if (FALSE) {
   fsbrain::download_optional_data();
  # Define the data to use:
  subjects_dir = fsbrain::get_optional_data_filepath("subjects_dir");
  subject_id = 'subject1';
  surface = 'white';
  hemi = 'both';
  atlas = 'aparc';
  region = 'bankssts';
  # Create a mask from a region of an annotation:
  lh_annot = subject.annot(subjects_dir, subject_id, 'lh', atlas);
  rh_annot = subject.annot(subjects_dir, subject_id, 'rh', atlas);
  lh_label = label.from.annotdata(lh_annot, region);
  rh_label = label.from.annotdata(rh_annot, region);
  lh_mask = mask.from.labeldata.for.hemi(lh_label, length(lh_annot$vertices));
  rh_mask = mask.from.labeldata.for.hemi(rh_label, length(rh_annot$vertices));
  # Edit the mask: add the vertices from another region to it:
  region2 = 'medialorbitofrontal';
  lh_label2 = label.from.annotdata(lh_annot, region2);
  rh_label2 = label.from.annotdata(rh_annot, region2);
  lh_mask2 = mask.from.labeldata.for.hemi(lh_label2, length(lh_annot$vertices),
   existing_mask = lh_mask);
  rh_mask2 = mask.from.labeldata.for.hemi(rh_label2, length(rh_annot$vertices),
   existing_mask = rh_mask);
  # Visualize the mask:
  vis.mask.on.subject(subjects_dir, subject_id, lh_mask2, rh_mask2);
}
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