Involvement of Cortical Associative Areas in Acquisition and Retrieval of Delayed and Traced Conditioned Fear in Mice.

Associative learning is a universal mechanism for acquiring new experience; it can be modeled in animals using fear conditioning (FC). Based on the temporal relationship between the conditioned and unconditioned stimuli, two paradigms of FC are distinguished: delay FC (dFC; where the unconditioned stimulus is presented concurrently with the conditioned one) and the more complex trace FC (tFC; characterized by a gap between the conditioned and unconditioned stimuli). In this study, we compared the activity of associative neocortical areas during the formation and retrieval of memory in these paradigms. Animals successfully acquired both forms of FC; during tFC training, c-Fos expression was observed in the parietal associative cortex. However, neither the parietal associative cortex nor the retrosplenial cortex was activated during memory retrieval in tFC. In contrast, both areas were activated during memory retrieval in dFC. These results provide the first evidence of the differential involvement of parietal associative cortex in the formation and retrieval of different forms of associative memory.