Dear SPM experts,
Greetings!
Thank you for reading this. I have performed spDCM specification (using Specify Group from Batch Editor) and estimation (using DCM estimation from Batch Editor). I have several questions when using spDCM (DCM Version 12.5). Could you please help me with it?
My purpose is to compare three different groups and found the difference: whether these groups share a similar network structure and have different effective connections, neural fluctuations, and vascular reactions.
1. "Specify Group" needs two DCM templates, one is full DCM and the other is Alternative DCM. If I don't have any reduced model or nested model, could I just leave it the same as the Full DCM? Or if I have to indicate an alternative DCM, what is a good way to create one?
2. After Specify Group+ DCM estimation, does it means the DCM.mat in each subjects folder (DCM_m0001.mat?) have already been estimated and been reduced if I chose the Full+BMR estimation type?
3. I'm not sure what should I do next. Could I just use "Specify/Estimate PEB" (by selecting DCM_m0001.mat of every subject) and then using "Compare/Average PEB models" to compare these averaged models? Could I use the "Covariates" in the "Specify/Estimate PEB" to indicate different groups and then directly run "Compare/Average PEB models". What is the right way to create the Design Matrix? And how could I rectify the multiple comparisons among the three groups?
4. Besides, I'm a little confused with the output of DCM_m0001.mat. I found that (I'm not sure if I was right.) Ep.A means the endogenous coupling (ie, the effective connectivity?). Ep.a means the neuronal parameters. And Ep.transit means the transition time. However, why there is only one value in the Ep.decay, I thought it should have the same number of values as the ROIs I choose (one for each?). Where could I found it? And what do Ep.b and Ep.c stand for?
Thank you very much for your help!
Best Wishes,
Pujun Guan
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