[FieldTrip] What does minimum-norm estimate tell me + correlation in the source space

[Harold Cavendish]

Dear Runnan,

I'd be happy to help, but sadly, I have no experience with FreeSurfer and
skipped that portion of the tutorial entirely (instead, I used files from
fieldtrip/template).

However, using just common sense, I believe there's an error in the
tutorial because orig-nomask.mgz is mentioned for the first time where you
need to load it but it isn't present in any of the outputs or in the
Subject01 directory. I believe it's just a renamed copy of orig.mgz which
is created as explained in the tutorial.

As far as I understand, you take an anatomical MRI image (e.g.
Subject01.mri), use FT to do some preprocessing and get Subject01.mgz (a
FreeSurfer-compatible format), then do some segmentation and get
Subject01masked.mgz, then do some conversion in FreeSurfer and transform
those two into orig.mgz and brainmask.mgz respectively, and to make it even
more convoluted, some filled.mgz pops up as well. To be honest, I don't
follow… I have zero experience with FreeSurfer as well as MRI/fMRI analysis.

*Briefly, try using orig.mgz instead of orig-nomask.mgz whenever you need
to use ft_read_mri('orig-nomask.mgz'). If it doesn't do the job, hopefully
someone else will come to the rescue.*

Best regards,
Harold


On 12 March 2016 at 01:02, <runna90 at 126.com> wrote:

> Dear Harold,
> I am very sorry that I am not writing to reply your question but to
> request you something about minimum norm estimate because I am a rather new
> fieldtripper. I noticed that you have got results applying MNE, thus I
> think you must be more experienced! I followed the tutorial at
> http://www.fieldtriptoolbox.org/tutorial/minimumnormestimate and did
> source reconstruction with  MEG data acquired from ctf 275 system. But I
> got stuck in here
> . Source model: Co-registration of the source space to the sensor-based
> head coordinate system,
> I could not find the file named ‘orig-nomask.mgz’ under the mir folder.
> Would you tell me in which step should this file be created? And how to
> create this file?
>
> Best regards,
>
> Runnan
>
>
>
>
>
>
> 在 2016年3月10日，08:40，Harold Cavendish <harold.cav89 at gmail.com> 写道：
>
>
> Dear FieldTrip users,
>
>
> I have a few questions regarding source localisation and statistics:
>
>
> 1. Suppose I'm doing source reconstruction of ERP using minimum-norm
> estimate; one condition, multiple subjects. I'm using ft_sourceanalysis()
> and getting rather meaningful results which I visualise via ft_plot_mesh().
>
>
> What is the validity of this result? I understand there are many
> individual dipoles spread over the cortical sheet and we're estimating best
> fit to the data given the conductance model while minimising overall power,
> but what does this actually tell us? If I find an area with higher power,
> what conclusions can I draw?
>
>
> 2. Can I compute a correlation between the result in the source space and
> a behavioural variable? Perhaps even specify a region of interest? If yes,
> is this approach considered to be valid?
>
>
> I want to see if e.g. the power of the reconstructed activity in the
> source space averaged over a time window correlates with my behavioural
> variable.
>
>
> Thank you!
>
>
> Best regards,
>
> Harold
>
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