To investigate the role of ACCs in error- and reward-guided action selection, Kennerley and colleagues (Kennerley, Walton, Behrens, Buckley and Rushworth, 2006) taught monkeys a response reversal task where they could make one of two joystick movements (lift or turn) in order to receive food reinforcement (Figure 6a), and examined the effects of discrete lesions to ACCs on performance of this task. On any given trial, only one of the responses was ever rewarded at any one time. The action-outcome relationship remained fixed until the animal had gathered twenty five rewards, after which the contingency reversed and the other movement was now rewarded. Therefore, in order to obtain food at an optimal rate, the monkey had to sustain one response for a number of trials, monitoring the outcome of each action in order to be able rapidly to switch to the other response when the previous one no longer yielded reward. If the ACC is particularly important for error detection and/or correction, then it would be anticipated that lesions to this region would render monkeys poor at updating their actions
