first steps using lcmv

Nathan Weisz weisz at LYON.INSERM.FR
Fri Mar 2 18:40:12 CET 2007


Hi everyone,

in order to explore the usage of the lcmv option of sourceanalysis
i'm using eeg data (35 electrodes)  with an auditory N1. topography
is attached. within fieldtrip i did a dipolefit, and the output looks
relatively sensible (perhaps a little deep and posterior, but overall
not bad for EEG :-)). however when i run lcmv sourceanalysis,
plotting the "neural activation index" gives me something really
terrible (also attached). since the "solution" appears relatively
clear in this case, i guess i have done something stupid at some point.

the steps:

dat=eeglab2fieldtrip(EEG,'preprocessing');

cfg=[];
cfg.latency=[.09 .12]; %latency of my N1
cfg.covariance='yes';
cfg.keeptrials='yes';
datTest=timelockanalysis(cfg,dat);

vol = [];
vol.r = [0.88 0.92 1.00]*85;
vol.c = [1 1/80 1];       % conductivity
vol.o = [0 0 0];

cfg=[];
cfg.vol=vol;
cfg.grid.xgrid='auto';
cfg.grid.ygrid='auto';
cfg.grid.zgrid='auto';
[grid] = prepare_leadfield(cfg, datTest); %the same LF-matrix used
for 'good' dipole fit

cfg=[];
cfg.grid=source2sparse(grid);
cfg.method='lcmv';
cfg.vol=vol;
cfg.projectnoise='yes';
[sourceN1] = sourceanalysis(cfg, datTest);

cfg=[];
cfg.powmethod='none'; %only option that works
[sourcenai] = sourcedescriptives(cfg, sourceN1);

cfg =[];
cfg.funparameter  = 'nai';
sourceN1F=source2full(sourcenai);
[interp]=sourceinterpolate(cfg,sourceN1F,mri);
sliceinterp(cfg,interp)


I'd really appreciate pointers of what I may be doing wrong.

thanks a lot,
nathan

ps: as for the mri, i'm using the mri in MRI4Fieldtrip with
coordinates transformed to conform my headmodel coordinates.



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