Encoding and retrieval are differentially processed by the anterior cingulate and prelimbic cortices: a study based on trace eyeblink conditioning in the rabbit.

A growing body of literature suggests that structures along the midline of the prefrontal cortex (mPFC), including Brodmann's area 32 (prelimbic cortex) and area 24 (anterior cingulate cortex) in the rabbit play a role in retrieval of learned information. The present studies compared the effects of post-training lesions produced either immediately or 1-week following learning, to either prelimbic (area 32) or anterior cingulate (area 24) cortex on trace eyeblink (EB) conditioning. Further, because recent evidence suggests that the mPFC may play an even greater role in learning and memory when emotional arousal is low, these studies compared the effects of lesions in groups conditioned with either a relatively low-arousal corneal airpuff, or a more aversive periorbital eyeshock unconditioned stimulus (US). A total of six groups were tested, which received selective ibotenic acid or "sham" control lesions to either area 32 or 24, immediately or 1-week following asymptotic learning, and conditioned with an eyeshock US or an airpuff US. Results showed that the greatest lesion deficits were found when conditioning with the less aversive airpuff US. Further, lesions produced to area 32 one-week, but not immediately following learning, caused significant deficits in performance, while lesions produced to area 24 immediately, but not 1-week following learning, caused significant deficits in performance. These findings add to the body of evidence which shows that area 32 of the mPFC regulates retrieval, but not acquisition or storage of information, while area 24 mediates a less specific reacquisition process, but not permanent storage or retrieval of information during relearning of memories abolished by mPFC damage. These findings were, however, specific to those experiments in which the relatively non-aversive airpuff was the US.