Dear SPM users and especially VBM users,
According to the script cg_vbm_optimized.m (provided by http://dbm.neuro.uni-jena.de/vbm.html), it seems that there's no smoothing after the segmentation. And since the templates using in normalization, which is created by cg_create_templated.m, have been smoothed by 8mm as default, I'm wondering whether it's needed to smooth the last image files.
Two groups with about 30 normal subjects respectively were involved. I did the analysis following the instruction of VBM tools, created my own template and use the optimized protocols. At last, I used the images with and without smoothing respectively in statistics, and got completely different results. The lateral view of four results in two studies were attached. It can be easily found that the two unsmoothed result in two studies are quite similar, with few and less significant punctate "activation" in lateral site and the posterior cerebellum of both hemisphere. When the images are smoothed, the results become much more significant (the threshold from uncorrected p0.05 to corrected p0.05), and show different patterns, (different from the unsmoothed results, and different between the two studies), with more diffused "activation" in the brain.
Do these results mean that the unsmoothed results come from some kinds of errors introduced in the previous processing, and the smoothing corrects the errors and thus the smoothed results should be the right ones?
Or actually the unsmoothed ones are correct and the additive smoothing just introduces false positive results?
Or the conflicts suggest that there's something wrong in the previous steps?
Thank you very much for your intelligence and nice help.
Best regards,
Joyce
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Joyce J.P. Yang ([log in to unmask])
State Key Lab of Brain and Cognitive Neuroscience
The University of Hong Kong
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