EEG beta and gamma powers when comparing certain psychophysiological states with normal and weakened electromyogram of facial muscles

Abstract

The aim of the present study was to investigate EMG contamination on high-frequency scalp electroencephalogram (EEG) during comparisons of certain cognitive tasks performance. 19 healthy women who performed similar test tasks before and after cosmetic injections of Dysport in various face regions for reduction of facial muscles activity took part in the study. The test tasks were focused on induction of emotional states with different valences, on memory storing and extraction of verbal information. Default state of rest was uncluded too. During performance of the tasks, parallel registrations of EEG from a scalp surface(19 channels) and EMG from several facial muscles (6 channels) were carried out. Changes of spectral power in β2 and low γ frequency ranges (18-40 Hz) in EEG- and EMG-derivations after Dysport injections were analyzed. Changes of spectral power in the same derivations during comparisons of the different test tasks were analyzed before and after Dysport injections separately. It was demonstrated that Dysport injections lead to reduction of EMG power in regions of injections and to reduction of EEG power in frontal and temporal derivations. However, the EEG-correlates revealed when comparing different test tasks remain qualitatively invariable both after, and before Disports injections. These facts confirmed that EMG makes a noticeable contribution to the electric activity registered from a scalp in the frequency ranges more than 18-Hz. At the same time, it was shown that in certain experimental situations influence of EMG not necessarily interferes with identification of EEG-correlates of mental activity during EEG registration from a head surface in β2 and low γ frequency ranges.