[The theta rhythm of the rat hippocampus as a nonlinear dynamic process]

The theta rythm of the rat's hippocampus in paradoxical phase of sleep and in orientational behavior is investigated by estimating the attractor's dimension. It is shown that the theta rhythm of the hippocampus consists of a regular component and an irregular one of high dimension which relation is in the wide variation depending on the state of the animal. The frequency characteristics of both components are revealed as well as the mechanisms of their forming. Some hypothesis that concern their biological nature are suggested.