Dear SPM- and DCM-experts,
by means of DCM I am trying to explore how brain activity induced by experimental pain is influenced by medication. To do this, I defined a model including 4 regions influenced by the medication as evident from GLM and PPI analysis. The driving input consists of the experimental pain stimuli; modulator is the medication (experimental pain stimuli applied under influence of medication).
My aim is to compare modulation of intrinsic connections. However, I am not sure, whether only one or two regions receive driving pain input as both would make sense physiologically.
If I understood correctly, the driving input is needed to “inject activation” into the model system. Bayesian model comparison shows that models that include two regions receiving direct input perform consistently better than models where only one region is receiving driving input. However, I wonder whether this is because these models are more “realistic” or simply because models become better with increasing activation that is put into the system?
Thanks a lot,
carmen
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