Simultaneous TMS - EEG

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Bo
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Simultaneous TMS - EEG

Post by Bo » Mon Dec 07, 2009 5:05 pm

Hi to all

We recently started using online TMS while recording EEG data with the BioSemi Actiview system. We noticed that the amplifier is recovering from saturation rapidly during the first trials (around 20 consecutive trials of 1.5 secs each) and then suddenly passes to a very slow recovery (>600ms) for another series of around 20 trials, and so forth - good and bad recovery times in cycles. In other words, it is slowly getting into some sort of "long-term" saturation from which it needs long time to recover. Has anyone seen such a problem or has an idea of getting around it? May I be doing something wrong?
We are using a double pulse protocol with about 30ms between pulses. Can that be too much for the amplifier so I should better use just one pulse per trial? That leads me to a related problem - I also saw that the recovery from the second pulse is slow, whereas from the first it is rapid. Does that mean that double pulse is not suitable for the system?

I'd appreciate any tip!
Thanks

Bo

Coen
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Post by Coen » Mon Dec 07, 2009 6:47 pm

The usual cause of long recovery times is the CM going out of range during the pulse (blue LED off). The currents induced by the TMS pulses sometimes trigger the safety circuits, and this causes the AD-box to shut down the active electrodes temporarily. The problem can be solved by locating the CMS and DRL electrodes away from the area were the TMS pulses are applied. You may even want to locate CMS and DRL outside the headcap (use the flat CMS/DRL set)

Best regards, Coen (BioSemi)

Bo
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Post by Bo » Mon Dec 07, 2009 7:40 pm

Hi Coen,
Thanks for the answer!

What you are saying makes perfectly sense, and I admit that I did not think of it. I will try tomorrow playing with the location of the CMS-DRL.

Should I understand that a protocol of double pulse (lets say with 30ms between the two pulses) meets the abilities of the amplifier?

Have a good week,

Bo

Coen
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Post by Coen » Mon Dec 07, 2009 9:04 pm

The amplifier is DC. So long as the Common Mode remains in range, it should make no diffrence how long, or how many times the inputs are saturated.

Best regards, Coen (BioSemi)

Bo
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Post by Bo » Mon Dec 07, 2009 9:16 pm

OK we'll keep trying protocols,
Thanks very much, Coen

Bo

PaulS
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TMS/EEG

Post by PaulS » Wed Apr 07, 2010 5:11 am

Hi, I'm also interested in minimising TMS artifact. I would like to try as you suggest "locating the CMS and DRL electrodes away from the area were the TMS pulses are applied. You may even want to locate CMS and DRL outside the headcap (use the flat CMS/DRL set)."

Can you do this with the external CMS/DRL that plugs in via the circle connector? When I have tried this I get out of range errors presumably because there are now 2 CMS/DRL pairs: one on the head cap set (A) as well as the externals. How do you deal with this? Thanks. Paul

PaulS
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Location: MACCS

TMS/EEG

Post by PaulS » Wed Apr 07, 2010 5:48 am

Hi, I'm also interested in minimising TMS artifact. I would like to try as you suggest "locating the CMS and DRL electrodes away from the area were the TMS pulses are applied. You may even want to locate CMS and DRL outside the headcap (use the flat CMS/DRL set)."

Can you do this with the external CMS/DRL that plugs in via the circle connector? When I have tried this I get out of range errors presumably because there are now 2 CMS/DRL pairs: one on the head cap set (A) as well as the externals. How do you deal with this? Thanks. Paul

Coen
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Post by Coen » Wed Apr 07, 2010 1:59 pm

You are correct that only one CMS/DRL should be connected (or the CM will not come in range)

Purchase an A set without CMS/DRL, or remove the CMS/DRL form your current set (refer to http://www.biosemi.com/faq/split_cables.htm and cut off the 4 wires near the connector, be careful to not damage the isolation of the other wires).

Best regards, Coen (BioSemi)

ctischler
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Re: Simultaneous TMS - EEG

Post by ctischler » Thu Jul 27, 2017 7:28 pm

If anyone has tried using the flat CMS/DRL, could you report how the recovery time differed from the standard CMS/DRL? It would be much appreciated!

Thank you,
Claudia

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