[FieldTrip] across-subject analysis of source space data in a 2D triangulated cortical mesh

[Brian Maniscalco]

Hi all,

I have been doing MNE source space analysis of single-subject MEG data,
closely following the steps described here:

http://www.fieldtriptoolbox.org/tutorial/minimumnormestimate

This pipeline yields source activations distributed across a 2D
triangulated cortical mesh, as extracted from individual subject anatomical
MRI via FreeSurfer. So in order to perform across-subject analyses, it is
necessary to somehow normalize individual subject meshes into a
standardized space.

In principle it is possible to interpolate the 2D source data onto the
subject's 3D anatomical MRI and then normalize this 3D source space data
into a standardized anatomical template. However, the logic of
interpolating 2D surface activations across an entire 3D volume seems
questionable, and my initial attempts at doing just this have yielded
results that look either nonsensical or not nearly as sharp and intuitive
as the original 2D source visualization.

My question is: is there a reasonable way to normalize source space data
computed on individual subject 2D meshes onto a standardized 2D mesh,
rather than a standardized 3D volume? If there is no pre-existing template
for such a 2D mesh, perhaps a makeshift one could be computed by averaging
the geometries of the meshes of the individual subjects in this dataset?

Or to pose the question more generally, what is the best way to conduct
across-subject analysis on source space data given the kind of 2D mesh data
produced by the processing pipeline for the MNE tutorial linked above?

thanks,
Brian
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