[FieldTrip] problem with surface Laplacian

Hwee Ling Lee hweeling.lee at gmail.com
Wed Dec 17 11:45:09 CET 2014

Dear all,

I have 60 channel EEG resting state data, and after discarding bad
channels, I am left with 48 channels common to all subjects.

I applied scalp current density to my data before extracting power
information from my EEG data. The EEG cap that I used was in a 10-10
system, and I don't have the electrode position file. Hence, I used the
default electrode position file named 'standard_1005.elc' for the purpose.

Here's the part of my script for the surface Laplacian:

    cfg_neighb.method = 'template';
    cfg_neighb.layout = 'EEG1010.lay';
    cfg_neighb.channel = 'all';
    cfg_neighb.feedback = 'no';

    neighbours = ft_prepare_neighbours(cfg_neighb, data7);

    cfg                 = [];
    cfg.method          = 'finite';
    cfg.elecfile        = 'standard_1005.elc';
    cfg.elec            = ft_read_sens(cfg.elecfile);
    cfg.trials          = 'all';
    cfg.neighbours      = neighbours;
    cfg.conductivity    = 0.33;

    data8               = ft_scalpcurrentdensity(cfg, data7);

When I tried to extract power from data8 (after surface Laplacian), I keep
getting an error message (see below). I'm not sure why this would be the
case, and would appreciate very much if someone could help me resolve the

Thank you!

Here's my script for extracting the power:
 cfg                 = [];
    cfg.output          = 'pow';
    cfg.channel         = {'all'};
    cfg.method          = 'mtmfft';
    cfg.keeptrials      = 'no';
    cfg.tapsmofrq       = 5;
    cfg.layout          = 'EEG1010.lay';

    % for frequencies up to 30 Hz
    cfg.foilim          = [1 30]; % either the full range of frequencies
(data2.hdr.Fs/2) or up to 100 Hz
    cfg.taper           = 'hanning';

    % find the index for the c200 condition
    pre_c200_idx = find(data8.trialinfo == 200);
    cfg.trials          = pre_c200_idx;
    LF_pre_c200        = ft_freqanalysis(cfg, data8);

Here's the output plus error message:

the input is raw data with 48 channels and 343 trials
Error using ft_datatype_sens (line 375)
inconsistent number of channels in sensor description

Error in ft_datatype_raw (line 138)
      data.elec = ft_datatype_sens(data.elec);

Error in ft_checkdata (line 223)
  data = ft_datatype_raw(data, 'hassampleinfo', hassampleinfo);

Error in ft_freqanalysis (line 209)
data = ft_checkdata(data, 'datatype', {'raw', 'raw+comp', 'mvar'},
cfg.feedback, 'hassampleinfo', 'yes');

Best regards,
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