An investigation of hippocampal theta rhythm of rats as a nonlinear dynamic process.

The results of an investigation of the hippocampal theta rhythm of rats in the paradoxical phase of sleep and during orienting behavior by the method of estimation of attractor dimension are presented in this article. It has been demonstrated that the hippocampal theta rhythm consists of a regular constituent and an irregular constituent of high dimension, the interrelationship of which varies within wide limits depending upon the state of the animal. Frequency components of the regular and irregular constituents were identified. The mechanisms of their formation are considered and some hypotheses regarding their biological nature are proposed.