Power spectra of cortical electric activity in the rabbit in relation to conditioned reflexes

In chronic experiments on rabbits spectral and correlation characteristics of cerebral cortical potentials were computed to study the elaboration of a conditioned defense reflex. was found that the frequency spectra of the EEG are subject to consistent changes: a narrow-band frequency constantly developing in the theta range. During exposure to a positive conditioned stimulus, the maximum of this frequency increased relative to the pre-stimulus period and a maximal coherence of electrical processes was observed in a narrow theta range between the electrical processes of the cortical analyzers to which the conditional and unconditional stimuli were addressed. Different relationship was noted in the theta range during presentation of a differential or extinguishing stimuli: it became slightly slower than in the pre-stimulus period, and the coherence of the theta rhythms was less than maximal, remaining high at the other frequencies. It was concluded that the presence of highly coherent electrical processes in the theta range is important for the formation of conditioned reflex in the rabbit cerebral cortex. The processes of internal inhibition are characterized electrographically by disagreement of electrical processes in the theta range in respect to phase or frequency.