For example, a red vertical

stimulus is incongruent, requiring a rightward PR-171 price saccade under the color rule and a leftward saccade under the orientation rule. In contrast, a red horizontal stimulus requires a rightward saccade for both rules. The majority (70%) of trials were incongruent, ensuring the animal always followed the rule. After the animal made the correct saccade, a juice reward was delivered via a juice tube. There was an intertrial interval of approximately 100 ms before the next trial began. Although the rule was cued on each trial, the rule in effect was blocked into groups of trials. Each block consisted of a minimum of 20 trials of the same rule. After 20 trials, the rule switched randomly—with Selleckchem Dactolisib a 5% or 10% chance of switching rules on each trial for monkey ISA and CC, respectively. The average block consisted of 39 trials of the same rule for ISA and 30 for CC. A generalized linear model

(GLM) was used to quantify the effect of multiple task-related covariates on the animals’ behavioral reaction time. A gamma distribution was used in the model, as it is ideal for fitting strictly positive data with a constant coefficient of variation, such as reaction times (McCullagh and Nelder, 1989). The link function, which defines a nonlinear transformation between the linear predictors and the mean of the observations, was chosen to be the log function to enforce the requirement that reaction times be strictly positive. A complete model was developed, fitting the reaction time secondly with all task-related covariates: the rule (color/orientation), preparatory period, congruency of stimulus-response association across rules, monkeys, time in session, and whether it was a switch trial (see Supplemental Information for details). A bias-corrected percent explained variance statistic (ωPEV) was used to evaluate neural selectivity.

ωPEV determines the portion of variance of a neuron’s firing rate explained by a particular task variable (e.g., the current rule) but is analytically corrected for upward bias in percent explained variance with limited observations. Significance was determined by a permutation procedure (see Supplemental Information for details). The LFP was transformed into the time-frequency domain using Morlet wavelets. Synchrony was estimated by computing the spectral coherence between pairs of electrodes. Significant differences in coherence between the two rules were determined with a permutation test. The null hypothesis is that no significant difference exists between rules, therefore a null distribution was generated by permuting color and orientation trials and recalculating the coherence (this process was repeated at least 100 times for each pair of electrodes).