[Mne_analysis] map between sources and voxels

[Gustavo Sudre]

Hello all,

Thank you again for the good discussing on that previous issue. Now I  
have a more MNE-specific question.

Suppose I run compute_mne_raw_inverse using a single label (e.g.  
cortex-lh.label), and then convert the output of that function to  
a .mat file using mne_raw2mat. In the resulting .mat file I see a  
[channels] by [time] matrix with data, which makes sense. Judging by  
the number of channels, I imagine they map to the sources within that  
label, and not the vertices. Then, in the info structure there are  
names for all these channels, and if I understand it correctly that  
contains the number of the vertex that the source maps to. In that  
case, is there a 1-1 relationship between sources and vertices? That  
would mean that there's an awful lot of quiet voxels in the results  
(e.g. given the ~3000 sources I get in the left hemisphere, using 7mm  
spacing, and 160K vertices being indexed). Shouldn't a given source  
affect more than one vertex in the brain, if the triangles are small  
enough?

I guess my question boils down to the definition and relationship  
between vertices and sources. Please let me know if I'm mistaken in my  
line of thought.

Thanks,

Gus