Yes, that's what I meant.
Vladimir
2011/6/15 飞鸟 <[log in to unmask]>:
> Dear Vladimir,
> Considering the complexity and reliability, I am trying to cut a big loop
> into pieces, and then select a part of the big loop to continue my research.
> Thus, I try to regard the thalamus as begining region that receive the
> extrinsic input.
> You mean I might only need to consider cingulate cortex and frontal
> cortex?
>
> Haoran.
>
> At 2011-06-15 20:10:30,"Vladimir Litvak" <[log in to unmask]> wrote:
>
>>Yes, that is OK. However, just for the input it is not necessary to
>>model the thalamus, since the input models thalamic input to the
>>cortex anyway and not sensory input. You might need to model the
>>thalamus if you think that two cortical regions communicate via
>>cortico-thalamo-cortical pathway.
>>
>>Vladimir
>>
>>2011/6/15 飞鸟 <[log in to unmask]>:
>>> Dear Vladimir,
>>> As for the region(s) that receive extrinsic input, should it (they) be
>>> no-hidden sources? Or it just doesn't matter? Take an example:
>>> input---->Thalamus---->Cingulate cortex---->Frontal cortex If the
>>> extrinsic input arrives at thalamus(hidden source) first, is it ok?
>>> Thank you! Best regards!
>>> Haoran.
>>>
>>>
>>>
>>> At 2011-06-14 23:33:55,"Vladimir Litvak" <[log in to unmask]> wrote:
>>>
>>>>I suspect it might be problematic but it also depends on how your
>>>>sources are connected. For instance if you have V1 as your non-hidden
>>>>source that receives input and is connected to hippocampus and
>>>>amygdala, this is not a good model because there is nothing that
>>>>constraints the estimation of your hidden source activity. Usually the
>>>>model will only be meaningful if you have non-hidden sources that
>>>>receive inputs via hidden sources.
>>>>
>>>>Best,
>>>>
>>>>Vladimir
>>>>
>>>>2011/6/14 飞鸟 <[log in to unmask]>:
>>>>> Dear Vladimir,
>>>>> Thanks for your quick and detailed reply, I understand that much. How do
>>>>> you think if I have 1 non-hidden source and 2 hidden soruces?
>>>>> Thanks!
>>>>> Haoran.
>>>>>
>>>>> At 2011-06-14 23:11:18,"Vladimir Litvak" <[log in to unmask]> wrote:
>>>>>
>>>>>>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
>
>
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