Prefrontal Cortical Contributions During Discriminative Fear Conditioning, Extinction, and Spontaneous Recovery in Rats

This research examined the roles played by the ventromedial orbital prefrontal cortex (OPFC) and the infralimbic/prelimbic prefrontal cortex (I/P PFC) during discriminative fear conditioning. The first experiment included nine rats with bilateral lesions to the I/P PFC, an additional nine with OPFC lesions, and eight sham lesion controls. Behavioural analysis was conducted using a discriminative fear conditioning to context task 10 days after surgery. Results indicate that lesions to ventromedial orbital prefrontal cortex result in generalized fear and impaired extinction. In contrast, infralimbic/prelimbic cortical lesioned animals exhibit appropriate fear response patterns and extinction, but show a specific impairment in spontaneous recovery. To ascertain why I/P PFC lesion rats did not exhibit spontaneous recovery, a second experiment was conducted. All procedures in the second experiment were identical to the first except a decay period was employed in place of extinction training. Results from the second experiment indicate that the difficulty retrieving the extinguished association is related to extinction processes and not decay. Taken together, these findings suggest that OPFC and I/P PFC have distinct roles in associative processes necessary for discriminative fear conditioning, extinction, and spontaneous recovery. These results further implicate OPFC and I/P PFC in the pathology underlying generalized anxiety disorder.