Dear Christian,
Thanks to you and to Geraint for those precisions.
You mentioned Volterra-kernels which still look like a kind of mathematical
monster to me.
As far as I remember, the only paper mentioning it was the Karl's MRM
paper, and I haven't found many help in the mail archives. Is there other
reference on this, or could you comment briefly on its basis, and the way
to use it in SPM99b. I feel like missing something important here.
Many thanks to all of you for all this time spent for answering.
Best regards
Jack
-----Message d'origine-----
De: Christian Buechel [SMTP:[log in to unmask]]
Date: mercredi 22 septembre 1999 12:32
A: [log in to unmask]
Cc: Geraint Rees; Foucher Jack
Objet: Re: About psychophysiological interaction
Dear Jack,
> |5- The way I figure it could only be name functional connectivity, not
> |effective, since no model is imposed. True ? Thus to do effective connec
> |tivity, one should plot the intensity of one voxel against the one of
> |another that have to be specified (another activated regions for
example).
>
> I would defer to others on the subject of effective connectivity. My
> understanding is that by imposing a model, an analysis of effective
> connectivity allows an estimation of the relative contribution of
multiple
> other ROIs to evoked activity in a voxel of interest. In the analyses
> discussed here, only the contribution of a single physiological source of
> activity (in ROI X) is considered.
Geraint is absolutely right. However you could think about a design
matrix in which the time-series of multiple voxels is used. This would
then allow the contribution of multiple areas on certain target areas
and therefore enter the area of effective connectivity. If you would
further consider non-linear effects (and temporal memory) amongst those
areas this would conceptually lead to the idea of Volterra-kernels.
-Christian
--
Dr. C. Buechel
Research Fellow
Functional Imaging Laboratory
Wellcome Dept. of Cognitive Neurology
12 Queen Square
WC1N 3BG London
UK
Tel.: +44-171-833-7483
Fax.: +44-171-813-1420
email: [log in to unmask]
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