[FieldTrip] Fitting dipole to a topography: objective function is undefined at initial point

Ksenia Volkova voxxys at gmail.com
Tue Sep 1 12:54:33 CEST 2015

Dear fieldtrip users,

I have encountered a problem getting dipole fit to a topography observed on
consecutive time points. I have attempted to format the data appropriately
(Tzvetan, thank you for your help!), but the call to ft_dipolefitting function
returns the "Objective function is undefined at initial point" error both
during gridsearch and nonlinear search. What could be the cause of such
behavior? Could it be that electrode coordinates are somehow in a wrong
format (I have taken mine from an eeglab dataset) or would they anyway be
projected onto head surface and cause wrong results, but not an error?

Thank you in advance for any help.

Ksenia Volkova

Dear Ksenia,
> I would first start with the organization of the data in a format
> FieldTrip can sense.
> data = [];
> data.trial ={[chan x time]} % this is your elec x topography matrix, where
> topography is observed on consecutive time points
> data.time = [vector-number of time points];
> data.label = {?elec1?,?elec2? etc.} your electrode labels
> data.elec = this is key reflecting the position of the electrodes relative
> to the head
> Next, you have to compute a volume conduction model. How to do so is
> explained here:
> http://www.fieldtriptoolbox.org/tutorial/headmodel_eeg?s[]=eeg&s[]=volume&s[]=conduction&s[]=model
> After this you can proceed with the dipole fitting which is explained for
> instance here:
> http://www.fieldtriptoolbox.org/tutorial/natmeg/dipolefitting#fit_a_dipole_model_to_the_meg_data
> Under cfg.latency you could specify the number of the topography you are
> interested in and under cfg.vol the BEM model you computed in the previous
> step. If you don#t have individual MRI
> you can use the standard BEM model located in the
> ~template/headmodel/standard_bem.mat. Note that before you do so you
> should coregister the headmodel with the electrodes using
> ft_electroderealign.
> Good luck
> tzvetan
> > Dear fieldtrip users,
> >
> > I wonder if you can help me out. I have a relatively simple problem:
> having a topography matrix (where rows correspond to topographies, and
> columns correspond to channels) I want to fit a dipole to each topography.
> I have looked through tutorials and documentation and I've seen this
> example
> http://www.fieldtriptoolbox.org/example/compute_forward_simulated_data_and_apply_a_dipole_fit.
> Still, I can't figure out how I should use the toolbox to solve my problem.
> >
> > What would be the right arguments to call ft_dipolefitting with in my
> case? If I have EEG data, topography matrix and channel locations, what
> would be the easiest way to fit a dipole to each topography?
> >
> > Thank you in advance for any help.
> >
> > Ksenia Volkova
> > _______________________________________________
> > fieldtrip mailing list
> > fieldtrip at donders.ru.nl
> > http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
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