[FieldTrip] EEG source reconstruction with template - elec file

[Julian Keil]

Dear Silvia,

how is the electrode location information from the BioSemi website not
enough?
Basically, you can create your own electrode definition by giving the
labels and locations to a structure, e.g.
elec.label{1} = 'Fp1';
elec.chanpos(1,:) = [-27.0333934563814, 83.2002299946862,
-3.05493522574547];

or for all your electrodes in one go:
elec.label = {'Fp1','AF7','AF3','F1','F5'};
elec.chanpos = [-27.0333934563814, 83.2002299946862, -3.05493522574547;...
-51.4205700085246, 70.7743429000555, -3.05493522574547;...
-35.5608995849164, 76.2605952593987, 24.1279774030766;...
-25.1195714566887, 62.1731210759014, 56.2665567427342;...
-47.7073482911603, 58.9136687505812, 43.7676114900325];

plot3(elec.chanpos(:,1),elec.chanpos(:,2),elec.chanpos(:,3),'*')

or of course read them more elegantly from a text file ;-)

It might be a good idea to double check the alignment with the template
headmodel afterwards using ft_electroderealign
You can then use this elec structure in all subsequent analyses.

I hope that helps,

Julian

On Thu, Jan 10, 2019 at 10:59 AM Silvia Formica <Silvia.Formica at ugent.be>
wrote:

> 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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> https://mailman.science.ru.nl/mailman/listinfo/fieldtrip
> https://doi.org/10.1371/journal.pcbi.1002202
>
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