[FieldTrip] help with dipole position and orientation

Frederic Roux f.roux at bcbl.eu
Wed Oct 17 15:17:24 CEST 2012

Dear list members,

I am working on CTF based MEG data and would like to run
a dipole simulation with two dipoles in the occipital cortex.
However, I am not sure how to chose
the right parameters regarding dipole position and moment.

So the first question I have is how to chose the coordinates for
the dipole position.

cfg.dip.pos = [x y z]

In a paper by Osipova et al. (2008) I read that the position can
be chosen based on the sensor array of a CTF system with respect
to head coordinates.
In this paper the dipole position was chose to be r = [-5 0 1] which
should correspond to a dipole close to the hemispheric midline and
in the occipital cortex.

Can anyone tell me based on which data / how these coordinates were
chosen? I have been searching the grad structure of my data
for comparable info, but did not find anything. Neither did I looking
at cfg.layout.pos.

My second question concerns the dipole moment.
Am I right in assuming the following:

cfg.dip.mom = [1 0 0] % dipole points towards NAS
cfg.dip.mpm = [-1 0 0] % dipole points away from NAS

cfg.dip.mom = [0 1 0] % dipole points towards LPA
cfg.dip.mom = [0 -1 0]% dipole points towards RPA

cfg.dip.mom = [0 0 1]% dipole points towards vertex
cfg.dip.mon = [0 0 -1]% dipole points away from vertex

Any help or suggestions would be highly appreciated.


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