[Eeglablist] Dipole localization and ICA

[Makoto Miyakoshi]

Dear Iman,

> 1-      As far as I know, EEGLAB uses ICA components for source localization
> and they claim that each ICA component corresponds to a (or a pair of)
> dipole?

Yes.

> So, if you choose N ICA components, is  each of them fit separately
> ?

Yes.

> in other words, for source localization, does the EEGLAB algorithm
> consider all the selected components at a same time and do localization for
> all of them

Yes.

> – if the presence of one component affects of the location of
> the dipole which corresponds to the other component- ?

This never happens. ICs are constrained to be temporally maximally
independent of each other, but no constraint for spatial location.

> if yes, so, how can
> we say one dipole is associated with one ICA component?

ICA computes scalp maps. Dipole location is computed from the map
using dipfit (or equivalent).

> 2-      Is there any study on the fact that how many dipoles should be
> chosen from N-Channel EEG/MEG recording?

I'm not sure choose for what, but we usually use the residual variance
of 15% after dipole fitting to evaluate the goodness of ICs. Please
see Delorme et al. (2012) 'Independent components are dipolar' PloS
One.

Makoto



2012/11/8 Iman M.Rezazadeh <irezazadeh at ucdavis.edu>:
> Hi everyone,
>
> I have  two questions re dipole localization:
>
>
>
> 1-      As far as I know, EEGLAB uses ICA components for source localization
> and they claim that each ICA component corresponds to a (or a pair of)
> dipole? So, if you choose N ICA components, is  each of them fit separately
> ? in other words, for source localization, does the EEGLAB algorithm
> consider all the selected components at a same time and do localization for
> all of them – if the presence of one component affects of the location of
> the dipole which corresponds to the other component- ? if yes, so, how can
> we say one dipole is associated with one ICA component?
>
> 2-      Is there any study on the fact that how many dipoles should be
> chosen from N-Channel EEG/MEG recording?
>
> Best,
>
> Iman
>
>
>
> Iman M.Rezazadeh, PhD
>
> Postdoctoral Research Fellow
>
> Center for Mind and Brain
>
> University of California, Davis
>
> irezazadeh at ucdavis.edu
>
> Cell:310-490-1808
>
> Skype: Imanmr
>
>
>
>
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-- 
Makoto Miyakoshi
JSPS Postdoctral Fellow for Research Abroad
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego