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

[Eric Larson]

You could use Euclidean distance to identify neighbors on the medial wall,
too. I have some code somewhere experimenting along those lines if you want
it.

Eric



On Sun, Aug 24, 2014 at 1:58 PM, Hari Bharadwaj <hari at nmr.mgh.harvard.edu>
wrote:

> Hmm.. BA18/19/37  on the left and right hemispheres are not that far from
> each other... Funny things could happen if the activation is bilateral,
> especially if there are phase/latency differences between hemispheres...
>
> Perhaps you could look for arguments along the lines presented here:
> http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2797557/#!po=2.17391
>
> Hari
>
> On Aug 24, 2014, at 2:59 PM, Denis-Alexander Engemann <
> denis.engemann at gmail.com> wrote:
>
> 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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