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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