Hi all, thanks for the comments! The idea to smooth the data was based on others papers which did not use HCP data though. I always thought that smoothing is a "good idea" for group studies in order to account for the between-subject variability in the ROI based on the different brain sizes and shapes.
The analysis I want to run uses the data from ROIs to calculate connectivity between ROIs (DCM). The ROI extraction in SPM uses the component that explains the most variance in a PCA. The extraction runs on the smoothed volumes. The ROIs are based on some probabilistic atlas (e.g. anatomy toolbox). I have about 300 subjects. I thought the results will be relatively robust for different levels of smoothing. But this is not the case. Since the CSF and WM signals have been regressed out, I did not assume that this will have influence. The unsmoothed results look much better though. greetings David 2018-05-30 0:51 GMT+02:00 Timothy Coalson <tsc...@mst.edu>: > Volumetric smoothing in particular is not advised, as it causes signal > from one bank of a sulcus to bleed into the opposite bank. Analyses that > average all signal within an ROI should have no benefits (and will have > detriments) from smoothing, as the within-ROI averaging itself is a form of > smoothing (but with a well-chosen ROI, it won't bring in signal from the > opposite sulcal bank, etc, in theory). Is this the kind of ROI analysis > you are doing? If so, I wouldn't trust the differences caused by adding > volume-based smoothing, because they could be from nearby areas instead. > > Tim > > > On Tue, May 29, 2018 at 4:24 PM, David Hofmann <davidhofma...@gmail.com> > wrote: > >> Dear all, >> >> as far as I read in previous posts on the list, spatial smoothing of the >> volumetric resting state data is not recommended. But this was with >> regard to group ICA. >> Would you also recommend not to apply any further spatial smoothing for >> the (volumetric) resting state data, when running ROI-based (group) >> analysis on multiple subjects? >> >> Comparing the results of smoothed (4,6, FWHM) and unsmoothed data gives >> highly different results in my case, so I'm a bit confused now. >> >> greetings >> >> David >> >> _______________________________________________ >> HCP-Users mailing list >> HCP-Users@humanconnectome.org >> http://lists.humanconnectome.org/mailman/listinfo/hcp-users >> > > _______________________________________________ HCP-Users mailing list HCP-Users@humanconnectome.org http://lists.humanconnectome.org/mailman/listinfo/hcp-users
