[Eeglablist] Why most of good 'brain' ICs are 'dipolar' with show 'red'-centerd scalp topos, although 2/3 of the cortex is in sulci?

[Евгений Машеров]

Thank you. I would like to clarify his methodology. Perhaps it is described in detail somewhere? It seems to me that the frequency at which the impedance is measured may be significant here.

Eugen Masherov

> Yes, this electrical stimulation approach was attempted by Don Tucker's EGI
> group for many years - with results that were not encouraging, the problem
> being that almost all the injected current flows through the scalp, whose
> local and time-varying conductivity also then has significant effect... The
> SCALE approach treats the independent component signals compatible with an
> effective source in cortex (having a strongly dipolar scalp projection with
> equivalent dipole located in brain) as cortical stimulations, and
> iteratively finds the (single) skull conductivity value that
> minimizes reconstruction error of the brain sources to 'sparse, compact,
> and smoothly' varying distribution (sometime, two bilaterally
> near-symmetric distributions) on the imaged cortical surface - using an
> electrical forward problem head model constructed from an individual MR
> image - the SCS source inversion algorithm of Cao Cheng. Our next step
> should be to build a multidimensional skull conductivity map. Again, we are
> attempting to put the SCALE software on NSG (https://urldefense.com/v3/__http://www.nsgportal.org__;!!Mih3wA!BNS_5aZCEDYflkuo2qfpDZgsY0Z-xv87AU3QM1QiNdQklstxqDvGifU6oaUANNcbLSF18LJVuTtkYo2KIrZI$ ) for free
> use.
> 
> Scott Makeig
>