Indeed that is one of the major fallacies in brain imaging. Have a look at this paper in press at PNAS:
https://www.biorxiv.org/content/early/2018/04/23/255620 Peace, Matt. From: David Hofmann <[email protected]<mailto:[email protected]>> Date: Wednesday, May 30, 2018 at 5:14 AM To: Timothy Coalson <[email protected]<mailto:[email protected]>>, Matt Glasser <[email protected]<mailto:[email protected]>> Cc: hcp-users <[email protected]<mailto:[email protected]>> Subject: Re: [HCP-Users] Additional smoothing of FIX extended resting state data? 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 <[email protected]<mailto:[email protected]>>: 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 <[email protected]<mailto:[email protected]>> 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 [email protected]<mailto:[email protected]> http://lists.humanconnectome.org/mailman/listinfo/hcp-users _______________________________________________ HCP-Users mailing list [email protected] http://lists.humanconnectome.org/mailman/listinfo/hcp-users
