REM : Sorry if you already recieved this mail, but as it had the same object
field than the response maid by Christian I thought that you may have missed
it.
Dear Christian, and others
Thank you very much for your comments (and thanks for the reference, it is a
huge month for SEM in practice).
Let me just rephrase some part of the preceding mail, so you'll just have to
say where I'm wrong.
>
>
> > Could you help me in specifying the definition of effective connectivity
> > and in its evaluation by PPI & SEM ?
> > Would EFFICIENT connectivity under a cognitive constrain be a good
> > approximation of this idea (something that is more easy to translate in
> > french) ?
>
> I am not sure why you think that the term effective connectivity should be
> rephrased into efficient connectivity.
If I did well understood, the classical formulation of 'effective
connectivity', stated that a neuron A was considered e-connected (for
effectively connected) with the neuron B depending on the probability for the B
neuron to spike if the A neuron did (the higher it is, the more A is
e-connected with B), thus the idea that efficiency could be a good synonym. I
haven't heard about modulatory influences to be considered as e-connection, and
many thanks for any correction or reference that would invalid this view.
However, this is what PPI is looking for : modulation, with a double possible
explanation :
1 - change in EC from area A to B due to the psychological factor,
2 - modulation of the activation raised by the psychological factor by the area
A input
3 - (may be a third possibility were both are acting and modulating each other)
(Sorry for rewriting what you have already written 3 years ago in your PPI
article, but it is just for clarity ;-)
This is why I was asking you whether EC (effective connectivity) should be
reserve for area that respond to 2 contrasts : the interaction, and the
covariation with the influencing area (A) = possibility 1? If true, shouldn't
we mask the PPI result with the 'functional connectivity' result (covariation
with area A) ?
In the same way, should the modulatory connection (MC) = possibility 2, only be
raised when the PPI activated area is also activated by the psychological
factor (and again mask by it) ?
At last, wouldn't the last possibility be raised when both factor in isolation
do play a role in the PPI activated area (and then double masking the
interaction contrast with the two first) ?
Sure, a last possibility remain : that only the interaction term is
statistically significant. I suppose that in this case the interaction is
negative and is crossing around zero. And I cannot see how to decide from 1,2
or 3 (any idea is welcome).
To summarize, some basic questions remain (living aside the undecided case) :
Is EC = efficient connectivity (case 1) + MC (modulatory connectivity)
[although it seems acceptable to me, I am not sure that MC case was considered
in the electrophysiological definition using JPSTH, but again please correct me
if I'm wrong]
Or is EC = efficient connectivity , and in this case would be part of the
functional connectivity essemble.
At last, since the region used as regressor is supposed to be related to a
factor orthogonal to the used contrast, how to be sure that the interaction
term does not simply reflect the interaction between the two factors (unless it
has been computed, and thus all report of PPI should include the report of this
computation as negative) ? In a way, the third area problem (area C that is
connected to A and B and explain why they are correlated), could be viewed as
replaced by an other confounding factor.
????????????? thanks for your lights ??????????????
I hope to be able to listen to your talk in Paris on the 23rd of May
Thanks for your authoritative advises
Sincerely
Jack
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