EMG artifact

Contamination from skeletal muscle. Cranial, neck, jaw and facial muscles generate broadband electromyographic activity whose power rises through the 20 to 300 Hz range and peaks well above the EEG band, but with substantial spectral overlap onto the beta and especially gamma ranges that BCIs increasingly exploit. Even sub-visible tonic muscle tone, clenching, swallowing or speaking injects spatially focal, high-frequency variance at temporal and frontal electrodes.

EMG is the most treacherous artifact for high-frequency analysis because it masquerades as neural high-gamma: it is broadband, non-stationary and shares the same time course as task engagement, so averaging does not remove it and a claimed gamma effect can be pure myogenic contamination. Mitigation combines electrode placement away from muscle, spatial filtering (ICA, canonical correlation analysis, source separation), and — for cortical high-gamma claims — control analyses (bipolar or Laplacian montages, EMG monitoring, or invasive recording) to prove the signal is cerebral.