[FieldTrip] MNI grid alignment in subjects for group comparison

[Johanna Zumer]

Dear Marco,

I agree that sentence is not phrased ideally.   It is refering to the
source data structure, i.e. the output of ft_sourceanalysis.  Specifically,
copy the template_grid.pos to source.pos and then this updated source data
structure can be used in ft_sourcegrandaverage.  Likewise,it can be
overlaid on the MNI brain.   I'm not sure if the other fields are
necessary, if they are, maybe someone else can comment.

Best,
Johanna


2013/1/11 Marco Curado <marco.curado at yahoo.com.br>

> Dear Fieldtrip experts,
>
> I have a question on MNI aligned grids for subjects head prior to source
> reconstruction.
>
> In my experimental design, there are three experimental conditions (A, B
> and C) I want to compare in one group of subjects at the source level. To
> be able to compare source activity (by LCMV beamforming) among them, I use
> the MNI grid warped in every subject's head (to allow comparison at the
> source level) as stated in the tutorial "Create MNI-aligned grids in
> individual head-space":
>
>
> http://fieldtrip.fcdonders.nl/example/create_single-subject_grids_in_individual_head_space_that_are_all_aligned_in_mni_space
>
> Up to now, everything is ok. But as I am naive in beamforming, I am a bit
> confused on the last sentence of this tutorial, where it is stated:
>
> "You can use these single subjects' MNI grids in source analysis. After
> that you should put .pos, .xgrid, .ygrid, .zgrid, .dim field from the
> template_grid onto the subjects's source, which is thereby in MNI
> coordinates."
>
> My question (indeed very basic) is what is exactly referred as the
> subject's source? Is it the final source localization after LCMV? I.e., do
> I need to insert such template_grid parameters in subject's parameter as
> last step after all source localization?
> Summing up: The procedure would be to use the .grid from the subject
> (already warped with MNI grid) for source localization with LCMV and after
> it I include these parameters from the template-grid?
>
> Thanks a lot for your comprehension and attention to my question - I hope
> I was clear in my issue.
> My best wishes of an excellent year to everybody,
> Marco Curado
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