[Eeglablist] Plotting scalp electrodes/topography neatly inside head outline

Makoto Miyakoshi mmiyakoshi at ucsd.edu
Thu Jan 9 12:32:02 PST 2014


Dear Pete,

In my experience, multiplying 0.7893 to polar radius worked (that does not
mean I correct it all the time; I don't care :-). Try this code and compare
topomaps. Don't forget to apply 'optimize center' before doing it (this
button is on the right top of channel edit window).

%%%%%%%%%%%
    for n=1:length(EEG.chanlocs)
        EEG.chanlocs(1,n).radius = EEG.chanlocs(1,n).radius*0.7893
    end
%%%%%%%%%%%

There was a big discussion in SCCN what the head 'circle' in the topoplot
should represent... generally speaking, any channels located lower than the
circumference that connects Nz-eye-earholes/auriculars-Iz should show
outside the circle (i.e. 'skirt'). Note that this 'interpretation' stands
on the assumption that the circle = Nz-eye-earholes/auriculars-Iz line.
Probably, the current EEGLAB's 2D headplot is slightly more inflated than
this definition.

FYI the citation below is from Oostenveld and Praamstra (2001) p.714.
%%%%%%%%%%%
The placement of electrodes is based on landmarks on the skull,
namely the nasion (Nz), the inion (Iz), and the left and right
pre-auricular points (LPA and RPA). The first step is to form the line
from Nz to Iz, approximately over the vertex. To determine the
location of the vertex, the contour from LPA to RPA is also passed
over the vertex. These two contours should intersect at 50% of their
lengths and the point thus obtained is the exact vertex.  Along the
sagittal Nz-Iz scalp contour over the vertex, the positions Fpz, AFz,
Fz, FCz, Cz, CPz, Pz, POz and Oz are
marked at 10% distances along this antero-posterior contour (Fig. 1).
With position Cz at 50% along this contour, corresponding
to the vertex, the position of Oz is at a distance of 90% from Nz and
10% from Iz.
%%%%%%%%%%%%

Makoto

2014/1/5 Pete Manza <pete.manza at gmail.com>

> Hello,
>
> I've tried to search the listserv but can't seem to find the answer to
> this - I've been trying to use topoplot to generate scalp maps for
> publication (I have a standard 64-electrode montage). However I can't seem
> to get the electrodes/topography neatly inside the outline of the head.
>
> I've tried messing with the "plotrad" and "headrad" options, but it
> doesn't come out well and I know that in doing so I'm making the image
> anatomically incorrect.
>
> So, is there a way to make the image look neat and "bend" the electrodes
> inside the head radius?
>
> It would be nice to get it to look something like figure 4 here:
> http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3114253/
>
> Thanks so much!
> Pete
>
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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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