Dear Aif, Christian:
Some notes to the SPM list suggest that DCM can be used with sparse sampling.
See
https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind0810&L=SPM&P=R65325
https://www.jiscmail.ac.uk/cgi-bin/webadmin?A2=ind05&L=SPM&P=R234275
(There was a message from Will Penny in 2004 that said sparsely
sampled data could not be used with DCM, but that was superseded by
the above messages).
The lack of connectivity (i.e., I assume you mean non-significant
connection parameters) can happen for many reasons including whether
your model is appropriate for your data, how you setup your model
(e.g., don't forget to include driving inputs), whether activity in
the regions is related to the task, etc.
Darren
On Tue, Nov 24, 2009 at 5:27 AM, Grefkes, Dr. Christian
<[log in to unmask]> wrote:
> Dear Aif,
>
> TR is too long...DCM is not really suited for sparse sampling as DCM works
> with continuous image acquisition (assuming continuous time)...if you reduce
> the TR to TA you will see that there are some connectivity estimates, but
> obviously they are of reduced validity...
>
> Christian
>
> --------------------------------------------------
> Dr. Christian Grefkes
>
> Klinik und Poliklinik für Neurologie
> Universität zu Köln
> Kerpener Straße 62, 50924 Köln
> phone: +49-221-4726-310
> fax: +49-221-478-7005
> http://cms.uk-koeln.de/neurologie/content/mitarbeiter/index_ger.html
>
>
> Max-Planck-Institute for Neurological Research
> Neuromodulation & Neurorehabilitation
> Gleueler Str. 50, 50931 Köln
> phone: +49-221-4726-310
> fax: +49-221-4726-298
> http://www.nf.mpg.de/index.php?id=255
>
> aini ismafairus abd hamid <[log in to unmask]> hat am 24. November 2009 um
> 09:45 geschrieben:
>
>> Dear SPMers,
>>
>> I use Sparse Paradigmn. Attached is my paradigmn.I try to do DCM but no
>> connectivity. Why this happen? Is it because of model specification in 1st
>> level problem or because of the selection of region?
>>
>> My 1st level/ model specification:
>> TR=16s
>> microtime resolution: 96 (consider 6 time bins in 1 second TR)
>> mocrotime onset : 81
>>
>>
>> Regards,
>> AIF
>>
>> Dear SPMers,
>>
>> I use Sparse Paradigmn. Attached is my paradigmn.I try to do DCM but no
>> connectivity. Why this happen? Is it because of model specification in 1st
>> level problem or because of the selection of region?
>>
>> My 1st level/ model specification:
>> TR=16s
>> microtime resolution: 96 (consider 6 time bins in 1 second TR)
>> mocrotime onset : 81
>>
>>
>> Regards,
>> AIF
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