[Eeglablist] Channels for ICA

[Makoto Miyakoshi]

Dear Fabio,

> I have a (probably naive) question regarding ICA.

I'll give you my naive answers, not intentionally but due to my
limitations. Follow them at your own risk.

> - whether I should or not choose the whole 128 channel set for running ICA

Yes, unless your data is too short for that. Remember, (number of
channels)^2 x 30 data points at 256 Hz sampling rate is a rule of thumb for
running ICA.

> - consequently, how I should *a priori* decide which channels to consider
for ICA and which not.

You can determine a priori which anatomical regions you are going to
analyze. Then, if ICA gives you the '(stationary) effective source
locations' that overlap /are close enough to those pre-selected regions,
pick them up for the final analysis.

ICA is a hypothesis-free approach, but that does not mean you cannot have a
hypothesis.
You might enjoy reading the classic discussion between ICA pioneers and
Karl Friston about how ICA could be used in neuroscience data analysis.
Friston KJ. Modes or models: a critique on independent component analysis
for fMRI. Trends Cogn Sci.  1998. Oct 01; 2(10) 373-375

> The recordings are ~2 minutes long and the sampling rate is 1000 Hz.

If you have only 2 min, you definitely cannot perform >100ch ICA.
sqrt(250 Hz x 120 sec / 30) is about 31, so you want to use 'pca' option to
perform dimension reduction to obtain 31 ICs.

> I would like to keep as many channels as possible during pre-processing,
and afterwards discard the ones I realize are not useful to my analysis -
if this approach seems reasonable.

Record longer. 2-min EEG is too short if you want to use ICA.

Makoto

On Thu, Jul 19, 2018 at 3:26 AM Giatsidis, Fabio <fabio_giatsidis at brown.edu>
wrote:

> Hello EEGLAB list,
>
> I have a (probably naive) question regarding ICA.
> I have been using an EGI 128-channel system to record resting states. I
> have been reading a bit about ICA, but it is still not clear to me:
> - whether I should or not choose the whole 128 channel set for running
> ICA, and
> - consequently, how I should *a priori* decide which channels to consider
> for ICA and which not.
>
> The recordings are ~2 minutes long and the sampling rate is 1000 Hz. I
> would like to keep as many channels as possible during pre-processing, and
> afterwards discard the ones I realize are not useful to my analysis - if
> this approach seems reasonable.
>
> Also:
> - if as a very first step I delete some clearly bad channels and then
> interpolate them to repopulate the original channel set, is it legit to
> include such interpolated channels during ICA?
>
> Thank you very much!
> Best,
> -Fabio
>
> --------------------------------
> *Fabio Giatsidis, M.D.*
> Resident in Neurology - University of Rome "Tor Vergata" - Rome, Italy
> Post-doctoral research fellow - Brown University - Providence, RI, USA
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-- 
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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