Abstract

The infralimbic medial prefrontal cortex (IL-PFC) has been posited as a common node in distinct neural circuits that mediate the extinction of appetitive and aversive conditioning. However, appetitive extinction is typically assessed using instrumental conditioning procedures, whereas the extinction of aversive conditioning is studied using Pavlovian fear-conditioning. The role of the IL-PFC in the extinction of appetitive conditioning acquired through Pavlovian learning remains largely unexplored. The present studies utilized animal models of Pavlovian- and instrumental-conditioning with sucrose to study the involvement of the IL-PFC in appetitive extinction. Based on fear-extinction we predicted that inactivating the IL-PFC before extinction would have minimal effect on within-session extinction, but would impair the storage of extinction memory. Control studies were conducted in the prelimbic prefrontal cortex (PL-PFC), which is not involved in extinction. PL-PFC inactivation did not affect the acquisition or recall of extinction memory. Counter to our predictions, inactivating the IL-PFC facilitated the extinction of conditioned Pavlovian- and instrumental sucrose-seeking, with no effect on extinction recall tested 24 hr later. In separate studies, inactivating the IL-PFC during a Pavlovian conditioning session in which cue presentations were paired with sucrose did not affect cue-elicited behaviour, but increased responding during inter-trial intervals. The same manipulation performed during instrumental conditioning did not impact lever pressing for sucrose. These findings contradict a growing body of literature suggesting that the IL-PFC is important for the acquisition and consolidation of extinction memory in appetitive conditioning tasks.