[FieldTrip] About source reconstruction outputs

[ivano triggiani]

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*
> _______________________________________________
> fieldtrip mailing list
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fmailman.science.ru.nl%2Fmailman%2Flistinfo%2Ffieldtrip&data=05%7C02%7Cfieldtrip%40science.ru.nl%7C3bf1d8ed1b06478ecda508de3cec4348%7C084578d9400d4a5aa7c7e76ca47af400%7C1%7C0%7C639015182611973463%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=BTWE03k0WEH%2BT9FANReruMVrSJEBi6h89XPCtcG3dH8%3D&reserved=0
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fdoi.org%2F10.1371%2Fjournal.pcbi.1002202&data=05%7C02%7Cfieldtrip%40science.ru.nl%7C3bf1d8ed1b06478ecda508de3cec4348%7C084578d9400d4a5aa7c7e76ca47af400%7C1%7C0%7C639015182611993754%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=nOi9L5obF1t2RexwBytuFW9BbMpU8x3ycPK797H%2BGRA%3D&reserved=0
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.science.ru.nl/pipermail/fieldtrip/attachments/20251216/c7e3a502/attachment.htm>