[Eeglablist] Question regarding color interpretation

Frank Duffy fhd at sover.net
Sun Sep 20 12:49:47 PDT 2015

The image provided was created artificially in the BESA dipole 
simulation program which I believe may be downloaded from the BESA.de 
website if you would like to pursue your own dipole simulations.

The "source dipole" is shown by a red dot with a line. A dipole is like 
a small battery with positive and negative ends. The line represents the 
positive end and the line also shows the source orientation/direction. 
As different ends project to different hemispheres, the hemispheres show 
different polarities (red positive, blue negative). As the source is 
placed near the midline, source voltage projects to both hemispheres. 
Source projections are also shown as waveforms upon the scalp to the 
right. Note that the display polarity is positive up, unlike standard 
EEG which shows negative up.

Most sources are near cortex with greatest amplitude over the nearby 
scalp. Projected activity to the other hemisphere is low amplitude, 
usually hidden by other activity in that hemisphere BUT sources always 
project in opposing directions, one end positive and one end negative.


Frank H. Duffy, MD
fhd at sover.net
> Dr. philos. Pål G. Larsson
> Seksjonsleder Klinisk nevrofysiologi
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> *Fra:*eeglablist-bounces at sccn.ucsd.edu 
> [mailto:eeglablist-bounces at sccn.ucsd.edu] *På vegne av* Fang-Yu Chang
> *Sendt:* 14. september 2015 14:28
> *Til:* eeglablist at sccn.ucsd.edu
> *Emne:* [Eeglablist] Question regarding color interpretation
> Dear EEGLAB users,
> I have a question regarding the scalp map color bar. I have read the 
> following webpage:
> http://sccn.ucsd.edu/pipermail/eeglablist/2003/000030.html
> Based on my understanding, red and blue both indicate activation, but 
> opposite polarity. My question is, if there's an event that results in 
> one side of the brain having red readings while the other side has 
> blue readings, how would this data be interpreted?
> Sincerely,
> Stella Ling
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