On the evoked mass-potential in relation to electrical background activity in the rabbit

The relationships between the response configurations of evoked potentials and background EEG activities were investigated from the autocorrelogram and “response amplitude-frequency diagram” by using unanesthetized, immobilized rabbit.Autocorrelograms of EEGs in the arousal state during repetitive flas h stimulation showed an increase of regularity and decrease of noise elements in the amplitudes of the evoked potentials. This elevated brain activity level means the increased acuity and clarity of sensory informations.From the response amplitude-frequency diagram during repetitive lateral geniculate (GL) stimulation, the concentrating-accelerating tendency by arousal were evident in the activities of specific origin. That is to say, with change in the background EEG from sleep to arousal, every component of the cortical potentials evoked by GL stimulations of various frequencies were augmented and especially the responses to only one or two stimulating frequencies were found to show a concentrating increase. These frequencies correspond to the characteristic frequency in the specific system demonstrated in the previous paper (MIMURA et al., 1967). On the other hand, the responses to repetitive reticular (RF) stimulations of various low frequencies retained their irregularity in the response diagrams and, contrary to GL stimulation, their amplitudes were decreased due to arousal EEG. Peripherally induced responses to repetitive flash stimulation exhibited a very complicated behavior in their augmentative and depressive tendencies with change of background EEG, suggesting mixed or summated features due to both augmentative specific activities (by GL stimulation) and depressive non-specific activities (by RF stimulation).The spontaneous regular EEG wave in arousal was discussed from the resemblance of frequencies in relation to the activity changes of the evoked potential.