Alpha oscillations as an indicator of dynamic memory operations - anticipation of omitted stimuli

Elaborating on a paradigm of Basar in experiments with periodically present ed auditory or visual stimuli, 10 subjects performed tasks in which omitted stimuli had to be anticipated and their (virtual) onset time had either to be marked (a) mentally ('mental marking' MM) or (b) by pressing a button ( 'button pressing' BP). EEG was obtained from 11 sites in frontal, central, temporal, parietal and occipital areas. The experiments were carried out in triplets of MM, BP, MM measurements. Mean temporal errors of motor respons es served as the basis for a functional interpretation of EEG patterns. Cor relation analysis of sweeps for each individual revealed brief intervals of phase ordering of EEG patterns in the alpha range lasting approximately th ree periods. For frontal and vertex derivations a close congruence of the l ocation of the phase-ordered patterns to mean errors of motor responding wa s shown. These results corroborate the claim that 'emitted' alpha oscillati ons represent intentional processing. The close agreement between temporal locations of phase-ordered EEG segments and these of the motor responses st rongly suggests that EEG phases represent memory retrieval of period durati on as a common functional component of MM and BP. A lack of topographical c orrespondence with results from a passive 'missing stimulus' paradigm under lines the specific intentional origin of the observed phase ordering. Theor etical implications of the results are discussed. (C) 2000 Published by Els evier Science B.V. All rights reserved.