Event-related oscillations are 'real brain responses' - wavelet analysis and new strategies

The EEG consists of the activity of an ensemble of generators producing rhy thmic activity in several frequency ranges. These oscillators are active us ually in a random way. However, by application of sensory stimulation these generators are coupled and act together in a coherent way. This synchroniz ation and enhancement of EEG activity gives rise to 'evoked' or 'event-rela ted oscillations'. The compound evoked potential manifests as superimpositi on of evoked rhythms in the EEG frequencies ranging from delta tio gamma (' natural frequencies of the brain'). The superimposition principle is descri bed with efficient strategies and by utilization of an efficient algorithm. The wavelet analysis confirms the results of the combined analysis procedu re obtained by using the amplitude frequency characteristics (AFCs) and dig ital filtering. The AFC and adapted digital filtering methods are based on the first approach to analyze average evoked potentials. In contrast, the w avelet analysis is based on signal retrieval and selection among a large nu mber of sweeps recorded in a given physiological or psychological experimen t. By combining all these results and concepts, it can be stated that the w avelet analysis underlines and extends the expression that alpha-, theta-, delta-, and gamma-responses described In this report are the most important brain responses related to psychophysiological functions. The wavelet anal ysis confirms once more the expression 'real signals' which we attribute to EEG frequency responses of the brain. It will be demonstrated that the del ta, theta, and alpha responses (i.e. the rhythms 'predicted' by digital fil tering) are real brain oscillations. The frequency components of the event- related potential vary independently of each other with respect to: (a) the ir relation to the event; (b) their topographic distribution; and (c) with the mode of the physiological measurements. (C) 2001 Elsevier Science B.V. All rights reserved.