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Did you explicitly compare the two groups in your whole brain analysis, and show that one group is greater than the other? Or did you do two separate (one-sample) tests and show that one group activates and the other doesn't. If you did the first, than an ROI analysis should show the same thing. If you did the second, then an ROI analysis might show no difference, because there might not be a significant difference, especially if the group that shows activation is only marginally significant. The second group could be just subthreshold, or could have a larger variance, leading them to not be significantly activated, but also not different from the active group. -Mike -- Mike Angstadt Research Computer Specialist / PANLab Lab Manager Department of Psychiatry / University of Michigan (734) 936-8229 > -----Original Message----- > From: SPM (Statistical Parametric Mapping) [mailto:[log in to unmask]] > On Behalf Of MRI Study > Sent: Thursday, July 03, 2014 10:58 AM > To: [log in to unmask] > Subject: [SPM] Whole brain vs ROI: different results > > Dear spm-list, > > I have conducted preliminary whole brain analyses in a pre-test - post-test > design for two groups. The other group shows activation changes between > the sessions in a certain brain region, the other one doesn't. However, when > I conduct an ROI analysis for this region, I find a very similar activation change > between the two groups; that is, it doesn't seem that the other group shows > a change in activation between the two sessions of a greater magnitude than > the other group. What could be the reason for this? I have run the ROI > analysis with both mean and peak activation, but both look the same. > > Thanks for and ideas and help! ********************************************************** Electronic Mail is not secure, may not be read every day, and should not be used for urgent or sensitive issues