Inactivation of the infralimbic prefrontal cortex reinstates goal-directed responding in overtrained rats

Abstract

Over the course of extended training, instrumental responding in rats shows a transition from goal-dependent performance to goal-independent performance, as assessed by sensitivity to reward-devaluation induced by taste aversions or specific satiety. It has been suggested that this reflects the gradual dominance of reflexive, habit-based responding over voluntary, goal-directed actions. Previous research suggests that lesions of the medial prefrontal cortex disrupt this interaction between goal-directed and habitual responding. More specifically, whereas lesions of the prelimbic prefrontal cortex appear to disrupt normal goal-directed responding, lesions of the infralimbic prefrontal cortex cause animals to remain goal-directed even after substantial overtraining. The current experiment explored further the nature of this interaction between actions and habits. Rats were given extended training of an instrumental lever press response before bilateral intracerebral cannulae giving access to the infralimbic cortex were implanted. Following further reminder training all animals were given a test of goal sensitivity by specific-satiety devaluation of the instrumental outcome, or a matched reward, prior to extinction tests. Before these tests, half of the animals received bilateral infusions of muscimol into the infralimbic cortex, and the remainder, control vehicle infusions. As expected after extended instrumental training, control-infused animals showed habitual performance that was not selectively influenced by devaluation of the instrumental outcome. In contrast, animals receiving temporary inactivation of the infralimbic cortex by muscimol showed selective sensitivity to devaluation of the instrumental outcome, indicating a reinstatement of goal-directed responding in these animals. This suggests that the development of habitual responding reflects the active inhibition of goal-directed responses that are mediated by action-outcome associations.