# Coherence!

Muthuraman Muthuraman muthuraman10 at HOTMAIL.COM
Tue Jan 9 11:08:41 CET 2007

```Hello ,

I am using the DICS method in source analysis

The data i have is 64 electrode EEG data in which there are 4 EMG channels
So my aim is to have a refrence to be one of the EMG electrodes with respect
to all the EEG channels
and find the source area in respect to the refrenced EMG channel

A basic question, i do not have any anatomical MRI data is it useful to do
the source analysis
without it, in future i will have the MRI data

So the first step of calculating the coherence using the freqanalysis
and these are the steps i follow

emgindx = strmatch('M', hdr.label);
rstindx = setdiff(1:length(hdr.label),emgindx);

trl = [];
trl(:,1) = [21:1000:172040-1000]';
trl(:,2) = [1020:1000:172040]';
trl(:,3) = 0;

cfg         = [];
cfg.dataset = 'pd_mof_tr0_o_0307.cnt';
cfg.trl     = trl;
cfg.channel = hdr.label(rstindx);
cfg.implicitref='M1';
cfg.reref   = 'all';
cfg.blc     = 'yes';
data        = preprocessing(cfg);

cfg.channel  = hdr.label(emgindx);
cfg.hpfilter = 'yes';
cfg.hpfreq   = 10;
cfg.rectify  = 'yes';
emg          = preprocessing(cfg);

for j = 1:length(emg.trial)
emg.trial{j} = blc(emg.trial{j});
end
data         = appenddata([],data,emg);

%MTMFFT

cfg            = [];
cfg.method     = 'mtmfft';
cfg.output     = 'powandcsd';
cfg.channel    = channelselection({'all' 'M1'}, data.label);
cfg.channelcmb = channelcombination({'all' 'M1'}, data.label);
cfg.foilim     = [2 30];
cfg.taper      = 'hanning';
cfg.keeptrials = 'yes';
cfg.variance   = 'yes';
cfg.jackknife  = 'yes';
freqmtmfft     = freqanalysis(cfg, data);
fdmtmfft       = freqdescriptives([], freqmtmfft);

%MTMWELCH

cfg            = [];
cfg.method     = 'mtmwelch';
cfg.output     = 'powandcsd';
cfg.channel    = channelselection({'all' 'M1'}, data.label);
cfg.channelcmb = channelcombination({'all' 'M1'}, data.label);
cfg.foi        = [2:2:30];
cfg.t_ftimwin  = ones(1,length(cfg.foi)).*0.5;
cfg.taper      = 'hanning';
cfg.keeptrials = 'yes';
cfg.variance   = 'yes';
cfg.jackknife  = 'yes';
freqmtmwelch   = freqanalysis(cfg, data);
fdmtmwelch     = freqdescriptives([], freqmtmwelch);

I have attached a figure with this mail[Coherence between C3 and M1] in
which there is a difference in coherence values
for the fieldtrip method and the welch periodogram method with and without
laplacian transform

Is there any input parameters i can change in the fieldtrip analysis
so that i can have the similar values, or is there any major differences in
the methods
with fieldtrip and Welch periodogram method.

thanking you

with regards
M.Muthuraman

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