Lesions of Medial Prefrontal Cortex Disrupt the Acquisition But Not the Expression of Goal-Directed Learning

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Abstract
Several studies have established that pretraining lesions of the medial prefrontal cortex (mPFC) render instrumental actions insensitive to devaluation of the instrumental outcome and degradation of the action-outcome contingency. Nevertheless, it remains to be assessed whether the involvement of the mPFC in goal-directed action is limited to the acquisition or to the expression of the action-outcome association in performance. The current series of experiments investigated this issue by comparing the effects of mPFC lesions made either before or after initial training using sensitivity to outcome devaluation as an assay of goal-directed performance. Whereas pretraining lesions left performance insensitive to outcome devaluation, posttraining lesions spared this effect. To determine whether the effect of mPFC lesions on outcome devaluation was the result of a more fundamental deficit in response selection, experiment 2 assessed the impact of pretraining and posttraining lesions on the ability of the instrumental outcome to selectively reinstate the performance of its associated action after a period of extinction. Although both lesions attenuated the magnitude of instrumental reinstatement generally, they left intact the ability of the instrumental outcome to influence response selection. Experiment 3 investigated the relationship between the outcome-selective devaluation and reinstatement effects and found evidence that these effects are both behaviorally and neurally dissociable at the level of the mPFC. These results indicate that the mPFC is selectively involved in the acquisition, but not the permanent storage or expression, of action-outcome associations in instrumental conditioning.

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