[Mne_analysis] weighted MNE units

Thiede, Anja anja.thiede at helsinki.fi
Wed Oct 9 01:55:01 EDT 2019
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Thank you Alex for your fast reply! If I understood correctly, then these small values are indeed correct and should be comparable to others obtained with the same method (e.g. for group comparisons), even if they are not the absolute amplitudes. Is that correct? What about the unit, is it indeed Am or should it rather be called an arbitrary unit?

Best regards,

From: mne_analysis-bounces at nmr.mgh.harvard.edu [mailto:mne_analysis-bounces at nmr.mgh.harvard.edu] On Behalf Of Alexandre Gramfort
Sent: tiistaina 8. lokakuuta 2019 11.51
To: Discussion and support forum for the users of MNE Software <mne_analysis at nmr.mgh.harvard.edu>
Subject: Re: [Mne_analysis] weighted MNE units

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Dear Anja,

MNE promotes sources with minimal energy / variance. This leads
to a bias in the estimated amplitudes. If you care about absolute
amplitudes you should have a look at dipole fits or sparse solvers
that estimate multi-dipole configurations.


On Tue, Oct 8, 2019 at 10:15 AM Thiede, Anja <anja.thiede at helsinki.fi<mailto:anja.thiede at helsinki.fi>> wrote:

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I am using MNE Python to do source modeling with weighted MNE and am wondering about very small units of the sources. This is something that I have found with my own data and could reproduce the issue using the sample data: https://github.com/athiede13/speech_sources/blob/master/weighted_MNE_sample.py

While I would expect source activations in the range of 30-60 nAm (for example as in dipole solution https://mne.tools/stable/auto_examples/inverse/plot_mixed_norm_inverse.html that uses the same data), what I get are values in the range of 0.3-0.6 nAm. So there seems to be a difference of 2 orders of magnitude. Do you know where this could come from? I have pondered about this for a while and cannot find the source of the difference.

Thanks for having a look and I hope that we can figure it out!

Best regards,
Anja Thiede

Anja Thiede, M.Sc.
Doctoral student
Cognitive Brain Research Unit
Department of Psychology and Logopedics
Faculty of Medicine
University of Helsinki
E-Mail: anja.thiede at helsinki.fi<mailto:anja.thiede at helsinki.fi>

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