[FieldTrip] auditory evoked gamma

smoratti at psi.ucm.es smoratti at psi.ucm.es
Sat Mar 9 02:11:11 CET 2013

```Dear Don,

I have done it using Brainstorm (sorry Fieldtrippers) as in Brainstorm minimum norm in the frequency domain is implemented. But as the minimum norm estimate (MNE) is applied to each time point I guess the following approach should easily work:

Create a data structure that you normally feed into the minimum norm algorithm with source analysis.
The data structure has two time points.
Copy the real and imaginary part into the two time points each.
Run the minimum norm estimate on that data structure (I guess you will have to estimate some noise covariance matrix from a baseline or so before).
Then, take the modulus of the minimum norm estimates across the two "time points" (that include the inverse real and imaginary part).

I have never tried it with field trip and the approach above is just an idea. I am happy of any feedback if it works or if there is a more elegant solution.
Sorry that I don't have a "fixed" solution. I will try it myself.

I hope I could help.

Best,

Stephan

________________________________________________________
Stephan Moratti, PhD

Departamento de Psicología Básica I
Campus de Somosaguas
Spain

and

Center for Biomedical Technology
Laboratory for Cognitive and Computational Neuroscience
Campus Montegancedo
Spain

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

El 08/03/2013, a las 17:48, Rojas, Don escribió:

> 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:
>
>>
>> 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:
>>
>>>
>>> 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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>>> fieldtrip at donders.ru.nl
>>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>>
>>
>> ________________________________________________________
>> Stephan Moratti, PhD
>>
>>
>> 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
>> Campus Montegancedo
>> 28223 Pozuelo de Alarcón (Madrid)
>> Spain
>>
>>
>> email: smoratti at psi.ucm.es
>> Tel.:    +34 679219982
>>
>>
>> _______________________________________________
>> fieldtrip mailing list
>> fieldtrip at donders.ru.nl
>> http://mailman.science.ru.nl/mailman/listinfo/fieldtrip
>
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