El 07/02/13, Douglas N Greve <greve@nmr.mgh.harvard.edu> escribió:

On 02/06/2013 12:49 PM, Gabriel Gonzalez Escamilla wrote:
> Dear Doug and FreeSurfer experts,
>
> Thnak you so much for all your lasts responses!.
>
> I did ran succesfully all the pre-processing for the interhemispheric
> comparisons on FS. Now I have a couple questions:
>
> given the command for interhemispheric comparisons:
> mri_glmfit --y lh.lh-rh.thickness.sm05.mgh --glmdir
> glm.lh.lh-rh.thickness.sm05 --osgm --surf fsaverage_sym lh;
>
> A) This read all subjects to construct X and C as one-sample group
> mean, this means that as result I get the difference across
> hemispheres and across my subjects in a population, right?
Correct.
>
> B) But, what if I have two groups? controls and patients, I'm
> wondering if is it possible to examine regional differences of
> thickness asymmetries between those two groups? or more?
This just becomes a standard two group analysis as described in the
tutorials. You create an FSGD file with two classes and list your input
subjects.
>
> C) If I want to examine effects of group or sex, while controlling for
> age and other factors how do I introduce them into the glm model? If
> so, do I set the contrasts as normally for mri_glmfit? I mean as any
> other thickness study? or there is any other thing that I should do?
You do not need to do anything different than with a normal thickness
study.
>
> The command for multiple comparisons correction is:
> mri_glmfit-sim --glmdir glm.lh.lh-rh.thickness.sm05 --cwpvalthresh .5
> Which performs only cluster-wise corrections,
>
> D) is there any other way to correct for multiple comparisons,
> something like permutation tests or anything else?
Yes, you can run something like
mri_glmfit-sim --glmdir glm.lh.lh-rh.thickness.sm05 --cwpvalthresh .5
--sim perm 10000 2 csdperm --sim-sign abs
You should run mri_glmfit-sim --help to see what these options mean as
you may need to change the voxelwise threshold (the "2" value)

doug
>
>
> Many thanks in advanced,
> Gabriel

--
Douglas N. Greve, Ph.D.
MGH-NMR Center
greve@nmr.mgh.harvard.edu
Phone Number: 617-724-2358
Fax: 617-726-7422

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