Orbitofrontal Cortex Mediates Outcome Encoding in Pavlovian But Not Instrumental Conditioning

Abstract

Previous studies have implicated the orbitofrontal cortex (OFC) in outcome encoding. However, it remains unknown whether the OFC is selectively involved in pavlovian stimulus-outcome learning or whether it also contributes to instrumental action-outcome learning. In experiment 1, we investigated this issue by assessing the effects of bilateral lesions of the OFC on the sensitivity of instrumental lever press performance to a reduction in the incentive value of the training outcome (a test of action-outcome encoding) and to outcome-specific pavlovian-instrumental transfer (a test of stimulus-outcome encoding). We found that post-training lesions of the OFC did not affect instrumental outcome devaluation, but abolished the transfer effect. Interestingly, lesions made before training had no effect on either task. In experiment 2, we explored the involvement of the OFC in updating stimulus-outcome associations after the underlying contingency, or predictive relationship, between these two events has been degraded. Shams displayed clear contingency learning, withholding conditioned responding to a stimulus that no longer reliably predicted its outcome while continuing to respond to a control stimulus that remained a good predictor of a different outcome. In contrast, OFC-lesioned rats stopped responding to both stimuli, regardless of their predictive status. Together, these findings suggest that the OFC supports outcome encoding in pavlovian, but not instrumental conditioning.