[Eeglablist] EEG/ERP and TMS

Fri May 30 12:20:28 PDT 2003

The scenario you described is of course possible and that's why
designing the cut-off circuit is not a trivial task. It apparently took
the Finnish group a number of years to get it to work. I didn't work
with the system myself but I have a dataset I got from Ilmoniemi's lab
and it looks really clean. You can't even see the part that was cut if
you look at it at standard resolution. Only if you zoom in you see a
flat segment 7 ms long. There are no disturbances seen in single trials
after the reconnection. If you want to know the technical details of how
this is done I'm not the one to ask. You can look at the paper I cited. 

As to your second point, the problem is that TMS does not produce
stationary noise but very short and strong current pulses. If your
system gets saturated and stays saturated for some time as a result
there is nothing you can do with flat lines by any digital means. If you
have a system that can accommodate such a pulse (24-bit EEG), this is
the second option I mentioned in my previous message. As I said, it's
possible but I haven't heard of anybody who really combined TMS with
24-bit EEG. I anyone does know such a person I'd be glad to hear about
it myself.

Best,

Vladimir  

-----Original Message-----
From: nima dehghani [mailto:nimadehghani at scientist.com] 
Sent: Friday, May 30, 2003 7:52 PM
To: Vladimir Litvak
Cc: eeglablist at sccn.ucsd.edu
Subject: RE: [Eeglablist] EEG/ERP and TMS

Dear Dr. Litvak
when i was reading your reply, a question arised in my mind!
one of the solutions that you proposed: "disconnecting the electrodes
from the amplifiers shortly before the TMS pulse and reconnecting them
as rapidly as possible after the pulse" may reduce the noises during the
intervals; but in the other hand, "EXACTLY" at the time of reconnection,
it may induce a great disturbance in the system which could possibly
last for "fashionable" amount of time!...
what is your idea?and did you experienced it yourself? and is not it
better to record in a steady noisy environment than having no noise at
some moments PLUS great disturbances at other times? steady noises, at
least, may give us chance for postprocessing filtering more easily!
cheers
nima dehghani 
Babak Imaging Center

----- Original Message -----
From: "Vladimir Litvak" <litvak at alice.nc.huji.ac.il>
Date: Fri, 30 May 2003 08:29:22 +0200 
To: "'Jim Kroger'" <jimkk at umich.edu>, <eeglablist at sccn.ucsd.edu>
Subject: RE: [Eeglablist] EEG/ERP and TMS

Re: Only the first paper mentioned by Arno (Komssi et al.) is relevant
for
Re: what you were asking. The second one does not involve EEG
recordings. 
Re: 
Re: I have some personal experience with combining TMS and EEG and I
also
Re: heard what other people are doing. Indeed, there are TMS artifacts
that
Re: can saturate the EEG amplifiers for periods ranging from 20 ms to a
few
Re: seconds (depending on the kind of the amplifier and the electrode
Re: position). In general there are two possible strategies for dealing
with
Re: them. One approach is building a cut-off circuit that will
disconnect
Re: the electrodes from the amplifiers shortly before the TMS pulse and
Re: reconnect them as rapidly as possible after the pulse. The drawback
of
Re: this solution is that the reconnection will necessarily take time
during
Re: which there will be no recording at all. The group at the Helsinki
Re: University Hospital where the technique was developed published a
number
Re: of studies based on it. Check out http://www.biomag.helsinki.fi/
and
Re: also http://www.nexstim.com /
Re: The latter link is I think the only company that sells a complete
Re: TMS/EEG setup. There are also a number of people who built their own
Re: setups based on similar principles: Alvaro Pascual-Leone in Boston,
Re: Vincent Walsh in London and Walter Paulus in Goettingen. Perhaps
there
Re: are others as well. The scheme of the circuit is available in the
Re: literature: 
Re: 
Re: Virtanen J, Ruohonen J, Naatanen R, Ilmoniemi RJ (1999)
Instrumentation
Re: for the measurement of electric brain responses to transcranial
magnetic
Re: stimulation. Med Biol Eng Comput 37:322-326.
Re: 
Re: Another approach is using an EEG system with a high dynamic range
that
Re: will not be saturated by TMS artifacts. This approach has not been
Re: applied yet for TMS as far as I know but it is being developed to
Re: perform EEG recordings inside an fMRI device. In this case there
will be
Re: large artifacts in the recordings but the recording system will not
Re: saturate, no data will be lost, and it might therefore be possible
to
Re: remove artifacts by digital processing. I think EEG systems that can
be
Re: used inside the fMRI scanner will become increasingly widespread and
Re: most of them will probably be good for TMS as well.
Re: 
Re: Best,
Re: 
Re: Vladimir Litvak
Re: Evoked Potentials Lab
Re: Technion - Israel Institute of Technology  
Re: 
Re: 
Re: -----Original Message-----
Re: From: eeglablist-admin at sccn.ucsd.edu
Re: [mailto:eeglablist-admin at sccn.ucsd.edu] On Behalf Of Jim Kroger
Re: Sent: Thursday, May 29, 2003 10:48 PM
Re: To: eeglablist at sccn.ucsd.edu
Re: Subject: [Eeglablist] EEG/ERP and TMS
Re: 
Re: I'm hearing some mention of using TMS with EEG/ERP. I presume the
TMS 
Re: pulse will make collection of EEG data impossilbe for some period.
Re: 
Re: Has anybody experience with various data collection systems and TMS?

Re: Are some better than others for this purpose? Any pointers to
further 
Re: information?
Re: 
Re: Thanks
Re: Jim
Re: 
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web:
http://www.iranmedical.com/HomePage/index.cfm?parampage=practice&id=nima
dehghani
email:
nimadehghani at scientist.com, nimadehghani at iranmedical.com

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