BRAIN MECHANISMS FOR CHANGES IN PROCESSING OF CONDITIONED-STIMULI IN PAVLOVIAN CONDITIONING - IMPLICATIONS FOR BEHAVIOR-THEORY

This article is a review of the results of a series of experiments des igned to identify brain systems involved in appetitive conditioning of rats. It discusses some of their implications for behavioral theories of learning, especially those that concern changes in processing of c onditioned stimuli (CSs). Evidence is presented which suggests that se parable brain circuits are involved in (1) the production of CS-depend ent conditioned orienting responses, (2) the enhancement of CS associa bility produced when expectancies about upcoming events are violated, (3) the reduction of CS associability produced when stimuli are consis tent predictors of other events or are presented without consequence, and (4) the abilities of CSs to serve as reinforcers for second-order conditioning and to be sensitive to postconditioning changes in the va lue of the unconditioned stimulus (US). Finally, none of these circuit s seems critical for normal acquisition of the most common indicator o f Pavlovian conditioning, US-dependent conditioned responses (CRs). Al though the independence of brain pathways does not demand independence of behavioral function, clustering of behavioral phenomena on anatomi cal grounds may provide useful guides for constructing behavior theori es.