Practical digital filters for reducing EMG artefact in EEG seizure recordings

In long-term scalp EEG monitoring of epileptic patients it is virtually impossible, in the present state of the technology, to avoid movement-related artefacts. These often obscure EEG information about the location of the seizure focus. One important example of such artefact is EMG activity. Its removal or suppression is sometimes enough to make otherwise useless EEG traces readable. Different methods of filtering have been applied towards that end. We routinely use a 15 Hz setting on our polygraph in obtaining EEG seizure printouts. We have recently examined digital filters which attenuate EMG beyond what is possible with the 15 Hz filter. A concern has been that the filters are practical in that they run in real time on a simple microprocessor and cause a minimum of confusion between smoothed artefact and actual brain activity.