Several studies have examined a role for the prelimbic cortex (PL) and infralimbic cortex (IL) in free operant behavior. The general conclusion has been that PL controls goal-directed actions (instrumental behaviors that are sensitive to reinforcer devaluation) whereas IL controls habits (instrumental behaviors that are not sensitive to reinforcer devaluation). To further examine the involvement of these regions in the expression of instrumental behavior, we first implanted male rats with bilateral guide cannulae into their PL, then trained two responses to produce a sucrose pellet reinforcer, R1 and R2, each in a distinct context. R1 received extensive training and R2 received minimal training. Rats then received lithium chloride injections either paired or unpaired with sucrose pellets in both contexts until paired rats rejected all pellets. Following acquisition, in Experiment 1, rats received either an infusion of saline or baclofen/muscimol into the PL and were tested (in extinction) on both R1 and R2. In vehicle controls, both responses were goal-directed actions, as indicated by their sensitivity to reinforcer devaluation. PL inactivation decreased expression of the minimally-trained action without affecting expression of the extensively-trained action. Experiment 2 utilized the same experimental design but with IL inactivation at test. The extensively-trained response was again a goal-directed action. However, now expression of the extensively-trained goal-directed action was suppressed by IL inactivation. The overall pattern of results suggests that the PL is involved in expression of minimally trained goal-directed behavior while the IL is involved in expression of extensively trained goal-directed behavior. This implies that the PL does not control all types of actions and the IL can control some types of actions. These results expand upon the traditional view that the PL controls action while the IL controls habit.
Keywords: Extended training; Goal-directed action; Instrumental; Medial prefrontal cortex; Operant.
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