DICS power

jan-mathijs schoffelen j.schoffelen at PSY.GLA.AC.UK
Thu Aug 14 12:18:43 CEST 2008


Dear Cristiano,

This issue is covered in the 'applying beamforming techniques in the
frequency domain'-tutorial on the fieldtrip-website.
This is perfectly normal behaviour of the beamformer, when you use
non-normalized leadfields (which I would do in the first place).
In order to make sense out of the power-images you can do two things:
-plot the power relative to another 'condition' (this is explained in
the tutorial)
-compute the 'neural-activity-index'  (this is also explained in the
tutorial)
Please have a look there, it might already clear things up for you.

Yours,

Jan-Mathijs

On Aug 14, 2008, at 12:11 PM, Cristiano Micheli wrote:

> Hi All
> I have a problem with DICS's power and my simulations. I simulate an
> external virtual channel coupled with MEG activity in a specific
> frequency
> band (around 20 Hz).
> I use DICS and submethod 'ref_chan'  and i can localize 1 source
> (even 2 if
> they are distant) but only if I use coherence as a functional
> parameter and
> reducerank=2.
> With power i always see a bright spot in the middle of the brain.
> Should i select some options to account for decreased sensors'
> sensibility
> in depth?
> Since I used anyway coherence parameter for localization I did not pay
> attention to this before but somehow it looks strange to me.
> I attach the code and power image.
> Regards
>
>     cfg           = [];
>     cfg.grid      = grid_;
>     cfg.method    = 'dics';
>     cfg.projectnoise = 'yes';
>     cfg.reducerank = 2;
>     cfg.lambda    = 0;
>     cfg.refchan   = refch;
>     cfg.frequency = 20;
>     cfg.hdmfile   = 'myheadmodel.hdm';
>     sourcecond    = sourceanalysis(cfg, freqcond);
>
>
>
> ----------------------------------
> The aim of this list is to facilitate the discussion between users
> of the FieldTrip  toolbox, to share experiences and to discuss new
> ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/
> archives/fieldtrip.html and http://www.ru.nl/fcdonders/
> fieldtrip.<power.png>

----------------------------------
The aim of this list is to facilitate the discussion between users of the FieldTrip  toolbox, to share experiences and to discuss new ideas for MEG and EEG analysis. See also http://listserv.surfnet.nl/archives/fieldtrip.html and http://www.ru.nl/fcdonders/fieldtrip.



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