Event-related potential map differences depend on the prestimulus microstates.

The dependency of the landscapes of visually evoked, 47-channel, event-related potential (ERPs) on the functional microstates (momentary map landscape) just before stimulus arrival was investigated, in 12 volunteers. The prestimulus microstates were determined using the map at the last peak of Global Field Power before the stimulus. The landscapes of these maps were described by the electrode locations of the positive and negative extreme potentials, and assigned to basic classes. The two most frequently occurring map-classes were used (left anterior-right posterior, and right anterior-left posterior). ERP map series were averaged for each subject and each prestimulus microstate class. The Randomization-Monte Carlo MANOVA test was used to test the significance of the difference between the ERP map landscapes at each sample point (n = 128, 500 ms) associated with the two prestimulus microstates. At 16 samples the difference was significant at p < 0.05. The longest uninterrupted sequence (n = 9) of significant differences occurred between 164 and 195 ms, i.e. during the conventional component P200. The results demonstrate that the brain electric microstate at stimulus arrival crucially influences the active neuronal populations that contribute to the ERP. This suggests that the processing of information will differ as a function of the momentary brain microstate at information arrival.