[Eeglablist] Dipoles and Volume Conduction

[Tyler Grummett]

Hey ahmed,

I could be wrong, but doesn't it say in the literature that the N100 represents attentional resources from the frontal lobes (most likely the ACC). So that would be a good result, wouldn't it?

Tyler


On 4 Dec 2014, at 8:04 am, Ahmed Almurshedi <ahmed19875000 at yahoo.com<mailto:ahmed19875000 at yahoo.com>> wrote:

Dear Experts,

I have noticed in some ERP experiments that the response is flipped in the posterior part than anterior part of scalp. For example in checkerboard pattern VEP, P100 response on mid occipital electrode and N100 response on the frontal electrode.
According to the discussion with colleagues they said that ERP response are usually from the generation of a dipole, the field of which is picked up at different electrode locations.  Thus, some will pick up the positive end, and others will pick up the negative end. This is often called phase reversal, as the phase of waveform is 180 degrees reversed.

My question is, why the dipoles distribution is symmetric over the scalp? According to my understanding there is an infinite number of dipoles may contribute in a specific source.  Is there any justification (Please correct me if I'm wrong)?

Also why the volume conduction effect (transmission of electric current from primary source electrode to other electrodes) can be seen in some experiments only while it's much less in some other experiment? What's the experimental factors may effect on volume conduction?

Thank you,

AHMED



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