[FieldTrip] Questions on Functional Connectivity results using debiased wPLI

[SERGIO OSORIO GALEANO]

Dear Fieldtrip community,

I'm estimating Functional Connectivity between 100 source-reconstructed
signals using the debiased wPLI and I have a couple of questions about my
results (code snippet below).

1) Regardless of whether I use my full time window of interest (0-1.5 s) or
whether I estimate wPLI for two separate shorter time windows (0-.7 s and
.7-1.5 s), the results are always identical to one another. Is this normal
behaviour in wPLI analyses or is there something potentially wrong with how
I've implemented it?

2) I notice that wPLI values are way lower for low-frequencies (4-7hz) than
for higher-frequencies (8-12hz and 15-30hz). While this could be a real
effect associated with my task, the fact that this result is consistent
across different conditions makes me wonder whether I've done something
wrong in the ft_freqanalysis configuration.

Thanks a lot in advance for any help anyone can provide!

-----------

cfg                 = [ ];
data               = ft_preprocessing(cfg,rwdata);

%resample data
cfg                      = [ ];
cfg.resamplefs   = 250;
data                    = ft_resampledata(cfg, data);

data =
  struct with fields:

      fsample: 250
      trial:   {1×117 cell}
      time:  {1×117 cell}
      label: {100×1 cell}
      cfg:    [1×1 struct]

% next, call the ft_freqanalysis function in our source data
cfg                     = [ ];
cfg.output          = 'fourier';
cfg.method        = 'mtmfft';
cfg.taper            = 'dpss';
cfg.foi                 = linspace(4,30,30);
cfg.tapsmofrq     = 4;
cfg.toi                 = 0:.02:1.5;   % try 0:.02:.7 and .7:.02:1.5
tf_data                = ft_freqanalysis(cfg,data);

tf_data =
  struct with fields:

            label:     {100×1 cell}
            dimord: 'rpttap_chan_freq'
            freq:       [1×30 double]
            fourierspctrm: [4563×100×30 double]
            cumsumcnt: [117×1 double]
            cumtapcnt:   [117×1 double]
            cfg:               [1×1 struct]

% estimate wPLI values
cfg                    = [ ];
cfg.method       = 'wpli_debiased';
connect_data   = ft_connectivityanalysis(cfg,tf_data);

connect_data =
  struct with fields:

               label:     {100×1 cell}
               dimord:  'chan_chan_freq'
               wpli_debiasedspctrm: [100×100×30 double]
               freq:  [1×30 double]
               cfg:   [1×1 struct]

Best,

Sergio.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20210915/50ef7f29/attachment.htm>