The role of the orbitofrontal cortex in sensory-specific encoding of associations in pavlovian and instrumental conditioning.

A wide variety of associative learning tasks have been employed to assess the functional role of the orbitofrontal cortex (OFC) and related structures in learning. Many of these tasks were designed to assess the learning of highly specific associations between Pavlovian conditioned stimuli (or instrumental responses) and the sensory properties of reinforcement (i.e., sensory-specific associations). Current research suggests that OFC lesions impair behavioral control by these sensory-specific associations in unconditioned stimulus (US) devaluation, differential outcome, and Pavlovian-to-instrumental transfer experiments. In addition, although the OFC has been shown to be important in conditioned reinforcement but not in potentiated feeding tasks, versions of these tasks that assess control by sensory-specific associations have either not been run or they have not examined the effects of OFC lesions. Thus, firm conclusions from conditioned reinforcement and potentiated feeding studies cannot yet be drawn. Furthermore, studies examining the OFC's involvement in reversal learning have also suggested that associations between stimuli and reinforcement importantly depend upon a functioning OFC, possibly because this structure is needed to generate outcome expectancies useful in the computation of prediction errors ultimately used to "update" associations elsewhere (e.g., basolateral amygdala). Other work has shown that both original and reversed sensory-specific associations can control performance after different time delays following reversal learning. This suggests that structures outside of the OFC may be involved in the storage of originally acquired associations. Overall, this review makes clear that the OFC plays an important role in the encoding of sensory-specific associations in a wide variety of learning tasks.