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EEG artefacts: 'mind' or just muscle activity?

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Published on Jun 20, 2013

It is important to be able to distinguish between EEG and, for example, muscle activity in times where people claim to read the 'mind' but often just register facial muscle activity or eye movements.

Muscle activity (EMG) is in the region of 1mV whereas EEG is in the region of 10uV, thus 100 times smaller. Both, EEG and EMG cover similar frequency ranges. Both, EEG and EMG are hard to control consciously. Electric fields from the surrounding area such as mains cables induce voltages in the cables of about 100mV and therefore about 10,000 times stronger than any EEG. Ideally the differential amplifier takes care of these influences but when moving around this is not 100% accurate so that movement artefacts might look like slow EEG waves. Eye movements are the third problem which have also pretty high amplitudes in the region of 1mV.
Overall EMG is the main problem because it is always there (except in totally paralysed patients) and it is tricky (though not impossible) to gauge what is EMG and what is EEG. Ideally it requires a subject to consciously minimise their EMG and at the same time is able to control their EEG.
Presenters: Vasso Georgiadou & Cat MacLeod
http://biosignals.berndporr.me.uk

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