Identical responses of the two hippocampal theta generators to physiological and pharmacological activation

The possible existence of two separate RSA generators in the dorsal hippocampus raises questions as to the degree of coupling or independence of both. In order to answer these questions bipolar EEG recording were made in the CA1 and dentate gyrus of freely moving rats during conditions of RSA generation by different manipulations. The quantitative EEG parameters of simultaneous records were compared and cross correlation functions were calculated. Results indicate that even under different conditions of inducing RSA (physiological activation or injection of arecoline and nicotine) yielding RSA with different frequency characteristics, the quantitative EEG parameters were similar in both recordings. In addition, a high degree of concordance of both EEG was evidenced in the cross correlation function. These observations are discussed in terms of a high degree of coupling between both RS generators.