The hipporcampus has an as yet undetermined, but critical involvement in the process of formation of long term memory. The current view suggests that the hippocampus indexes rather than sotres new memory items, thus making them available for retrieval and for einforcement in the necortex (Teyler & Discenna, 1986). The hippocampus is also known to function as a spatial representatio system. IN rodents, on which many of the hipporoampal studies were conducted, the firing of most hippocampal principal cells (called place cells) during maze running is specific to the current location of the animal, regardless of the immediate availability of any location-specific sensory information (O'Keefe, 1979; O'Keefe & Conway, 1980) (Fig. 1). This fact suggests that the hippocampus implements an internal dynamical model of the a nimal's world, called a cognitive map by O'Keefe and nadel (1978). This concept of a cognitive map is widely accepted in the field of spatial memory studies. Given this framework, one can think of the hippocampal cognitive map as the indexing set for episodic memory (Nadel et al., 1985; McNaughton et al., 1996). The present work is concerned with the critical issue of this big problem: understanding the organization and the dynamcis of the hippocampal cognitive map. The rodent spatial cognitive map is studied here as a particular case, because of the exclustive availability of experimental knowledge in this case.
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