The failure of animals with ACC lesions to identify the response with the better reward yield (Kennerley et al., 2006) could be BTK inhibitor interpreted as the consequence of an impairment in a mechanism for encoding the reward rate associated with a response or an impairment in the use of such information to decide whether or not to try switching to making an alternative response. A related

idea, discussed in more detail below, is the possibility that ACC encodes certain types of costs, as well as the benefits, that are associated with a choice. The exact nature of the response that will be made at the end of the decision does appear to be important for ACC neurons. Kennerley et al. (2009) trained each of their two macaques to respond in different modalities with either eye movements or arm movements. Response selectivity was more apparent in ACC in the second case. The difference in selectivity might Cytoskeletal Signaling inhibitor reflect the precise placement of the recording electrodes with respect to regions of cortex specialized for representing one type of response or the other

(Wang et al., 2004 and Amiez and Petrides, 2009). Alternatively, however, it may reflect the fact that the nature of the response itself may impact on the value of a course of action; if a course of action is difficult to execute or effortful then the costs of pursuing that course of action may need to be weighed against the potential benefits before a choice is made. A second and related dimension of difference between ACC and OFC concerns the way in which the areas encode the costs, in addition to the benefits, of a choice. Rangel and Hare (2010) argue that there is an important difference between costs that are tied to the outcome itself and

costs that are tied to the action that is used to obtain the outcome. The first type of cost might include an aversive outcome that occurs at the same time as an appetitive outcome or the delay that elapses before the reward arrives. The second type of cost might include the effort almost that has to be expended in order to perform the action that is needed to obtain a reward. lOFC and vmPFC/mOFC are more concerned with the first type of cost and the ACC is more concerned with the second type of cost. In the rat OFC lesions lead to impulsive decision-making and an impaired ability to wait for a longer time in order to receive a larger reward (Rudebeck et al., 2006). By contrast ACC lesions lead to apathetic patterns of decision-making such that a rat is no longer prepared to invest effort in taking a course of action in order to obtain a larger reward (Walton et al., 2002, Walton et al., 2003 and Rudebeck et al., 2006). The effort versus delay cost distinction has also proved useful for understanding differences between primate vmPFC/mOFC and ACC. Prévost et al.