[Eeglablist] Dipole localization and ICA

[Makoto Miyakoshi]

Dear Iman,

> On the other hand, how could one say that the dipole which is the outcome of
DIPFIT has physiological meaning considering the fact that ICA maps are only
mathematical plots of a 'mapping matrix' .

The theoretical background in using equivalent current dipoles must be
found in Electric Fields of the Brain by Nunez though I'm not familiar
with this topic.

> In other word , how can we find
> physiological meaning of each component by saying that each ICA reflects
> individual and SEPARATE brain process - which is in my point of view far
> from reality of physiology of the brain?

I know what you mean. I also wondered whether or not the assumption of
ICA is too strong. However, empirical evidence shows that ICA on EEG
has been working well (see the history that starts from Makeig, 1996
to Delorme et al., 2012). Probably it depends on scale of measures.
fMRI studies have been successful probably for the same reason
(imagine there were no regional BOLD differences... ) Anyway, if you
want to know more about the rational of the use of ICA on EEG, I
recommend you refer to Makeig and Onton ERP Features and EEG Dynamics:
An ICA Perspective in S. Luck & E. Kappenman (2009). Oxford Handbook
of Event-Related Potential Components. New York, Oxford University
Press.

Makoto


2012/11/14 Iman M.Rezazadeh <irezazadeh at ucdavis.edu>:
> Dear Makoto,
> Thanks for your reply!
>  I think dipole approach might be  'good' for more or less localized sources
> (maps) not distributed brain area.
> On the other hand, how could one say that the dipole which is the outcome of
> DIPFIT has physiological meaning considering the fact that ICA maps are only
> mathematical plots of a 'mapping matrix' . In other word , how can we find
> physiological meaning of each component by saying that each ICA reflects
> individual and SEPARATE brain process - which is in my point of view far
> from reality of physiology of the brain?
> 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
>
>
>
>
> -----Original Message-----
> From: Makoto Miyakoshi [mailto:mmiyakoshi at ucsd.edu]
> Sent: Wednesday, November 14, 2012 4:08 PM
> To: Iman M.Rezazadeh
> Cc: eeglablist at sccn.ucsd.edu
> Subject: Re: [Eeglablist] Dipole localization and ICA
>
> 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



-- 
Makoto Miyakoshi
JSPS Postdoctral Fellow for Research Abroad
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego