The Contribution Of The Time Locking Of Eec Waves To The Generation Of The Auditory P300

Objectives: To study the time locking of the ‘natural’ (delta, theta, slow alpha, fast alpha and beta) EEG waves during the generation of the P300 in passive (P300a) and active (P300b) auditory oddball paradigms in order to obtain insights into the generation of the P300 and into the transitions between background and evoked activity. Methods: Tone burst stimuli (standard and deviant) were delivered to normal young adult subjects in passive and active oddball paradigms. The time distributions of EEG waves were analyzed in several frequency bands during background and post-stimulus periods. Results: The ongoing background activity was modified by the deviant stimulus, producing the time locking of the positive delta, theta and alpha EEG deflections in the time range of the P300. This involved prolongation of the positive component of negative-positive wave complexes so that the positive wave was delayed into the time period of the P300. The time locking effects were more prominent in the delta and theta ranges, and differed in frequency components and scalp topography between the two paradigms. Not all deviant stimulus trials contributed deflections to the P300. The contributing trials can be selected, providing the basis for single trial analysis. Conclusions: The study of the time locking of the EEG waves in different frequency bands provides improved analysis of the P300 and an approach to single deviant stimulus trial analysis, that in turn can enhance signal-to-noise ratios. The results show that the time reorganization of EEG can be considered in the generation of P300 separately from the amplitude factor. Significance: This can lead to improved analysis of normal and abnormal brain function in individual subjects.