[Mne_analysis] weighted MNE units

Alexandre Gramfort alexandre.gramfort at inria.fr
Wed Oct 9 02:02:42 EDT 2019
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hi,

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?
>

yes


> What about the unit, is it indeed Am or should it rather be called an
> arbitrary unit?
>

it is indeed Am when you use MNE.

Alex



>
>
> Best regards,
>
> Anja
>
>
>
> *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
>
>
>
> *        External Email - Use Caution        *
>
> 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.
>
>
>
> HTH
>
> Alex
>
>
>
>
>
>
>
> On Tue, Oct 8, 2019 at 10:15 AM Thiede, Anja <anja.thiede at helsinki.fi>
> wrote:
>
> *        External Email - Use Caution        *
>
> Hi,
>
>
>
> 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
>
>
>
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