[FieldTrip] Virtual Electrodes

[Hesham ElShafei]

Hello fieldtrippers ,

For my Phd , I am trying to investigate the dynamics of alpha
oscillations during anticipatory attention. I have analysed the data in
the sensor level and based upon these analyses I have define
time-frequency windows of interest to which I have applied the DICS
beamformer.

Based on statistical results, I have defined regions of interest (the
left Heschl Gyrus, for example). Now I would like to have a look at the
time couse of these sources.

I have followed this tutorial:
http://www.fieldtriptoolbox.org/tutorial/salzburg?s[]=virtual&s[]=sensors

However, there is a step I would like to expert opinions. In the
tutorial, after having defined voxels of interest , they have
re-calculated the leadfield for these voxels. (let's call that method A)

Should this operation be different to Method B which involves marking
only the voxels of interest in the leadfield (that has been used for the
DICS) as inside  the brain?

I've tried both methods, and results are different. So I would like to
know why such difference exists and which is method is better?

Also in the aforementioned tutorial , there is this:

cfg.grid.pos=[btiposCML;btiposHGL;btiposHGR]./1000; % units of m

Which I don't think is correct since conversion should be done from mm
to cm (if we follow the tutorial)

Thank you very much

Hesham ElShafei 
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