[FieldTrip] One label missing after ft_virtualchannel

Marta Stojanovic martastojanovic1 at net.hr
Wed Aug 9 17:59:53 CEST 2023

Hi Fieldtrip Community, 
I'm reaching out regarding an error I previously noticed when running ft_virtualchannel. 
Namely, in my call to the ft_virtualchannel function, I used timelock data that includes trial information, a sourceanalysis output struct, and a lower resolution atlas created by interpolating the source average output from ft_sourceanalysis with the Brainnetome atlas using ft_sourceinterpolate. 
My call to the ft_virtualchannel looks like the following:
clear atlas_lowres;cfg = [];cfg.parameter = 'all';cfg.interpmethod = 'nearest';atlas_lowres = ft_sourceinterpolate(cfg,atlas,source_avg);atlas_lowres.pos = source_avg.pos;atlas_lowres.coordsys = 'mni'; % ensure mni spacedisp('Done aligning atlas to source average')
 %% parcellate single trials clear parc_trls;cfg = [];cfg.method = 'pca';cfg.parcellation = 'tissue';parc_trls = ft_virtualchannel(cfg, tlck_all, source_avg, atlas_lowres);disp('Done parcellating single trials')The atlas_lowres struct includes the following fields:
      dim: [20 25 22]
      transform: [4×4 double]
      unit: 'mm'
      tissue: [20×25×22 double]
      tissuelabel: {1×246 cell}
      cfg: [1×1 struct]
      pos: [11000×3 double]
      coordsys: 'mni'
However, after running the function, the parc_trls struct is the following, with one less label:
parc_trls = 
  struct with fields:
       trial: [144×245×1018 double]
       time: [0 0.0020 0.0039 0.0059 0.0079 0.0098 … ]
       dimord: 'rpt_chan_time'
       label: {245×1 cell}
       cfg: [1×1 struct]
       grad: [1×1 struct]
       sampleinfo: [144×2 double]
       trialinfo: [144×2 double]
       brainordinate: [1×1 struct]
When checking the label, I realise one parcel/label for the left lateral amygdala is missing.
I wonder what the missing label could pertain to. I know I can run the function with cfg.pos, which I have done previously. I curious as to why this error might arise when specifying cfg.parcellation as 'tissuelabel' and parcellating the trials based on the atlas parcel labels.
Thanks in advance,

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