[Mne_analysis] Changes of laterality when comparing sensor space to source space cluster solutions

[Denis-Alexander Engemann]

Hi Hari,

I'm personally not too surpised as well. I often see cluster solutions with
bilateral activaiton where only one of the clusters survives the
permutation test. The connectivity constrain that's currently implemented
in MNE-Python would disconnect such bilateral activations easily.
Especially for weak effects that lead to 1-cluster solutions. That being
said it's actually surprising that I do see any results in sensor-space
since no position-correction was available for the system + data-set I'm
currently working with.
But I'm trying to collect some arguments that you can use to explain this
phenomenon to fMRI experts that haven't used MEG. And of course trying to
rule out stupid mistakes on my end.
In this case we're talking about visual activation at the border between
BA18 and BA37.

- Denis


2014-08-24 20:51 GMT+02:00 Hari Bharadwaj <hari at nmr.mgh.harvard.edu>:

> Hi Denis,
>     Is this MEG or EEG data? Perhaps sone examples plots of what you mean
> by changes in laterality would be useful...
>
> Sometimes our intuition (or at least mine) about what field patterns
> correspond to what source patterns can be quite off. This is particularly
> true when looking at fields that are not classic dipole like...
>
> That said, sometimes p-values can be unpredictably high in source regions
> where the projected signal is small (and hence low across permutation
> variance)..e.g., deep sources like the insula or the cingulate often tend
> to show up...
>
> Hari
>
> > On Aug 24, 2014, at 2:36 PM, Denis-Alexander Engemann <
> denis.engemann at gmail.com> wrote:
> >
> > Dear list,
> >
> > I'm currently seeing funky changes of laterality for some contrast of
> interest when comparing cluster permutation solutions between sensor space
> and source space. Does this ring a bell fo anybody? Input would be
> appreciated.
> >
> > Cheers,
> > Denis
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