If we perturb this system with two perturbations here,
we have u1 which affects region 1 and
u2 which affects the relationship between regions 1 and 2.
Then, basically what we do is this gives rise to changes in the neuronal
activation, which in turn, which we can't measure,
which is latent to us because we can't measure that with fMRI.
But in turn this gives rise to changes in the hemodynamic response
which we denote by y1 and y2 which we can measure.
So the whole idea here is that we propose a model like this.
And then we perturb the system, and then we measure the hemodynamic response.
And then we try to back track and figure out what was the underlying latent
neural activation that could have given rise to this hemodynamic response.
So that's sort of the general idea behind DCM.
And so basically one uses a bilinear state equation to model
a cognitive system at the neuronal level.
And the modeled neuronal dynamics is then transformed into BOLD signals using
a hemodynamic forward model.
And we'll talk about all these things in a later module.