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Marco 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 memory). > 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. Darren > > Can anyone suggest a more direct way to approach this issue? > > Thank you and all the best, > Marco > > -- > 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] > > ----------------------------------------------------------------------------------- > SOSTIENI ANCHE TU LA RICERCA DEL SAN RAFFAELE. > NON C'E' CURA SENZA RICERCA. > Per donazioni: ccp 42437681 intestato a Fondazione Arete' Onlus del San > Raffaele. > Per informazioni: tel. 02.2643.4461 - www.sanraffaele.org > -- Darren Gitelman, MD Northwestern University 710 N. Lake Shore Dr., 1122 Chicago, IL 60611 Ph: (312) 908-8614 Fax: (312) 908-5073