Role of the anterior cingulate cortex in the control over behaviour by Pavlovian conditioned stimuli

The anterior cingulate cortex (ACC) has been clearly implicated in stimulus–reward learning, but the exact contribution it makes to this process is not well understood. To address this issue, rats with lesions of periand postgenual ACC were tested using a variety of tasks to which stimulus–reward learning was expected to contribute. Unexpectedly, rats with ACC lesions learned to approach a food alcove during a stimulus that predicted imminent food delivery (temporally discriminated approach task), and subsequently responded normally for that stimulus in a test of conditioned reinforcement. They also exhibited normal conditioned freezing to an aversive CS that predicted footshock. Yet the same animals were impaired at autoshaping, a deficit observed before in ACC-lesioned animals. Furthermore, an autoshaping deficit was demonstrated when subjects received the lesion after training, though some behavioural recovery occurred. Additionally, the phenomenon of simple Pavlovian–instrumental transfer was intact following ACC lesions. In order to resolve the apparent discrepancy between the autoshaping deficit and the lack of a deficit on the temporally discriminated approach task, a new task was developed in which the approach behaviour was identical to that measured during the temporally discriminated approach task, but was under the control of two stimuli, only one of which was followed by reward. ACC-lesioned rats were impaired at the discrimination, approaching during both stimuli. It is suggested that this region of the ACC is not critical for stimulus–reward learning per se, but is required when multiple stimuli must be discriminated on the basis of their association with reward. Analogies with primate ACC are discussed.