Deep source modeling (phase 1)

[payamsash]

Reference issue (if any)

First phase of #14097, also see #6784

What does this implement/fix?

adds setup_subcortical_source_space which should/will support both label (aseg) and surface (e.g coming from CBM).

Additional information

This is just a Proof-of-concept with sample subject.

[payamsash]

you can test it with this small code snippet:

import mne
from mne.datasets import sample

subjects_dir = sample.data_path() / "subjects"
subject = "sample"

# label
src_label = mne.setup_subcortical_source_space(
    subject, label=["Left-Hippocampus", "Left-Amygdala"], subjects_dir=subjects_dir
)
print(src_label.kind)

# surface (e.g for CBM)
surface = subjects_dir / subject / "surf" / "lh.white"
src_surface = mne.setup_subcortical_source_space(
    subject, surface=surface, subjects_dir=subjects_dir, keep_largest_component=False
)
print(src_surface.kind)

# cortex + subcortical
cortex_src = mne.setup_source_space(
    subject, spacing="oct4", add_dist=False, subjects_dir=subjects_dir, verbose=False
)
mixed = mne.SourceSpaces(list(cortex_src) + list(src_label))
print(mixed.kind)

# quick plot 
brain = mne.viz.Brain(
    subject,
    subjects_dir=subjects_dir,
    hemi="lh",
    surf="white",
    alpha=0.3,
    background="white",
    cortex="low_contrast",
)
brain.add_volume_labels(labels=["Left-Hippocampus", "Left-Amygdala"])

[ttaiv]

Thank you @payamsash! I ran you test code snippet using a cerebellar surface for sample from CMB and it worked well. I created a source space with cerebellum and cortex with mixed = src_surface + cortex_src and was able to plot it with mixed.plot().

[drammock]

additions to the FIFF standard need to go in https://github.com/mne-tools/fiff-constants. Presumably this would go here-ish:

https://github.com/mne-tools/fiff-constants/blob/9ccb09d69daa8332f2e7252638ba397b60ba2502/DictionaryTypes_MNE.txt#L89-L95

[payamsash]

Done, see this PR. I also added a temp one here: mne/_fiff/tests/test_constants.py