Morphology and dynamic repertoire of EEG short-term spectral patterns in rest: Explorative study

In the present explorative experimental study, we examined the diversity of electroencephalographic (EEG) short-term spectral patterns (SPs) within a broad frequency band (1.5–30 Hz) for healthy adult subjects during closed eyes and open eyes resting conditions. The types of EEG SPs were assessed by counting all identical SPs with peaks in the same frequency bins from the pools of SPs, which were built from all the SPs of the entire EEG signal (all locations) for all subjects separately for closed and open eyes conditions. This study demonstrated that independently of the resting functional state of the brain (closed eyes vs. open eyes) (a) the diversity of short-term EEG SP types was limited, (b) the percent distribution of SP types among different categories of SPs (based on morphology of SPs) was constant and (c) the most preferred frequencies were restricted to delta–theta and alpha bands. At the same time, closed eyes and open eyes conditions differed from each other by the percent distribution of different types of SPs. The probabilities for the occurrence of particular SP types were typical for each of the examined conditions with domination of alpha–rhythmical SPs during closed eyes condition and domination of delta–theta–rhythmical SPs during open eyes condition. The findings suggest that the diversity of SPs varies as a function of functional state of the brain during resting conditions. Understanding of the diversity of short-term EEG SP types is important theoretically and practically, and is significant for advancing the interpretation of the EEG signal.