[FieldTrip] auditory evoked gamma

[Rojas, Don]

Dear Stephan,

If I may ask, have you implemented this approach successfully in Fieldtrip? I agree that it can work well for auditory gamma, but have only done this in BESA. The minimumnormestimate.m function in FT is a time domain only technique as far as I know. If you have done this in Fieldtrip and can provide some guidance, I would very much appreciate the pointers.

Best,

Don

On Mar 8, 2013, at 12:51 AM, Stephan Moratti wrote:

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<mailto: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)
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email: smoratti at psi.ucm.es<mailto:smoratti at psi.ucm.es>
Tel.:    +34 679219982


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