Involvement of the bed nucleus of the stria terminalis in initial conditioning and rapid reconditioning following extinction of contextual fear.

Although a great deal is known about neurobiological mechanisms of initial conditioning and extinction, relatively little is known about mechanisms involved in the return of behavior following extinction. In this article, we examine the effects of temporarily inactivating the bed nucleus of the stria terminalis (BNST) on initial conditioning and postextinction reconditioning. We investigate effects in unsignaled contextual fear conditioning, in which animals initially receive strong contextual conditioning, followed by three sessions of nonreinforced context exposure (extinction), and then receive a single context-shock reconditioning trial. In 2 experiments with male Long Evans rats, we evaluated the effects of delivery of a muscimol/baclofen cocktail to the BNST prior to initial conditioning or reconditioning. In Experiment 1, we found that a single context-shock pairing results in more freezing following extinction than when it is the initial conditioning trial. This rapid reconditioning effect was impaired by BNST inactivation. In Experiment 2, we found that BNST inactivation also causes a deficit in freezing after strong initial conditioning. These findings suggest that the BNST is involved in both initial conditioning and postextinction reconditioning. We discuss implications of these findings for current thinking about BNST function in learning and memory processes.