On Thu, Feb 10, 2011 at 5:07 AM, marco tettamanti
<[log in to unmask]> wrote:
> Dear all,
> I don't think that this question has been addressed before:
> I would like to set up a DCM analysis with fMRI data to investigate the
> following issue: we have identified an activation in a very well known
> network of 4 brain regions (A,B,C,D), and we believe that, in our task, this
> network can be gated - depending on which one of 2 different input
> modalities is involved - by the activity of two other distinct networks,
> each including 3 brain regions (E,F,G, or H,I,J).
> That is, we would like to assess how network EFG interacts with network ABCD
> in modality 1 and how network HIJ interacts with network ABDC in modality 2,
> in the context of a sort of 2x2 (Modality x network-network interaction)
> factorial design.
> I presume that one could address this, by simply treating each brain region
> independently, and for instance by using BMS to test whether the preferred
> model fits the expected interaction patterns, but I think that there may be
> problems with the relatively large number of regions (>8).
You can deal with this by setting up the DCM file from the command
line. If you set up a simpler DCM using the GUI you will see what
fields you need. The 8 region limitation is mostly due to the gui (and
> I also presume that the question could be approached by non-linear DCM, even
> though I think that non-linear DCM has been only used in the context of the
> influence of one single region on a system of interconnected regions, and
> not in the context of network-network interactions.
I'm not sure how you could use a non-linear DCM in this scenario. You
can't really setup a small DCM network as an input, per se. The two
"subnetworks" would just be connected into the larger 4 region network
perhaps through a common area. This would be through an intrinsic
connection. DCM only accepts as inputs the condition-type vectors that
it extracts from an SPM.mat file. You would also need other actual
inputs into each of the subnetworks in order to drive overall system
activity. Non-linear DCM's can be used to modulate an intrinsic
connection, so perhaps you are thinking of using the 3 region
subnetworks to modulate an external input into the 4 region network?
However, I don't think you can modulate an input as DCM is currently
set up, and you would still need to drive the subnetworks in some way.
> Can anyone suggest a more direct way to approach this issue?
> Thank you and all the best,
> Marco Tettamanti, Ph.D.
> San Raffaele Scientific Institute
> Via Olgettina 58
> I-20132 Milano, Italy
> Tel. ++39-02-26434888
> Fax ++39-02-26434892
> Email: [log in to unmask]
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