[Eeglablist] Is dipfit ever used for purposes other than localising source space data?

[Makoto Miyakoshi]

Dear Arno,

> We have never claimed that ICA components localize to point like regions
(the flux of current in a small patch of cortex can be well represented
with a point like dipole at a slightly deeper location

SCCN has been claiming what I call 'small patch hypothesis' for the
ICA-resolved cortical effective source. For example, see Delorme et al.
(2012).

...There are strong biological reasons to believe that under favorable
circumstances ICA should separate signals arising from local field
activities in physically distinct, compact cortical source areas: First,
short-range (<100 micrometer) lateral connections between cortical neurons
are vastly more dense than longer-range connections [3,4]...

The extremity of this view is SCALE algorithm by Akalin-Acar and Makeig
where patch size serves as a cost function to be minimized by changing
skull conductivity as independent variable.

According to Nunez and Srinivasan (2006), cortical patch size should be > 1
inch^2 to be detected at the scalp sensor. See my talk on
https://youtu.be/lRyZxt2WeKk?t=1392 Also Nunez and Srinivasan (2006) Fig.
1-20.

Makoto



On Fri, Jul 12, 2019 at 9:12 PM Arnaud Delorme <arno at ucsd.edu> wrote:

> > Let me tell you dirty secret of dipfit.
> > In order for cortical activation to be recorded at the scalp level
> without
> > averaging, the patch size should be > 1 inch^2 (Nunez and Srinivasan,
> > 2006). However, dipole model assumes a spatial point with 6 parameters.
> > Therefore, estimating dipolar sources of scalp-recorded potential means
> to
> > model spatially spread cortical patch with a point. This is a fundamental
> > violation of the dipole model.
>
> The dipole model is a mathematical tool that works well to
> summarize/compress data (6 values; 3 position; 2 moment; 1 amplitude) can
> often explain scalp topographies with 256 channels with 99% accuracy which
> indicates that this is a “good” model (6 numbers explaining 256 numbers).
> We have never claimed that ICA components localize to point like regions
> (the flux of current in a small patch of cortex can be well represented
> with a point like dipole at a slightly deeper location - I believe it is
> mathematically equivalent but would welcome validation from a source
> localization expert).
>
> If you do not like dipoles, in Dipfit 3 you can also use eLoreta to
> calculate distributed source models associated with ICA components.
>
> Best wishes,
>
> Arno
>
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-- 
Makoto Miyakoshi
Assistant Project Scientist, Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego