Contrasting networks for recognition memory and recency memory revealed by immediate-early gene imaging in the rat

摘要

The expression of the immediate-early gene c-fos was used to compare networks of activity associated\udwith recency memory (temporal order memory) and recognition memory. In Experiment 1, rats were first\udfamiliarized with sets of objects and then given pairs of different, familiar objects to explore. For the\udrecency test group, each object in a pair was separated by 110 min in the time between their previous\udpresentations. For the recency control test, each object in a pair was separated by less than a 1 min\udbetween their prior presentations. Temporal discrimination of the objects correlated with c-fos activity in\udthe recency test group in several sites, including area Te2, the perirhinal cortex, lateral entorhinal cortex,\udas well as the dentate gyrus, hippocampal fields CA3 and CA1. For both the test and control conditions,\udnetwork models were derived using structural equation modeling. The recency test model emphasized\udserial connections from the perirhinal cortex to lateral entorhinal cortex and then to the CA1 subfield. The\udrecency control condition involved more parallel pathways, but again highlighted CA1 within the\udhippocampus. Both models contrasted with those derived from tests of object recognition (Experiment 2),\udbecause stimulus novelty was associated with pathways from the perirhinal cortex to lateral entorhinal\udcortex that then involved both the dentate gyrus (and CA3) and CA1 in parallel. The present findings\udimplicate CA1 for the processing of familiar stimuli, including recency discriminations, while the dentate\udgyrus and CA3 pathways are recruited when the perirhinal cortex signals novel stimuli.