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## SPM@JISCMAIL.AC.UK

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Subject:

DCM questions

From:

Sam W.

Date:

Sun, 10 Feb 2019 07:15:55 +0000

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 ```Hi, I've just started to learn DCM and I was wondering what would be the best way to specify my model. My experimental design consists of a 2 condition x 3 valence. Condition has two levels (active and passive), and valence has three levels (positive, negative and neutral). The example in the SPM manual uses a visual input regressor consisting of every visual stimulus, but this doesn't seem to be the recommendation for factorial designs, so I'm wondering how to use the SPM design I already specified. My hypothesis is that there will be forward connectivity from region A to region B for positive emotional words only in active condition but not in passive condition. So is condition my modulatory input and all words my driving input? Or should I specify only positive words as my driving input? In the SPM design matrix I have the following regressors ActivePos, ActiveNeg, ActiveNeu, PassivePos, PassiveNeg, PassiveNeu With only two regions, and the driving input to region A, my C-matrix should look like 1 1 1 1 1 1; 0 0 0 0 0 0, correct? If active condition has a modulatory effect on connection A to B during positive words, then my B-matrix should be b(:,:,1)=[0,0;0,1] b(:,:,2:6)=[0,0;0,0] is that correct? Thank you! Sam ```