Projecting sources error (individual to ICBM152)

Hello!

I have computed individual mixed head models for four subjects (cortex+aseg atlas excluding cerebellum). I did the merging according to the DBA tutorial.
I computed the sources for each subject using dSPM. Now I would like to project these sources to the default anatomy (ICBM152) for group analysis. (Project sources > Default anatomy > cortex_15002V)

The projecting was successful for two of the subjects; with the other two I got the following error:

Error using tess_interp_tess2tess (line 201)
Database error: The surface you use for the interpolation must be downsampled again.

Error in bst_project_sources (line 163)

Error in tree_callbacks>@(h,ev)bst_project_sources(ResultFiles,sDefCortex(iCort).FileName) (line 2615)

What could I have done wrong to get this error? I don't recall any differences when importing the anatomy or computing the mixed surface files and I'm trying to understand why the projecting works for only some of the subjects. The cortex files I used were all downsampled to 15002 vertices before they were merged with the deep structures.

Is there any additional information you need? Any help with this would be greatly appreciated. Thank you!
Ella-Mari

I don't know what is causing this bug. The freesurfer registered are for some reason missing from the anatomy files. However, I will not go further to debug this approach because the mixed head models are really not aimed at working at group level.
We don't have any method for projecting the sources obtained in the subject space to the template space.
I added warnings about this in the documentation, and may move one step further and disable it directly in the code.
https://neuroimage.usc.edu/brainstorm/Tutorials/CoregisterSubjects#Mixed_head_models
https://neuroimage.usc.edu/brainstorm/Tutorials/DeepAtlas

If you need a clear access to subcortical ROIs and/or if you are not satisfied with unconstrained orientations on the cortical surface, I recommend using volume source models:
https://neuroimage.usc.edu/brainstorm/Tutorials/TutVolSource
https://neuroimage.usc.edu/brainstorm/Tutorials/CoregisterSubjects#Volume_source_models

Okay, thank you very much for your help and advice!

Best regards,
Ella-Mari

Hello again!

Regarding the use of the mixed head models, I understand that they cannot be used to work at group level. I was wondering if it would be possible to calculate the sources and do individual analysis using the mixed model, and then extract only cortical sources and use these for group analysis.

There seems to be some slight differences between the sources of the cortical and mixed models (see images attached).

Kuva1 Kuva2

We only have a small group of five subjects and this issue might not be anything significant, but we were wondering if this is something possible to consider and not too big a task?
We would like to use the constrained model as it would give suitable results in relation to literature.

Thank you for your help!

You would introduce a bias between subjects. I would not recommend it.

There seems to be some slight differences between the sources of the cortical and mixed models (see images attached).

The source space is different, the maps are therefore going to be different.
Quantifying the differences between different source spaces is complicated, saying which one is better is impossible with real recordings (you need to run simulations where you know exactly the truth).

We only have a small group of five subjects and this issue might not be anything significant, but we were wondering if this is something possible to consider and not too big a task?
We would like to use the constrained model as it would give suitable results in relation to literature.

It would be simpler to run your analysis both with a fully unconstrained model (volume source model using a group grid) and with a constrained model (location + orientation constraints).
Ideally, your observations with both approaches should converge.