[Mne_analysis] Correspondence of source space with parcellation : another doubt ...

Eric Larson larson.eric.d at gmail.com
Fri Sep 6 10:00:45 EDT 2019
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> I am still stuck with the correspondence of the source space with
> parcellation.

In general, a source space takes the high resolution mesh (~100k verts) and
subselects a small subset of them (~10k or less). The subset is stored in
`src[0]['vertno']` for the left hemi and `src[1]['vertno']` for the right.

Parcellations are generally defined (by FreeSurfer) on the entire high
resolution cortical surface, and thus should contain many more points than
our decimated source space.

So, for a given source space (e.g. ico 4, 2562 sources per hemisphere) I
> would expect to find the vertices 0...2561 in the parcellation.

The parcellation can have holes. In the case of "aparc" the medial wall
vertices are missing:

>>> import surfer
>>> brain = surfer.Brain('fsaverage', 'lh', 'white', views='med')
>>> brain.add_annotation('aparc', borders=False)

[image: Screenshot from 2019-09-06 09-58-16.png]

Also keep in mind that the decimated source space vertices being numbered 0
to 2561 is a property unique to `fsaverage` (and how its spherical mesh is
arranged), in general for other subjects these can and will be integers
spanning the whole ~100k brain space.

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