The nucleus accumbens core (AcbC), anterior cingulate cortex (ACC), and central nucleus of the amygdala (CeA) are required for normal acquisition of tasks based on stimulus-reward associations. However, it is not known whether they are involved purely in the learning process or are required for behavioral expression of a learned response. Rats were trained preoperatively on a Pavlovian autoshaping task in which pairing a visual conditioned stimulus (CSϩ) with food causes subjects to approach the CSϩ while not approaching an unpaired stimulus (CSϪ). Subjects then received lesions of the AcbC, ACC, or CeA before being retested. AcbC lesions severely impaired performance; lesioned subjects approached the CSϩ significantly less often than controls, failing to discriminate between the CSϩ and CSϪ. ACC lesions also impaired performance but did not abolish discrimination entirely. CeA lesions had no effect on performance. Thus, the CeA is required for learning, but not expression, of a conditioned approach response, implying that it makes a specific contribution to the learning of stimulus-reward associations.Environmental stimuli that are associated with rewarding events thereby gain motivational significance through Pavlovian conditioning processes. Appetitive conditioned stimuli (CSs) have many properties, among which is the ability to attract attention and elicit approach (Hearst & Jenkins, 1974;Tomie, Brooks, & Zito, 1989). This conditioned approach response often has the beneficial function of drawing animals (including humans) closer to sources of natural rewards, such as food, but it may also play a detrimental role in attracting humans toward artificial reinforcers such as drugs of abuse, maintaining addiction and inducing relapse (Altman et al., 1996;Tiffany, 1990). For example, individuals with a propensity to form and respond to Pavlovian stimulus-reward associations have been suggested to be more vulnerable to addictive drugs (Tomie, 1996). It is therefore important to understand the neural mechanisms by which animals learn associations between stimuli and rewards, and the manner in which such associations control behavior.Autoshaping (Brown & Jenkins, 1968) is a measure of Pavlovian stimulus-reward learning in which subjects approach a CS that predicts reward. In a typical autoshaping task designed for use with rats , a visual stimulus (CSϩ) is presented on a computer screen and followed by delivery of food at a different location. A second stimulus (CSϪ) is also presented but never followed by food. Though the subject's behavior has no effect on food delivery, normal rats develop a conditioned response in which they selectively approach the food-predictive CS before returning to the food hopper to retrieve the primary reward. The autoshaped conditioned approach response is generally held to be under the control of Pavlovian, not instrumental, contingencies (Browne, 1976;Jenkins & Moore, 1973;Mackintosh, 1974;Williams & Williams, 1969), and this has been confirmed for the rat autoshaping task described .A...
