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Biosemi for recording motor-evoked potentials

Posted: Wed Mar 27, 2013 1:49 pm
by Erman

I have been using a Biosemi system to record motor-evoked potentials (MEPs) using TMS. Active electrodes on the FDI muscle of the right hand record the MEPs. I have been recording at 2048Hz sampling rate (speed mode 4).

Could I ask what the hardware filter settings are set at with this kind of sampling - particularly the high end of the bandpass?

The MEPs currently recorded look a little strange. If you look at the attachment of what a normal MEP should look like (normal_MEP.jpg) and compare it to the MEPs I have been getting (myMEP.jpg), there are some differences. For example, the waves that should be present just after the MEP are entirely absent in my MEP. This seems like it might be an issue with filtering.

Finally, after some TMS pulses in the raw data, the signal also struggles to return to baseline following the TMS pulse artefact. I wonder if this is also likely to be a product of amplifier settings, or some kind of interaction between the TMS pulse and the amplifier?

Any help would be enormously appreciated.

Thank you,

Re: Biosemi for recording motor-evoked potentials

Posted: Thu Mar 28, 2013 11:42 am
by Coen
ActiceTwo does not show the filter ringing problem seen in the "normal" MEP. For filter info, see viewtopic.php?f=1&t=351

ActiveTwo is a DC system, return to baseline after overload takes 5 samples (due to FIR filter in ADC). Increased baseline return time after (several) TMS pulses is almost surely caused by electrode polarization (provided Common Mode remains in range during the pulse, blue LED should remain ON).

Best regards, Coen (BioSemi)

Re: Biosemi for recording motor-evoked potentials

Posted: Thu Jul 27, 2017 7:03 pm
by ctischler
As a follow-up to the question regarding recovery time, if it takes 5 samples to recover, does that mean increasing the sampling rate will allow for faster return to baseline? I am trying to figure out how to measure the peak-to-peak MEP amplitude while I deliver TMS over M1 and record from EEG.

Thank you in advance for your help,

Re: Biosemi for recording motor-evoked potentials

Posted: Fri Jul 28, 2017 11:36 am
by Coen
A higher sample rate does indeed result in faster pulse response. This will mean faster return to baseline in practical measurements provided that the amplifier response is the limiting factor. This is usually not the case with TMS, where the return to baseline speed is usually determined by electrode polarization effects (see TMS threads). So changing the sample rate won't have an effect.

Best regards, Coen (BioSemi)