The Role Of Infralimbic Cortex In Switching Between An Instrumental Behavior’s Status As A Goal-Directed Action Or Habit
In instrumental learning, extensive training of a response typically generates a habit. The transition from goal-directed to habitual behavioral control is often considered unidirectional; however, recent evidence suggests this is not the case. Under certain conditions, goal-directed control may be restored to a behavior that was previously habitual. We identify the infralimbic cortex (IL) as a participant in this process and draw on both instrumental learning and fear extinction literatures to further our understanding of IL function.
Four experiments explored the role of IL in flexible behavior. Experiments 1a and 1b were instrumental learning experiments. Experiment 1a used a previously documented procedure to establish a single instrumental response as goal-directed in one context and habitual in another. Following reversible pharmacological inactivation of IL, goal-directed action was converted to habit, a novel finding. Experiment 1b expanded on this result by examining IL inactivation in an instrumental response that had received only minimal training in a single context. Here, IL inactivation had no effect, suggesting that IL is brought online by a multi-stage training history (i.e., action to habit).
Experiments 2a and 2b were fear conditioning experiments. Given the substantial literature regarding IL involvement in fear extinction, these experiments were intended to confirm the efficacy of our IL manipulation in the same rats from Experiments 1a and 1b, respectively. In both experiments, rats underwent contextual fear conditioning followed by two extinction sessions. Rats were then tested under IL inactivation either following extinction or following a subsequent reacquisition session in which the extinguished context was associated with shock again. In both experiments, IL inactivation impaired the expression of extinction learning. Although IL inactivation did not significantly affect the expression of reacquisition, the effect of IL inactivation depended on whether it was tested following extinction or reacquisition.
These results sketch the foundation of a framework in which IL is required to switch between available behavioral states when two conflicting things have been learned. The view may integrate the separately-studied roles of IL in instrumental habit learning and fear extinction learning.