New Technology Poster Session

Re: Poster 651

Risto Ilmoniemi

On Wed Dec 9, Katharina Kaspar wrote
>Dr. Ilmoniemi: Hope you are enjoying the meeting. A very interesting poster. What methods were used to eliminate the artefacts by the TMS pulses?
We had to deal with 4 kinds of artefacts.
1) The TMS pulse induces a voltage between the electrode leads, which can saturate the EEG amplifiers. To overcome this artefact, the electronics was designed so that the output voltage remained fixed during the pulse (which lasts less than 1 ms). A sample-and-hold technique was used.
2) Special electrodes, with slits to avoid large metallic loops, were used to avoid strong forces due to the TMS pulses from causing an electrode-movement related artefact.
3) Artefacts from the activation of the skin were dealt with also by the sample-and-hold technique (hold time on the order of 10 ms, depending on the stimulated scalp site)
4) Auditory artefacts were dealt with using a subtraction technique (Response to TMS sound subtractes from the response to the TMS and the sound together)

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