THE EFFECT OF PRE-STIMULUS ALPHA-ACTIVITY ON THE AUDITORY P300 PARADIGM - A PROSPECTIVE-STUDY

A method is described for carrying out Evoked Response Potential (ERP) testing in which the background EEG is itself treated as an independe nt variable, and the application of a stimulus made contingent upon th is variable. As an illustration of the method, an Auditory Oddball par adigm was implemented, in association with real time processing and te sting of the background EEG, and an investigation was carried out into the effect of background alpha activity in 35 normal subjects. In the novel methodology presented here, stimulus presentation was condition al on a ''high'' level of alpha activity in the pre-stimulus EEG as ev aluated by real-time spectral analysis. The dependency of presentation of the stimuli on the state of the pre-stimulus EEG suggests the term ''interactive'' ERP for the methodology. The resulting ERP was compar ed with that of a matched recording without pre-stimulus EEG testing. The results show that the parietal P300 peak is reduced by the use of alpha dependent recording. This result indicates that the background E EG activity at the time of application of a stimulus can have an effec t on the resulting ERP.