Prefrontal cortex subregions and their involvement in the acquisition and extinction of conditioned fear
The prefrontal cortex (PFC) has been implicated in emotional processes in both humans and in rats. The exact role it plays and the contributions of its various subregions have not been well defined. Four studies were conducted to assess the role of rat PFC subregions in the acquisition and extinction of fear conditioned to contextual stimuli and to an explicit conditioned stimulus (CS). In the first two studies, lesions of ventral medial PFC (mPFCv) resulted only in prolonged responding to the CS during extinction, while lesions to the dorsal portion (mPFCd) resulted in increased freezing to both the context and CS during both acquisition and extinction. In the third study, lesions of the ventrolateral PFC resulted only in reduced contextual conditioning. In the final study, post-training lesions of mPFCv reduced contextual conditioning and eliminated the original (study 1) prolonged extinction effect. They further facilitated re-learning of the same task, and prolonged responding during re-extinction beyond the level expected from the amount of facilitation in relearning. As a whole, these results suggest a functional heterogeneity within rat PFC. They further suggest that mPFCv plays a role in the extinction of conditioned fear somewhat independent of initial fear levels, and may do so by being involved in the inhibition of conditioned responding when the response is no longer appropriate.
0384: Behaviorial sciences