Probability interrelations between pre-/post-stimulus intervals and ERD/ERS during a memory task.

OBJECTIVES To investigate the functional relationship between oscillatory electroencephalographic (EEG) components (pre-/post-stimulus intervals) with audio-event-related desynchronization/synchronization (ERD/ERS). METHODS In an experimental study (9 subjects), the probability-classification analysis of single-trial spectral EEG changes was utilized. Results were compared with auditory ERD/ERS. RESULTS It was shown that (1) variability of EEG spectral patterns was considerable, (2) EEG activity was different at various task stages, (3) probability measures were different from the results of conventional frequency analysis, (4) probability of trials with alpha- and theta-patterns was characteristically different in various task stages, (5) the occurrence of alpha- and theta-trials were most probable, but not frequent enough to characterize all the trials. The results suggest that the ERD/ERS responses are influenced by EEG characteristics in the pre-stimulus interval, which also have a strong influence on the EEG in the post-stimulus interval. CONCLUSIONS Alpha- and theta-ERD/ERS responses during memory task performance are not typical for all trials. They reflect EEG changes only in approximately 39% for alpha-activity and approximately 43% for theta-oscillations of all trials, what reflects piecewise stationary EEG structure.