Dear Luke,
Following Darren's comprehensive reply, just a small additional comment:
If you do not want to concatenate your data and your sessions are
perfectly identical, then it should be possible, in principle, to
average the data and run a single DCM on the averaged time
series. The necessary VOI file would have to be manually specified, however.
Another (and possibly better) option is to analyse each session
separately with DCM and then feed the resulting parameter estimates
into an appropriate second level model which takes into account that
multiple estimates belong to the same subject (i.e. a repeated measures ANOVA).
Best wishes,
Klaas
At 18:25 17/06/2007, you wrote:
>For some reason, the original message was not included with my reply.
>Please see the issue below. Thanks.
>
>DCM mavens:
>
>We have collected 6 runs (not repetitions) of block-design fMRI data for
>each subject. I want to test a model using DCM including the data from all 6
>runs. In a PPI analysis, this was simple...I would extract the time series
>for a given VOI (using the same seed voxel and sphere dimensions) for each
>run separately and create a model including 6 sessions. However, it does not
>appear to be that simple using DCM in SPM5. I have read through the postings
>about this issue and one solution I have found suggests concatenating the
>data from the 6 sessions and including 2 regressors, one for the session
>number (i.e., 1..2..3..4..5..6) and one for the transition period
>(specifying the last time point in a session and the first time point in the
>following session). Is it necessary and/or appropriate to do this? It seems
>more appropriate and straightforward to take the mean of the time series
>from each session for each of my VOIs to include in the analysis in a way
>similar to the PPI approach. However, this was not easy to implement within
>the DCM architecture within SPM5.
>
>Suggestions?
_____________________________________
Klaas Enno Stephan, MD PhD
Senior Research Fellow, IoN
Wellcome Trust Centre for Neuroimaging
Institute of Neurology (IoN)
12 Queen Square, WC1N 3BG, London, UK
phone: +44-207-8337481
fax: +44-207-8131420
web: http://www.fil.ion.ucl.ac.uk/~kstephan/
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