Hippocampal theta rhythms from a computational perspective: code generation, mood regulation and navigation.

In this paper three computer models are summarized discussing different functions of the cortico-hippocampal system. Mood regulation, rhythm and code generation and navigation are integrated into a coherent conceptual framework around the concepts of structural hierarchy and circular causality. First, a model of spatio-temporal code generation is reviewed in which the hippocampal population theta rhythm plays an important role. Next, generation and pharmcological modulation of this rhythm is examined using a computer model of multiple cell populations forming a feed-back loop within the hippocampus and between the septum and the hippocampus. Last, an abstract, but biologically motivated model of navigation is described which achieves a near optimal mode of navigation by composing hierarchical levels of the cortico-hippocampal system. The connections among the different hierarchical structures of the cortico-hippocampal organization and their functional roles are discussed.