[Eeglablist] Methodological question on connectivity

[Ryan McGinn]

Hi Marco,

There is no reason why you would not be able to use Granger causality in
this case.  Granger causality is not strictly an event-dependent measure.
 Nevertheless, the brain state may not be transient even though the
external manipulations (in this case hypnosis) may be.

The temporal window for granger causality (or the order of the analysis - a
measure of what amount of signal is used in prediction) is a difficult
thing to set, in general.  There are a number of information criteria (such
as the aikake information criterion) that may help, but there is no
definitive answer here, as far as I am aware.  What you are essentially
asking is what is the memory of the system - i.e. what amount of time
previous to a given event is necessary to predict it?

As to whether granger causality is correct, it is likely not correct;
however, it may give some useful information.  The standard Granger causal
measure is linear and as such does not strictly apply to highly nonlinear
systems such as the brain.  It is also not defined in the frequency domain,
as are some newer methods such as partial directed coherence.  Since the
brain appears to rely on frequency, this may be a poor assumption.
 Granger's original paper is a good one, and worth the read.

Ryan

On Wed, May 2, 2012 at 8:08 AM, Marco Rotonda <marco.rotonda at gmail.com>wrote:

> Hi all,
> I have some methodological questions on connectivity and I would like
> to share you my doubts in the hope to solve them.
>
> I would like to ask you if I could apply Granger Causality or other
> connectivity analysis to a non transient event.
> I mean I would like to know if it is possible to analyse an hypnosis
> induction.
> In this case I have not many events to check but only one long session
> where I could take 2-3 minutes in between.
> I would like to analyze at the beginning, during the induction and
> after the induction what's going on.
>
> So now my questions are:
> - is it correct to think using GC in this case?
> - is it correct to take these 3 moments during the induction and treat
> them as 3 different conditions?
> - if yes, how long should be the ideal temporal window (in classical
> FFT analysis is 4 seconds)
>
>
> Thanks in advance
>
> Marco
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