Flexible navigation in the real world involves the ability to maintain an ongoing estimate of one's location in the environment, to use landmarks to help navigate, and to construct shortcuts and paths between locations. In mammals, these functions are believed to be performed by a circuit that includes the hippocampus and associated cortical areas. The physiological characterization of the neural substrates for navigation has progressed rapidly in the last 4 decades, together with plausible

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... anistic models for the generation of such activity. However, questions about how the various components of the circuit interact to perform the overall computations that account for the navigational ability of mammals remain largely unsolved. We review physiological and anatomical data as well as models of hippocampal map building and self-localization, to establish what is understood about the brain's navigational circuits from a computational perspective. We discuss major areas where our understanding is incomplete.