Activations in neuroimaging experiments demonstrate a correlation between a component of the experimental task and an indirect measure of neuronal activity, but cannot establish whether or not the region is essential for that function. As well as evidence from neuroimaging, a large number of electrophysiological studies in monkeys have reported cells in the ACCs which respond to errors or reductions in reward which facilitate corrective behaviour (Amiez, Joseph and Procyk, 2005; Ito, Stuphorn, Brown and Schall, 2003; Shima and Tanji, 1998). However, while changes in the way errors are handled after ACC lesions have been reported (Fellows and Farah, 2005; Rushworth, Hadland, Gaffan and Passingham, 2003; Shima and Tanji, 1998; Swick and Turken, 2002), the degree of disruption is inconsistent. One possible reason is that, for a foraging animal like a macaque monkey gathering food in an uncertain environment, courses of action are rarely categorically either correct or incorrect. Instead, rather than simply considering the outcome of the immediately preceding response, the animal will have to use its history of positive and negative reinforcement in order to decide between competing options.
