Prelimbic prefrontal cortical encoding of reward predictive cues.

Animals appoint incentive value and learn to approach otherwise behaviorally inert stimuli if these stimuli come to predict the delivery of reward. Interestingly, this adaptive Pavlovian learning process has been implicated in behavioral control disorders, such as drug addiction. One brain region implicated in directing conditioned approach behavior is the prelimbic region of the prefrontal cortex. The present study employed in vivo electrophysiology in the prelimbic cortex to characterize the distribution of neural responses to the presence of a cue that had acquired incentive value after being associated with a primary reward. Male rats were trained in a Pavlovian autoshaping task in which a lever was presented prior to reward delivery. Following repeated pairings of lever availability and reward delivery, rats pressed the lever even though reward delivery was not contingent on any interaction with the lever. Neurons in the prelimbic cortex selectively encoded the presentation of the reward-predicting lever. Although the response was heterogeneous, most responsive neurons decreased their firing rate in response to the presence of the lever. These findings characterize the varied responses of prelimbic cortical neurons to reward cues and are consistent with evidence that the role of the prelimbic cortex in reward learning depends on the downstream target.