# [FieldTrip] fieldtrip Digest, Vol 16, Issue 1

aida ghahremani ghahremani.aida at gmail.com
Fri Mar 2 00:56:57 CET 2012

```Dear Fieldtrip group

I have got a problem with a very simple program to solve a forward problem.
I used the below program to compute leadfield from a source in the origin
for two electrodes in different locations. I noticed that when I change the
position of one of the electrodes, it affects on the leadfield of the
other. I know it should not be like that, since electrodes do not affect

elec.pnt=[4.6*cos(pi/3) 4.6*sin(pi/3) 7.96;4.6*cos(pi/6) 4.6*sin(pi/6)
7.96];
for i=1:2
elec.label{i} = sprintf('%03d', i);
end

% create a concentric 3-sphere volume conductor, the radius is the same as
for the electrodes
vol = [];
vol.r = [8 8.1 8.6 9.2]; % radii of spheres
vol.c = [1 1 1/80 1];       % conductivity
vol.o = [0 0 0];          % center of sphere

% compute the leadfield for a dipole at position [0 0 0]
pos = [0 0 0];

% compute the potential distribution for a dipole with z-orientation
mom = [0 0 1]';
pot = lf * mom;
end

Best
Ayda

On Thu, Mar 1, 2012 at 6:00 AM, <fieldtrip-request at donders.ru.nl> wrote:

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> Today's Topics:
>
>   1. question about MNI alignment (Ali Bahramisharif)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 29 Feb 2012 21:10:54 +0100
> From: "Ali Bahramisharif" <ali at cs.ru.nl>
> To: fieldtrip at donders.ru.nl
> Subject: [FieldTrip] question about MNI alignment
> Message-ID:
>        <fac73988589583150fc4a6a7a958a215.squirrel at squirrel.science.ru.nl>
> Content-Type: text/plain;charset=iso-8859-1
>
> Dear Fieldtrip users,
>
> I want to create MNI-aligned grids in individual head-space, and I follow
> the guidelines in :
>
>
>
>
> I do not know how old this page is, but I noticed that for example in the
> current version "cfg.coordinates" should be "cfg.coordsys". I have the
> following problems:
>
> 1- When I run "ft_plot_mesh(template_grid);", I get a cubic grid which is
> apparently different from the one shown in the page.
>
> 2- When I run, ft_plot_vol(hdm), it does not seem to be aligned to
>
> I checked my segmented volumes, and they seem to be fine, and I did not
> need to run flipdim. I am wondering whether my segmented data is correct
> or it should be flipped somewhere. Please let me know if anybody knows how
> to resolve this problem.
>
> Cheers,
> Ali
>
>
>
>
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> End of fieldtrip Digest, Vol 16, Issue 1
> ****************************************
>
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