[Eeglablist] CSD maps in STUDY design

[Arnaud Delorme]

Dear Jurgen,

I had not though of that. 
It makes sense since the power spectral estimates are not linear.
I guess Marco would have to transform each of his dataset and then build a STUDY, and compute the spectrum.
Thanks for correcting me,

Arno

ps: the code I sent would still be valid for ERPs in STUDY since ERP scalp topographies are a linear transformation.

On 19 Jan 2013, at 17:39, Craig E. Tenke wrote:

> Dear Arno:
> 
> Your advice to Marco on how to use CSD with spectral data is incorrect. The Laplacian must precede the spectral computation. If the the spectral transformation is done first, the result is not an interpretable CSD. The implications of this error can be quite profound (cf. Fig. 1 of Tenke and Kayser, 2005). As a general rule, a CSD transform can only be applied to linearly-transformed surface potential data to be physiologically meaningful, although the underlying algorithm can be applied to any data, as shown by your example.
> 
> regards from NY,
> 
> Craig Tenke
> Jürgen Kayser
> 
> 
> On 1/18/2013 8:59 PM, Arnaud Delorme wrote:
>> Dear Marco,
>> 
>> based on another email I sent earlier to the list.
>> 
>> % merge all channel location structures for the STUDY
>> mergelocs = eeg_mergelocs(ALLEEG.chanlocs);
>>  
>> % get ERSP results (scalp maps) - for example scalp topography of spectrum in the alpha band
>> [STUDY spec ] = std_specplot(STUDY,ALLEEG,'channels', { mergelocs.labels }, 'topofreq', [8 12]);
>> 
>> then you may use one of the many laplacian function eeg_laplac.m is a good one although you will have to rebuild a dataset to use it. Something like
>> 
>> TMP = EEG(1);
>> TMP.chanlocs = mergelocs;
>> TMP.data = squeeze(spec{1});
>> CSD = eeg_laplac(TMP, 1);
>> 
>> % plot average CSD scalp topography
>> average_CSD = mean(CSD,2); % average across subjects
>> figure; topoplot(average_CSD, mergelocs);
>> 
>> Best,
>> 
>> Arno
>> 
>> <Mail Attachment.png>
>> 
>> On 17 Jan 2013, at 13:56, Marco Montalto wrote:
>> 
>>> Dear List,
>>> 
>>> Is there a way of producing CSD (current source density) maps in EEGLAB, in a STUDY design?
>>> 
>>> Marco Montalto
> 

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