# [FieldTrip] Inter-trial coherence/PLF in source space

Olga Sysoeva olga.v.sysoeva at gmail.com
Wed Nov 11 13:14:13 CET 2015

```Dear filedtripper,

But now I am back to active analysis and stucked...
I'd like to calculate ITC/PLF in a source space similar to described

- T. Bardouille
<http://www.sciencedirect.com/science/article/pii/S1053811908004989#>, ,B.
Ross, 2008 paper.
<http://www.sciencedirect.com/science/article/pii/S1053811908004989#>

I have 40Hz-auditory steady state response from 306 neuromag system. I
figured out how to calculate ITC on sensor space from complex FFT
coeficients obtained by ft_freqanalysis.

As a next step I need to do this in source space. My vision that I can use
complex FFT coeficients, obtained in sensor space but  "project" them to
source space by multiplying with weigted matrix. In the above mentioned
paper they applied the LCMV beamformer to determine the weighting function,
*w**jm*, that estimates the source activity across the steady-state time
interval in the frequency band of interest. How can I do this?

I tried to do it using ft_sourceanalysis but get lost. If I specified lcmv
method and feed it with average timelocked data as in the example

cfg = [];

cfg.method = 'lcmv';
cfg.grid = grid;

cfg.vol = test_vol;

cfg.lcmv.keepfilter = 'yes';

sourceAll = ft_sourceanalysis(cfg, test_data_LEar_avg);

or  for a frequency decomposed data using disc

cfg = [];

cfg.method = 'dics';

cfg.frequency = 40;

cfg.grid = grid;

cfg.vol = test_vol;

cfg.dics.projectnoise = 'yes';

cfg.dics.lambda = '5%';

cfg.dics.keepfilter = 'yes';

cfg.dics.realfilter = 'yes';

sourceAll = ft_sourceanalysis(cfg, test_freq_LEar);

As output I get in the sourceAll.avg.filter some weigth matrix (although I
am not fully sure if that is what I need). Unfortunately, I did not find
the way (filtrip function) to apply this filter/weigths to itc or complex
FFT coeficients. Should I write my our code for this? Which way is better:
multiply it to itc or first to complex fft and than calculate itc? Which
matrix to use (from disc or lcmv)? Is my way of thinking makes sense or am
I completely lost?

I would be really thankfull for any help.

Best Regards,
Olga Sysoeva, PhD,
Senior Researcher,
MEG-center, Moscow.
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