[FieldTrip] EEG source reconstruction with template - elec file

[Silvia Formica]

Dear all,


I have a EEG dataset, collected with a Biosemi system with 64 channels. I don't have the individual anatomical data for each participant, but I want to perform source reconstruction to have at least a rough localization of the activation I find.


Therefore, I intend to use the templates provided by fieldtrip. If I understand correctly, independently of the source modelling technique that I will choose to use, I need the following information:


1) the head model : this would be the template 'standard_bem'


2) the source model : the template 'cortex_5124.surf.gii'


3) the elec information :? this file should describe the spatial configuration of the electrodes, but I can't retrieve it. I don't think any of the templates available fits my data (they all have more than 64 channels and different configurations).


I tried to use the function ft_read_sens on my data but I get the following error


elec    = ft_read_sens([data_filt5.mat'],'senstype','eeg');


Undefined function or variable 'lab'.

Error in channelposition (line 316)
n   = size(lab,2);

Error in ft_datatype_sens (line 349)
        [chanpos, chanori, lab] = channelposition(sens);

Error in ft_datatype_sens (line 158)
    sens = ft_datatype_sens(sens, 'version', '2011v2');

Error in ft_read_sens (line 380)
sens = ft_datatype_sens(sens);



I found the cartesian coordinates of the electrodes on the Biosemi website, with the x y z coordinates for each electrodes (as the little example I'm giving below, but that's not enough.


Channel             x                                        y                                        z
Fp1                 -27.0333934563814 83.2002299946862 -3.05493522574547
AF7                 -51.4205700085246 70.7743429000555 -3.05493522574547
AF3                 -35.5608995849164 76.2605952593987 24.1279774030766
F1                     -25.1195714566887 62.1731210759014 56.2665567427342
F5                     -47.7073482911603 58.9136687505812 43.7676114900325

...                   ?    ...                                        ...                                    ...



Do you have any suggestions on how to create a correct elec file fitting my data?

Any help would be highly appreciated!


Silvia



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