Dear Peter,
thanks a lot for your reply!
the experimental and the control session consisted of multiple stimulation blocks interspersed by rest. The difference between both session was that patients perceived an additional percept during the experimental session which was absent in the control session.
The intensity of the additional percept was rated block-wise.
I'm not sure if I can formulate an explicit DCM model with my a priori ROIs due to the fact that the perception of the additional percept in the experimental condition temporally coincides with the temporal course of the stimulation in the experimental condition (the additional percept is only perceived during stimulation but not rest). Moreover, the intensity of the additional percept during the experimental session is quite homogeneous within a subject (across blocks) and varies only across subjects when using the average intensity. Thus a weigthing procedure is not very promising to dissociate brain-activity related to the stimulation versus the intensity of the additional percept.
I'm interested to know if I can identify effective connectivity reflecting the additional percept with our experimental paradigm. I thought about session concatenation using stimulation as a direct input during both sessions and to model the additional percept only during the experimental condition.
However, I'm not sure if the high temporal coincidence between the stimulation and the additional percept regressor will cause problems. Using the rating values seems to be only promising across subjects, but might reflect merely 'magnitude coding' which is not specific to the additional percept. Thus a simple comparison between the experimental and control session seems to be more promising.
Many thanks for any helpful comment on that
Best,
Chris
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