The Journal of Neuroscience, May 2, 2007, 27(18):4819-4825; doi:10.1523/JNEUROSCI.5443-06.2007
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Behavioral/Systems/Cognitive
Orbitofrontal Cortex Mediates Outcome Encoding in Pavlovian But Not Instrumental Conditioning
Sean B. Ostlund and
Bernard W. Balleine
Department of Psychology and the Brain Research Institute, University of California, Los Angeles, California 90095-1563
Correspondence should be addressed to Sean Ostlund, Department of Psychology, University of California, Los Angeles, Box 951563, Los Angeles, CA 90095-1563. Email: sostlund{at}ucla.edu
Previous studies have implicated the orbitofrontal cortex (OFC) in outcome encoding. However, it remains unknown whether the OFC is selectively involved in pavlovian stimulusoutcome learning or whether it also contributes to instrumental actionoutcome 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 actionoutcome encoding) and to outcome-specific pavlovian-instrumental transfer (a test of stimulusoutcome 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 stimulusoutcome 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.
Key words: causal learning; contingency; incentive; cognition; motivation; prefrontal cortex; response selection; reward
Received Dec. 15, 2006;
revised March 25, 2007;
accepted March 28, 2007.
Correspondence should be addressed to Sean Ostlund, Department of Psychology, University of California, Los Angeles, Box 951563, Los Angeles, CA 90095-1563. Email: sostlund{at}ucla.edu
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