Dear SPM-list,
we performed a fMRI-experiment involving pain stimuli of 4 different concentrations (35, 50, 65 and 80) applied under 3 different conditions with each condition measured at baseline and post-treamtent thus resulting in 6 different conditions.
We want to test whether the concentration-dependent activation changed depended on the condition.
Is ist correct to define a -3 -1 1 3 contrast to test a concentration-dependent effect for each session? and would it be necessary to test the reverse contrast (3 1 -1 -3) and subtract it from the first contrast? Is it possible to do this on first level?
Thank you very much for your help!!
Carmen
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