[Eeglablist] Meaning of ITC

Fri Apr 17 06:34:45 PDT 2009

> 
> Dear Baris,
> 
> Thank you for your response. I agree with you. As you mentioned, ITC
> must be related to the 'optimal point which maximizes the neural
> operation' in a certain way. In my poor understanding of neural
> physiology, punctuality of neuronal firing should derive from the fact
> that each neuron has a specifically optimized 'time limit' to accept
> pulses from other neurons, and only pulses arrived within the limit are
> summed to decide whether to fire. In principle, temporal regulation of
> a macroscopic electrophysiological phenomenon such as EEG still must be
> explained by the prerequisite... that's my guess. Any comment?

First very brief to your question. An action potential the jumps to a postsynaptic neuron , will change its membrane potential. The cell will reset the potentila relative fast. If the synaps is far from the cell body ithas little influence and will soon be "forgotten" as a synaps close to the cell body that will have much more "powewr" over a longer time. To that there is a significant dynamic in location and matabolism of reseptors which would be expected to change the system. To that input to the system will change the state of the system. Input may be sensory, chemical, activity from other parts of the brain and so on, so yes, there are lots of static and dynamic prerequisits in the system. Also, signals you put on to the system will probably make changes to it.

Here is a small program you can look at: If you add 100000 action potentials to a time segment, you get something that look like white noise, if there is no driving in the system. You may try this:

for i=1:100000
punkt=floor(rand(1,1)*987)+1;
eeg_data(punkt:punkt+11)=eeg_data(punkt:punkt+11)+action';
end

Where action is: action=[0 -1 -2 0 2 4 2 0 -1 -3 -1 0]

If you continue with in the same variable

for i=1:10000
punkt=floor(rand(1,1)*20)+500;
eeg_data(punkt:punkt+11)=eeg_data(punkt:punkt+11)+action';
end

That is 10000 now and it may only vary over a small segment of the time line (20 points).

Now you see that the 10000 constrained "action potentials" totally dominates the 100000 unconstrained.

So to conclude, anything that influences the probability of the firing rate will influence the signal in a larger degree than one would initially believe and there are lots of factors changing the probability. The firing rate per se is not that important.

Regards

Pål

> 
> About task modulation on ITC, you can find it on any of Makeig's
> papers.
> 
> Makoto
> 
> 
> 
> 
> 
> 
> 
> 
> 
> --- Sukru Baris Demiral <demiral.007 at googlemail.com> wrote:
> 
> > Or, the other way of asking this question is why the neural system
> > needs inter trial coherence. Is it a random effect, or is the
> > inter-trial-coherence time an optimal point which maximizes the
> neural
> > operation.
> > How does the variation and timing of Trial Coherence change with the
> > task demands?
> >
> > BAris
> >
> > 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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> > --
> > SB Demiral, PhD.
> > Department of Psychology
> > 7 George Square
> > The University of Edinburgh
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