Dear Haoran,
2011/6/14 飞鸟 <[log in to unmask]>:
> Dear Vladimir,
> With regard to hidden source, I still have several simple questions. In
> the paper(David O, etc. 2011) you recommended to me the last time, David
> specify the hidden source's coordinate as [0 0 0]. However, you suggest that
> we can specify the position further that 200mm from
> the origin (like [300 300 300]). Are there any differences between [0 0 0]
> and [300 300 300]?
That research was done with older SPM. The [0 0 0] trick works only
with single sphere model for MEG, but setting coordinates to a large
number works for any head model and the effect is the same.
> I don't know whether this is ture or not: as for any subcortical
> regions, if I want to specify them as hidden sources, I just need to plus
> 200mm to their coordinates respectively(e.g. Cingulate [0 36 28] , change to
> [200 236 228] )?
You just need to set the coordinates to a large number, like [300 300
300]. There is no need to use different coordinates for different
sources, the effect will be the same.
> Further, could I specify two or more hidden sources in my model? If so,
> how can I specify the coordinates for them? Set both of them to [0 0 0] or
> others?
You can use [300 300 300] for all your hidden sources. You can have
more than one but remember that you must also have non-hidden sources
with some meaningful connectivity to the hidden sources. Otherwise you
won't be able to get something meaningful from the model. I'd also not
exaggerate with the hidden source. 5 non-hidden, 1 hidden is OK, but 5
hidden 1 non-hidden is unlikely to work.
Best,
Vladimir
> Thank you!
> Best wishes to you!
>
> Haoran.
>
> At 2011-06-11 00:56:11,"Vladimir Litvak" <[log in to unmask]> wrote:
>
>>Dear Haoran,
>>
>>There are two answers to that. The first answer is that whether there
>>is any signal in the MEG from amygdala or hippocampus is subject to
>>debate and there is some evidence in favor of that but it's not
>>conclusive. The second answer is that you can include sources in your
>>DCM model even if there is no signal in the MEG/EEG from these sources
>>and learn something about those 'hidden' source from their
>>interactions with sources that are observed. As an example you can
>>look at http://www.ncbi.nlm.nih.gov/pubmed/21325540 . You can either
>>just place sources e.g. in the hippocampus the usual way or (in an
>>up-to-date SPM) if you specify the position further that 200mm from
>>the origin (like [300 300 300]) the lead field of the source will be
>>set to zero and then it will be truly hidden source. You can compare
>>the two ways with model comparison to see if there is really any
>>evidence for the source being at particular location or not.
>>
>>Best,
>>
>>Vladimir
>>
>>2011/6/9 飞鸟 <[log in to unmask]>:
>>> Dear spm's users,
>>> Thanks for your concern! As DCM for EEG/MEG is based on nerual mass model,
>>> I wonder that can I apply DCM for EEG/MEG to cerebral limbic system( such as
>>> cingulate, hippocampus and amygdala etc). In other words, is it valid to
>>> specify my model not only include cortex regions(e.g. frontal lobe, temporal
>>> lobe etc.), but also include cingulate or other limbic system's regions?
>>> Any help will be appreciated!
>>>
>>> --
>>> Haoran LI (MS)
>>> Brain Imaging Lab,
>>> Research Center for Learning Science,
>>> Southeast University
>>> 2 Si Pai Lou , Nanjing, 210096, P.R.China
>>>
>>>
>
>
>
> --
> Haoran LI (MS)
> Brain Imaging Lab,
> Research Center for Learning Science,
> Southeast University
> 2 Si Pai Lou , Nanjing, 210096, P.R.China
>
>
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