[FieldTrip] auditory evoked gamma

[Stephan Moratti]

Dear Nenad,

An alternative could be doing minimum norm on the real and imaginary part of your gamma response and then take the modulus get a measure of absolute power. This works for highly correlated sources see:

1.	Jensen, O. & Vanni, S. A new method to identify multiple sources of oscillatory activity from magnetoencephalographic data. Neuroimage 15, 568-574 (2002).

It should also work for EEG and is easy to implement.

Best,

Stephan

El 08/03/2013, a las 02:16, Robert Oostenveld <r.oostenveld at donders.ru.nl> escribió:

> Hi Nenad
> 
> On 7 Mar 2013, at 7:08, Nenad Polomac wrote:
>> I would like to ask you for a suggestion about localisation o auditory evoked gamma osculations. I checked all tutorials and I haven't found much help. DICS beamformer doesn't work in this case. 
> 
> 
> Please do note that the tutorials are not meant as a complete list of analyses that you can do, but they merely provide a practical starting point. Something not being listed on the fieldtrip wiki does not mean that it cannot be done. 
> 
> One would not expect strong correlations/coherence between auditory activity in the gamma band, so beamforming is from a methodological viewpoint also not as problematic for high frequenies as it is for AEFs. This paper by Till Schneider (http://www.ncbi.nlm.nih.gov/pubmed/18617422) demonstrates that with EEG beamforming of auditory gamma is possible. 
> 
> If you fear for too strong correlations, you can try subsets of channels over both hemispheres. Or use a symmetric dipole pair (cfg.symmetric in ft_prepare_leadfield) as source model.
> 
> best regards,
> Robert 
> 
> 
> 
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________________________________________________________
Stephan Moratti, PhD

see also: http://web.me.com/smoratti/

Universidad Complutense de Madrid
Facultad de Psicología
Departamento de Psicología Básica I
Campus de Somosaguas
28223 Pozuelo de Alarcón (Madrid)
Spain

and

Center for Biomedical Technology
Laboratory for Cognitive and Computational Neuroscience
Parque Científico y Tecnológico de la Universidad Politecnica de Madrid
Campus Montegancedo
28223 Pozuelo de Alarcón (Madrid)
Spain


email: smoratti at psi.ucm.es
Tel.:    +34 679219982


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