[Analysis of the segmental structure of EEG alpha-activity in humans]

Phasic organisation of human EEG alpha activity was studied in a pilot investigation using a previously suggested EEG segmental analysis methodology. The EEG was recorded in three normal subjects under resting conditions. The segmentation procedure enabled effective identifying of the periods with different amplitude in alpha band and the short-term transitions between them. Mean intersegmental variability of amplitude envelope were computed for the eyes closed and eyes open EEG in each of 16 standard derivations. Analysis of segment amplitude distributions showed that the difference between the average alpha activity amplitude in these conditions were determined mainly by variations in the number of segments of different amplitude classes and not by a shift of the distribution or by change of its width. Distribution and quartile analysis of mean segment amplitudes provide evidence for possible functional heterogeneity of upper and middle subranges of the amplitude range.