Basically EEG signals (potential from brain) contain 'noise' due to EMG signals (potential from muscles). I was thinking of using the EMG as a common mode feedback prior to the amplification of the EEG signal. Thus, I would assume the EMG signal (EEG 'noise) can be removed when it enters the differential amplifier.

I am just wondering how possible this is. I am aware that EMG signals are much larger than EEG signals.

  • \$\begingroup\$ I think this needs the EMG embedded in the EEG is the exact same as the EMG you're using as a reference. Is this the case? \$\endgroup\$ – Los Frijoles Apr 19 '18 at 2:13
  • \$\begingroup\$ Normally muscle noise is reduced on scalp with gavlanic noise and variable capacitance from lack of pressure By using silver oxide pads with pressure such as a baseball cap. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Apr 19 '18 at 2:25
  • \$\begingroup\$ @Los Frikoles That's correct, The EEG and EMG system is identical, the only difference is the EMG electrodes are mounted directly to the 'noise' source, while the EEG is mounted in the scalp containing the required signal with the noise too. \$\endgroup\$ – Nathan Le Apr 19 '18 at 2:30
  • \$\begingroup\$ @TonyStewartEEsince1975 So a stretchy rubber hemisphere that pushes the electrodes on to the scalp would be called a Vari-Cap? \$\endgroup\$ – Henry Crun Apr 19 '18 at 2:56
  • \$\begingroup\$ or a Howie Mandel latex cap \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Apr 19 '18 at 3:00

No -- sounds like a good idea, but separating EEG and EMG is much easier said than done. How do you intend to get "pure" EMG to use as your common Mode signal, especially if it shares a freq spectrum with EEG?

The real way to separate emg and eeg is filtering. EEG is lower frequency than EMG. What isn't low frequency, though, is movement artifact. If the EMG activity is caused by movement, and the movement also causes motion in the electrode-skin interface, this can cause trouble.

  • \$\begingroup\$ Yeah that's what I'm a little unsure about. I was maybe thinking that since the EMG signal is significantly larger than the EEG signal that it would be 'pure' enough. Is their any way I can set up a basic setup showing this. This is for my final year research study. \$\endgroup\$ – Nathan Le Apr 19 '18 at 2:35
  • \$\begingroup\$ @NathanLe my comment is your answer. Suppress the noise by better sensing the physcial contacts with pressure and lower resistance. The best signals require shaving hair and abrasion, but I don't think it is necessary. Analyze the pad C and shunt R time constant to get RC<< 1 s with low ESR on contact \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Apr 19 '18 at 2:38
  • \$\begingroup\$ @Tony Stewart Thanks for your reply. However I was looking for some sort of original approach related to this setup for study for my research project \$\endgroup\$ – Nathan Le Apr 19 '18 at 2:41
  • \$\begingroup\$ This is how I did it successfully this way with a good INA about 44 yrs ago, how far back did you want to go? RL CM feedback is also used. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Apr 19 '18 at 2:43
  • \$\begingroup\$ No I believe you that it's a proven method to use. But that is my point. For the purpose of my project, I wanted to talk about my approach of using 'EMG's as a common mode feedback for noise reduction' because it doesn't seem to have been done before. (I can discuss about the effectiveness etc. in my results evaluation) \$\endgroup\$ – Nathan Le Apr 19 '18 at 2:45

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