[FieldTrip] About source reconstruction outputs

[Fabio Strappazzon]

Ciao Ivano,
thank you for your anwer.

1) As expected, thanks.

2) Your solution would be fine but the problem is that for each dipole I
have a 3 x pnts array (orientation x time points) and I do not know how
FieldTrip would take care of that. But even trying to using classical
MATLAB function like pwelch (as I'm curretly doing) I'm not super sure how
should I proceed: should I calculate a separate PSD for orientation? And
then what: summing across orientation? Taking the average? Taking the
squared root of sum?

Thank you for your help

Il giorno mar 16 dic 2025 alle ore 22:44 ivano triggiani <
ivanotriggiani at gmail.com> ha scritto:

> Caro Fabio,
>
> My humble opinion:
>
> 1. Since source reconstruction is a well-known ill-posed problem, every
> method relies on different constraints. For instance, MNE minimizes the
> overall L2 norm, which often results in smooth solutions, easily distorted
> if noise is significant.
>
> To stabilize the solution, regularization methods use, for example,
> estimation of the noise covariance and a regularization parameter. This
> scaling process changes the output, which is no longer strictly measured in
> physical units (like current density) but is reported in a.u. or normalized
> quantity. sLORETA and eLORETA operate under a similar concept of weighted
> or standardized normalization (I am simplifying!).
>
> 2.  I think so, but you must calculate the PSD on the estimated source
> time series. For distributed solutions the data is contained in the
> source.avg.mom field, not source.avg.pow, if I remember correctly.
> You need to restructure the source.avg.mom field so that FieldTrip treats
> each source location as a separate "channel" before running ft_freqanalysis.
> Something like:
>
> cfg = [];
> cfg.method = 'mtmfft'; % or whatever
> cfg.output = 'pow';
> cfg.foi = 0.5:0.5:40; % freqs
> freq_source = ft_freqanalysis(cfg, source_data);
>
> The resulting PSD may look "weird" compared to sensor-level data because
> the spatial filter (source method) affects the spectral profile of the
> noise and signal.
> Ciao,
>
> Ivano
>
> ---
>
> *A. Ivano Triggiani, Ph.D.*
>
>
> ________________________________________________
>
>
>
> On Tue, Dec 16, 2025 at 11:55 AM Fabio Strappazzon via fieldtrip <
> fieldtrip at science.ru.nl> wrote:
>
>> Dear all,
>>
>> I'm currently using wMNE as inverse operator.
>> I would like to know two things:
>>
>> 1) What are the units of measure of source reconstructed activity? I see
>> that many papers report them as arbitrary units (a.u.) but I would like to
>> know more why is that the case.
>>
>> 2) Would it be possible to still apply the FieldTrip functions for
>> calculating PSDs (ft_freqanalysis) on outputs from source recontructed data
>> with distributed apporaches (like MNE) or there are some specific functions
>> for those kind of data? If so, on which outputs are calculated: on the
>> source.avg.mom or the source.avg.pow?
>>
>> Many thanks,
>>
>> --
>> *Strappazzon Fabio, *
>> *PhD Student at ITAB (Institute for Advanced Biomedical Technologies) -
>> Chieti*
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-- 
*Strappazzon Fabio, *
*PhD Student at ITAB (Institute for Advanced Biomedical Technologies) -
Chieti*
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