[Eeglablist] Meaning of ITC

Thu Apr 16 02:00:18 PDT 2009

Dear Makoto Miyakoshi:

 I have read you post at the EEGLab forum and maybe I am completely wrong
but ITC in at least in the way is computed in the EEGLab can be related with
ERPS and has to analyze with muh caution. ITC has been or phase consitency
has been propose as one of the possible mechanism to generate the ERPs. If
for example you have a singal in the single trial which phase are random
except at lets say 30ms in wich ideally all the phase have the same value,
then when you perform the average you will see a nice ERPs come up. The only
problem here  is that in the case that you have an increase in power or an
ERPS you could have a similar behaviuor but just because a fix latency and
amplitude component will produce the exactly the same behaviour. Thus why
you have to be very carefull when applying and interprete the ITC results
because you can confound effects and maybe the effect you are looking is
just related with an increase in the EEG signal over the single trial or an
ERP in this case ITC will have the same interpretation (because it could be
generater) like the ERP. I will advice you to paper in this file that I
think are really illustrative of this problem and can give some ligth on
this issue:

STATISTICS IN MEDICINE
Statist. Med. 2008; 27:2922–2947
Published online 13 December 2007 in Wiley InterScience
(www.interscience.wiley.com) DOI: 10.1002/sim.3132
Exploring event-related brain dynamics with tests on complex
valued time–frequency representations.
by Eduardo Martinez-Montes et.al

and

Detection of synchronized oscillations in the
electroencephalogram: An evaluation of methods
Psychophysiology, 41 (2004), 822–832. Blackwell Publishing Inc. Printed in
the USA.
Copyright r 2004 Society for Psychophysiological Research
DOI: 10.1111/j.1469-8986.2004.00239.x
by NICK YEUNG et. al

I will before trying to find any possible explanation I will rule out that
something like the one describe in this paper are not happening and then you
can really try to find the reason for the ITC. If you have a mix situation
like the one this paper describe it will be very difficult to do it.

Have a nice day and sorry if this note does not answer your question or you
already knew about this issue
Ernesto Palmero Soler

2009/4/16 Makoto Miyakoshi <mataothefifth at yahoo.co.jp>

> Dear Pal,
>
> >From this reply I hope our communication is normally logged on the
> eeglablist.
>
> Yes, the Bereitshcafts Potentials seems a good example, if the potential
> were constructed by phase locking (I'm not sure on this point). By the way,
> could you specify 'Alan Gevins works from around 1984' which I could not
> find? I want to take a look at the illustrations.
>
> The immediate meaning of ITC is 'trial-by-trial EEG phase coherency at a
> certain IC/scalp channel, time bin, and frequency range, is likely to be
> this much'. It only reflects (at least in princiele) the timing of neural
> firing (large portion of neurons), and does not reflect the amount of it
> (though ERSP and BOLD do, in constrast, in my understanding). Certainly, a
> physiological meaning of ITC is a event-related 'timing' of neuronal
> firing.
>
> So, my question again may be: what is the 'psychological' meaning of ITC
> increase/decrease, given that it does not reflect increase/decrease of
> involved neuronal activity? Maybe I'm too much used to a simple schema that
> associates ERSP/BOLD increase with 'activation' of a certain portion of
> neurons.
>
> Makoto
>
>
>
>
>
>
>
> --- P $B>-%% (Bl Gunnar Larsson <Pal.Gunnar.Larsson at epilepsy.no> wrote:
>
> > Dear Makoto
> >
> > > Dear Pal,
> > >
> > > Thank you for the reply. It is very informative and interesting...
> > > almost exciting.
> > >
> > > It seems to me, however, that the term 'synchronization' is used in
> > > different meanings between you and me. Maybe you mean it in a sense
> > of
> > > 'synchronized firing among neurons at a given moment', right? There
> > are
> > > actually papers that report inter-channel coherency, and that is
> > > certainly a kind of synchronization. But the concept of ITC is
> > 'inter-
> > > trial'
> > > synchrony: it compares EEG phases AMONG TRIALS and measure phase
> > > variance, so it had nothing to do with inter-channel phase
> > synchrony.
> >
> > You do have a point. I don't know your research at all. Is inter
> > trial between stimuli or between sessions or between persons? I have
> > not thought this through, but I was thinking between stimuli and
> > something not unlike to bereitschaft-potentials, but mainly my pont
> > was on the relation betwen bold and EEG.
> >
> > >
> > > Maybe we'd better create a term 'Inter-neuronal coherency (INC)' in
> > > contrast with inter-trial coherency (ITC).
> > Coherency in EEG was very popular, but it did not lead to very much
> > more than some papers. One of hte main reasons was that spatial
> > filters were not applied (except by Gevins) and hence there were too
> > much blurring of the findings. I guess you should look at Alan Gevins
> > works from around 1984. He did 128 channel EEG and made arrows
> > showing coherences and latencies between brain areas. His
> > illustrations have been widely used in the literature. To my
> > knowledge he did not look at ITC.
> > >
> > > I'm analyzing my EEG data and found some experimental effect in
> > ITC,
> > > but I have no idea how to interpret it... because theoretically it
> > is
> > > not related to neither ERSP (EEG power) nor BOLD.
> > Back to bereitschaft - there is no expectance in this?
> > >
> > > I will ask EEGLABlist technicians how to post our communications to
> > the
> > > list. By the way, so far you are the only person who replied. My
> > > gratitude is all yours (haha).
> > >
> >
> > Regards
> >
> > P $B%;%e<+ (Bl
> >
> > > Makoto
> > >
> > >
> > >
> > > --- P $B<@</<'<' (Bl Gunnar Larsson <Pal.Gunnar.Larsson at epilepsy.no>
> wrote:
> > >
> > > > Dear Makoto
> > > >
> > > > First - I thought it went back to the list, but did not check to
> > see
> > > > that it did.
> > > >
> > > > My points was mostly towards the Nunez take on this;
> > synchronization
> > > > does not require energy. Hence synchrony comes out with high EEG-
> > > power
> > > > and no BOLD-effect. On the other hand, interneurons in cortex are
> > so
> > > > symmetrical that they do not show up on EEG, but consumes quite a
> > bit
> > > > of energy and will be well seen in fMRI.
> > > >
> > > > According to the above, your phase locking(?) would be expected
> > to
> > > > influence EEG-power but not BOLD (or ?).
> > > >
> > > > Another point from Nunez: If you have a million stochastic firing
> > > > neurons, they would give a resultant amplitude of A*sqrt(n) where
> > A
> > > is
> > > > the amplitude and n is number of neurons. However, when they are
> > > > synchronized, the amplitude is n*A. So a million neurons will
> > show
> > > > same amplitude as 1000 synchronized neurons! This gives that
> > small
> > > > systems may dominate the EEG you record.
> > > >
> > > > P $B<'<=<'t@<- (Bl
> > > >
> > > > -----Opprinnelig melding-----
> > > > Fra: Makoto Miyakoshi [mailto:mataothefifth at yahoo.co.jp]
> > > > Sendt: 14. april 2009 03:54
> > > > Til: P $B<'<=<'t@<- (Bl Gunnar Larsson
> > > > Emne: RE: [Eeglablist] Meaning of ITC
> > > >
> > > > Dear Pal,
> > > >
> > > > Thank you for your fast response and information.
> > > > Neurovascular coupling is the essential phenomenon with BOLD and
> > it
> > > > has totally different time constant than EEG... that is fine with
> > me.
> > > > That said, what I'm wondering is the meaning of ITC. On the one
> > hand,
> > > > ERSP is a measure of EEG power, which most likely reflects sum of
> > > > regional neuronal activities, which should be associated with
> > BOLD
> > > via
> > > > neurovascular coupling (in principle). On the other hand, ITC has
> > > > nothing to do with EEG power, since it is a measure of
> > inter-trial
> > > > phase variance, therefore it should not affect BOLD either. Then,
> > > what
> > > > is the meaning of ITC in contrast with ERSP/BOLD?
> > > >
> > > > By the way, your response does not seem to be sent to EEGLAB
> > list.
> > > > Why don't we re-send it to the list?
> > > >
> > > > Makoto
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > --- P $B<><B<><1<><)<><) (Bl Gunnar Larsson
> <Pal.Gunnar.Larsson at epilepsy.no>
> > wrote:
> > > >
> > > > > I think you should read the paper by PL Nunez on the relation
> > > > between
> > > > > EEG and fMRI from 2000 (or 1999?). EEG and BOLD is very
> > different
> > > > > entities. Also, the EEG- parameters are direct functional
> > measures
> > > > > which gives responsen from a few miliseconds to some seconds
> > > > > (Pfurtscheller). BOLD on the other hand, is the change in
> > > > oxygenation
> > > > > due to change in bloodflow due to change in energy consumption
> > due
> > > > > change in activity. Hence the effect is very indirect and shows
> > a
> > > > > maximum after some 5s. E.G. AM Dale et al has shown some nice
> > use
> > > > of
> > > > > the BOLD and EEG/MEG so there no reason to discard one, just
> > use
> > > > with
> > > > > care.
> > > > >
> > > > > P $B<><)<><?<><)<#<(<></ (Bl
> > > > >
> > > > > -----Opprinnelig melding-----
> > > > > Fra: eeglablist-bounces at sccn.ucsd.edu
> > > > > [mailto:eeglablist-bounces at sccn.ucsd.edu] P $B<><)<><?<><)<#<(<></
> (B
> vegne av
> > > Makoto
> > > > > Miyakoshi
> > > > > Sendt: 10. april 2009 11:25
> > > > > Til: eeglablist at sccn.ucsd.edu
> > > > > Emne: [Eeglablist] Meaning of ITC
> > > > >
> > > > > Dear experts,
> > > > >
> > > > > Let me take a question about a basic physiology.
> > > > > In my intuition, ERSP (i.e. EEG power) is related to neuronal
> > > > > activation, either firing frequency or number of firing cells.
> > On
> > > > the
> > > > > other hand, ITC (i.e. inter-trial EEG phase) is NOT directly
> > > > related
> > > > > to them. So, by observing ITC, we may be observing some already
> > > > > systematized temporal responsibility of the given network,
> > which is
> > > >
> > > > > too complicated and abstract to imagine, compared to the case
> > of
> > > > > neuronal firing simply increasing/decreasing.  Does it mean,
> > then,
> > > > ITC
> > > > > is a totally different index than, for example, BOLD?
> > > > >
> > > > > Makoto
> > > > > _______________________________________________
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> > > >
> > > >
> >
> >
>
>
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