Unfolding the cognitive map: The role of hippocampal and extra-hippocampal substrates based on a systems analysis of spatial processing.

What has been long absent in understanding the neural circuit that supports spatial processing is a thorough description and rigorous study of the distributed neural networks associated with spatial processing-both in the human as well as in rodents. Most of our understanding regarding the elucidation of a spatial neural circuit has been based on rodents and therefore the present manuscript will concentrate on that literature. There is a trend emerging in research to expand beyond the hippocampus for evaluating spatial memory, but the thrust of the research still focuses on the role of the hippocampus as essential and other neural substrates as performing sub-servient roles to support hippocampus-dependent spatial processing. This review will describe spatial memory in terms of a system model incorporating partially overlapping and interacting event-based, knowledge-based and rule-based memory systems that are composed of different component processes or attributes associated with spatial processing which are mapped onto the corresponding neural substrates and larger networks. In particular, the interactions among brain systems that process spatial information will be emphasized. We propose that these interactions among brain regions are essential for spatial memory.