First, the bilinear models could be either "full connectivity," with all possible endogenous connections, or the connectivity could be sparse.
Compared to the most complex Model 1, which included condition-dependent modulation of all endogenous connections, Model 4 did not comprise modulation of connectivity between PFC or M1 and subcortical regions (putamen, thalamus, cerebellum) as a function of the experimental conditions (Fig. 3).
DCM parameters include exogenous inputs, endogenous connections, bilinear, and nonlinear modulatory connections.
Endogenous connections reflect directed coupling among areas, averaged over experimental conditions.
Posterior parameters after Bayesian model averaging for driving inputs and endogenous connections are depicted in Table 1.
In this study, we focused on the fear-induced modulation of visual-limbic-prefrontal connections (modulatory effect), but also examined heroin effects on endogenous connections and driving inputs.
All 40 models shared the same endogenous network structure but differed in the modulation of these endogenous connections as a function of condition.
Starting from this initial model, we created three different variations per model, in which fearful faces (modulatory effect) were allowed to modulate the endogenous connections (Fig. 1B).
For endogenous connections, positive values indicate that as activity increases in the originating region, the rate of change in activity in the target region also increases.
There were no other significant endogenous connections (i.e. from any of the regions to V1 or from SMG to pOp or pOp to SMG).
