[Eeglablist] ICA of the evoked gamma?

Makoto Miyakoshi mmiyakoshi at ucsd.edu
Tue Jul 8 11:19:17 PDT 2014

Dear Nenad,

If you average across trials that have same temporal structures that should
be fine.

I haven't seen a gamma decomposed as a separate IC, but it has been always
accompanied by theta. That means, if theta were not decomposed well, there
would not be clear gamma found in ICs. There are several reasons I can
think of to explain it... one is the low amplitude, second is the small
local activation (i.e. not widely volume conducted), etc.


On Mon, Jul 7, 2014 at 2:00 PM, Nenad Polomac <polomacnenad at gmail.com>

> Hi everybody,
> I am interested in evoked gamma band response. I would like to extract the
> independent components from my EEG data which represent this effect. My
> idea was to calculate the ICA on my 60 channel EEG single trials and then
> to average the time-courses each of the components over trials. Then on
> this evoked trial I would calculate time frequency with the Morlet wavelet
> and obtain evoke power each of components (freq wise baseline correction as
> well). Finally, those components that have in a particular time window
> increase in power relative to baseline would be considered as the one that
> represent gamma band response. I would use these info for the rejecting of
> all other components from the original (non averaged) ICA data. After that
> I would back project remaining (gamma representing) components into the
> channels. My question would be, is this ok to do from the mathematical
> point of view? I am particularly asking about the step where time-courses
> each of the components is averaged over trials.
> I would really appreciate some opinions and experiences.
> All the best!
> Nenad
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Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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