MEG and EEG show different sensitivity to myogenic artifacts

Simultaneous measurements of EEG, MEG and EMG were performed during randomized blocks with higher and lower muscular stress in comparison to baseline condition. Power spectral density PSD was analyzed separately for five intervals (theta, delta, alpha, beta, gamma). During increased muscular stress, a significant increase could be observed in most bands of EEG while MEG showed no significant changes. Topography of maximum effects for the EEG render cortical generators implausible and point instead to myogenic sources. This was confirmed by correlating changes in EEG with those in EMG. During reduced muscular stress, only gamma activity of the MEG showed significant amplitude reduction. Modeling myogenic activity, its portion could be estimated to be approximately 10 percent in the spontaneous MEG brain signal.