adjusts the shape of the curve. The α parameter can be considered to be a scale-adjusted rise latency: it is equivalent to the value of x (trial number) for which f(x) reaches a certain percentage of its maximum value. This value depends upon the upper and lower limits of the fit. Specifically, when x is equal to α, the function reaches a level defined by: equation(2) f(x)≈0.63∗u+0.37∗l.f(x)≈0.63∗u+0.37∗l. We could determine whether the α parameter was significantly different for two data sets by fitting the data twice: once with all parameters free, and once with the α parameter

constrained to be the same for the two data sets. An F-test was used to determine whether separate Idelalisib α parameters explained the data better than a single α parameter—i.e., whether one fit reaches its scale-adjusted threshold significantly earlier than the other. We also examined whether the 95% confidence bounds for the out α parameters overlap. In some cases, we report the difference between the α parameters to quantify the separation between two curves. To evaluate the detailed time course of changes in neural activity and behavior after reversal, we performed a sliding ANOVA analysis. For every value-coding cell, we divided each trial into 200 ms bins that were slid across the trial in 20 ms steps, and obtained the spike count for each bin. Then, for the data from each bin, we calculated the two-way ANOVA using the last six trials of each type before reversal, and a group of six trials of each type after reversal, slid in one-trial steps. Again, the total variance obtained from each iteration of the ANOVA (SStotal) was partitioned into image value (SSval), image identity (SSid), interaction (SSint) and error (SSerr) terms. The strength of the contribution of image value (R2val) was quantified as (SSval/SS). The proportion of total explainable variance (SSexp) was calculated as (1 − SSerr/SStotal).