Neural network organization of the cognitive map

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The aim of the proposed studies was to investigate functional neuronal organization related to either spatial or episodic memory and to further determine whether these changes are site- (hippocampus vs neocortex) and time- (short- vs long-term) dependent. Previous studies from our laboratory demonstrated that for a spatial task, there is a cluster-type neuronal organization that occurs in the hippocampus. The first study was aimed at determining whether a similar organization also exists for episodic memory. We trained mice (n=5) to perform to 80% criterion in an episodic memory task, while control mice (n=4) retrieved food randomly (no memory demand). The brains were then processed for immunohistochemistry for the activity-dependent immediate-early gene zif268. Preliminary analysis of the results appear very promising. We are currently replicating this experiment to increase the number of subjects and to obtain more conclusive results. For episodic memory, the hippocampus is initially involved (24h) while at longer time intervals (30d) neocortical structures are activated. At the completion of the above study we will perform a second experiment to determine whether the long-term storage of spatial memory is also dependent on activation of neocortical structures.