[FieldTrip] Generate a source model where dipoles are perpendicular to the cortex surface

["Jörn M. Horschig"]

Hi Ying,

when computing the leadfields you can set the option cfg.reducerank, 
which 'nulls' the dimension(s) which explain(s) the least variance (this 
is not quite true, but figuratively speaking). I think this is what 
comes closest to what you are looking for. There is no way to explicitly 
set desired orientations to zero apart from modifying the leadfield 
structure yourself. But that should be easily achievable, right?

Best,
Jörn

On 5/22/2014 10:26 AM, Ying Li wrote:
> Dear all,
>
> I tried to use fieldtrip to generate a source space and calculate lead 
> field matrix. I found that the dipoles in the source space has x, y, z 
> orientations. Is it possible to generate a source model where the 
> dipole is perpendicular to the cortex surface?
>
> Actually this can be very helpful, since it will reduce the unknown 
> variables and make the inverse problem easier to solve. Also, there 
> are some inverse algorithms which require the dipole to be 
> perpendicular to the cortex surface.
>
> Thanks a lot!!!
>
> Best,
>
> Ying
>
>
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-- 
Jörn M. Horschig
PhD Student
Donders Institute for Brain, Cognition and Behaviour
Centre for Cognitive Neuroimaging
Radboud University Nijmegen
Neuronal Oscillations Group
FieldTrip Development Team

P.O. Box 9101
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