[Eeglablist] pre-processing for sLORETA and connectivity analysis

[Iman Mohammad-Rezazadeh]

If i may chim in i would suggest to check the  Brainstorm website and some papers re your questions.

As my friend, Makoto suggested you should be concerned to use filters with phase shift if you are doing sort of effective connectivity analyses.  Check out the paper from Robert Coben and me re this issue.

Best
Iman

Iman Rezazadeh, PhD
UCLA SCHOOL OF MEDICINE

________________________________
From: eeglablist-bounces at sccn.ucsd.edu <eeglablist-bounces at sccn.ucsd.edu> on behalf of Makoto Miyakoshi <mmiyakoshi at ucsd.edu>
Sent: Monday, January 11, 2016 6:36:56 PM
To: Mina Marmpena
Cc: EEGLAB List
Subject: Re: [Eeglablist] pre-processing for sLORETA and connectivity analysis

Dear Mina,

> I wonder if the filter I will choose for the pre-processing of my EEG data will affect significantly the result of sLORETA source localization and connectivity analysis afterwards.

I've never used sLORETA but I guess you need to choose a single frame from which inverse problem is solved... if this is the case, filtering as well as averaging window length (and timing of course) would significantly affect the result.

> So far I use IIR filter as EEGLAB plugin, with a 0.5-40?z band-pass and all the default parameters. Do you think this should be OK or should I use another filter?

I don't use IIR myself but unless your data are horribly screwed up using IIR should be fine.

> I've seen Makoto's notes on filtering and connectivity analysis but it addresses Granger causality in particular, and in my case we are interested in functional connectivity analysis so I am not so sure if it applies.

Unless you do multivariate Granger, I recommend you perform our standard FIR 1-50 (or 100, 250 etc) filter. Note that EEGLAB's '1-Hz filter' is 0.5 Hz cutoff at -6dB.

> Also I would like to ask you for the same analysis framework, whether a Surface Laplacian filtering, as a final step in the pre-processing, works well with sLORETA or it is something I should avoid.

The assumption in using surface laplacian is that EEG sources are all radial, which I don't understand. I've seen many tangential scalp topography in ICA results. But, that being said, it isn't a terribly bad idea to apply it since there are much more radial sources.

Good luck!

Makoto


On Fri, Jan 8, 2016 at 8:44 AM, Mina Marmpena <mina.marmpena at gmail.com<mailto:mina.marmpena at gmail.com>> wrote:
Dear EEGLAB list,

I wonder if the filter I will choose for the pre-processing of my EEG data will affect significantly the result of sLORETA source localization and connectivity analysis afterwards.

So far I use IIR filter as EEGLAB plugin, with a 0.5-40?z band-pass and all the default parameters. Do you think this should be OK or should I use another filter? I've seen Makoto's notes on filtering and connectivity analysis but it addresses Granger causality in particular, and in my case we are interested in functional connectivity analysis so I am not so sure if it applies.

Also I would like to ask you for the same analysis framework, whether a Surface Laplacian filtering, as a final step in the pre-processing, works well with sLORETA or it is something I should avoid.

Finally, I was wondering if you could suggest some papers or resources with sLORETA and connectivity analysis that could help me to better understand how to deal with this kind of analysis, especially how to derive a connectivity measure from the current densities.


Thank you in advance,
Mina

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--
Makoto Miyakoshi
Swartz Center for Computational Neuroscience
Institute for Neural Computation, University of California San Diego
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