[FieldTrip] Dimension of lead-field Matrix

pooneh baniasad pooneh.baniasad at gmail.com
Mon Oct 3 13:01:37 CEST 2016


Dear Simon,

I've followed this tutorial:
http://www.fieldtriptoolbox.org/tutorial/headmodel_eeg_bem to construct the
headmodel ('VolBEM')
I use 'standard_1020.elc' for 'elec' and 'cortex_20484.surf.gii' for
'DipPos'.
Is it clear or should I explain more? ūüôā

On Mon, Oct 3, 2016 at 11:53 AM, Simon Homolle <s.homolle at donders.ru.nl>
wrote:

> Dear pooh,
>
> Could you provide more information how you constructed your BEM-model?
>
> best regards,
>
> Simon Homölle
> PhD Candidate
> Donders Institute for Brain, Cognition and Behaviour
> Centre for Cognitive Neuroimaging
> Radboud University Nijmegen
> Phone: +31-(0)24-36-65059
>
> On 02 Oct 2016, at 12:22, pooneh baniasad <pooneh.baniasad at gmail.com>
> wrote:
>
> Dear FieldTrip community
>
> I'm using the forward model to simulating EEG signal although it seems the
> dimension of the lead-field matrix is not correct. Here is a review of the
> procedure.
>
> First I constructed a BEM headmodel for EEG source analysis ‚Äčand then by
> loading the template cortex, I put the dipoles with specific current source
> on that. I expect the dimension of the lead-field matrix will be m*n which
> m=electrode's number and n=3*dipole's number but 'm' is different.
> Since I used the template electrode 'standard_1020.elc', m = 97 according
> to:
>
>   chanpos: [97x3 double]
>     chantype: {97x1 cell}
>     chanunit: {97x1 cell}
>      elecpos: [97x3 double]
>        label: {97x1 cell}
>         type: 'eeg1010'
>         unit: 'mm'
>
> while the dimension of lead-field matrix is:  2000x122880
>
> I use this function for calculating lead-field matrix:
>
> LF = ft_compute_leadfield(DipPos, elec, VolBEM);
> ‚ÄčI do not understand why the number of raws are different‚Äč!
>
> ‚ÄčOn the other hand I guess that there is a similarity between the number
> of raws in the volume head model and LF matrix due to the dimension of
> headmodel matrix is: 2000x8000 double .‚Äč
>
> ‚ÄčI will be so thankful if anyone can help me.‚Äč
>
> --
> Bests
>
> Pouneh Baniasad
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> fieldtrip at donders.ru.nl
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>
>
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-- 
Bests

Pouneh Baniasad
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