[FieldTrip] head- and sourcemodel templates

Schoffelen, J.M. (Jan Mathijs) jan.schoffelen at donders.ru.nl
Thu Sep 13 12:11:29 CEST 2018

Hi Annika,

The template sourcemodels have been downloaded from SPM, and are based on the colin 27 MRI template.

It could be that the standard_BEM has been derived from the same image, but I am not sure. Yet, even if they have been derived from the same image, the different image processing streams and softwares used might have resulted in the meshes intersecting.

When I look at the inner boundary in conjunction with the sourcemodel, both objects are well-registered, I can confirm that the cortex sticks out a little bit in left temporal cortex, but for the rest it looks very OK to me.

I am pretty sure that FieldTrip checks whether dipole position are located outside the inner compartment of the volume conductor model (and sets them to ‘outside’ when computing the inverse solution), so the affected vertices will not affect the MNE.

Creating a consistent set of volume conduction models, with corresponding template source models is not a super straightforward process. If you happen to have such templates (or have created them) we’d be happy to hear about it.

Best wishes,

> On 7 Sep 2018, at 12:50, Annika Thierfelder <athierfelder at tuebingen.mpg.de> wrote:
> Dear fieldtrippers,
> I have a short question about the template files provided by fieldtrip. I am doing MNE source reconstruction with the template BEM headmodel and the cortical sheets provided in the sourcemodel templates. However, I noticed that the sourcemodel is outside of the BEM brain surface at some points. So I plotted it against the MRI template and it doesn't really seem to fit. It seems quite small and shifted, so it's hard to judge the shape.
> Are those not produced from the same template MRI? And would it therefore make sense to go through the process of producing a sourcemodel from the standard MRI myself as described here [http://www.fieldtriptoolbox.org/tutorial/sourcemodel#construction_of_a_source_model_based_on_a_surface_description_of_the_cortical_sheet] ?
> Thanks in advance for your advice,
> Best,
> Annika
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