Figure 2.

This figure illustrates the cognitive and functional anatomy implied by the variational Bayesian inversion of the generative model in the previous figure. Here, we have associated the Bayesian updates of expected states with perception, of future control states (policies) within action selection and, finally, expected precision with evaluation. The forms of these updates show that sufficient statistics from each set of variables are passed among each other until convergence to an internally consistent (Bayes optimal) solution. In terms of neuronal implementation, this might be likened to the exchange of neuronal signals via extrinsic connections among functionally specialised brain systems. In this schematic, we have associated perception (inference about the current state of the world) with the prefrontal cortex, while assigning action selection to the basal ganglia. Crucially, precision has been associated with dopaminergic projections from ventral tegmental area and substantia nigra that, necessarily, project to both cortical (perceptual) and subcortical (action selection) systems. See (Friston et al., 2013) for further details. The precise form of this model, and the anatomical mappings implied in the figure, are not mean to be definitive, but we present them to illustrate the underlying plausibility of our simple scheme.