[Brain as a Dynamical System].

This article aims at understanding the essential dynamical characteristics of the brain by modeling the brain as a simplified dynamical control system. Although the brain is a highly complex system, such a simplified model provides us insights into its essential features. Using a control system model, the first half of this article describes the dynamics of a system comprising the dorsolateral prefrontal cortex and striatum with dopaminergic modulation and argue its relevance to the functions of the brain with schizophrenia. The second half of this article introduces a model-based analysis of molecular imaging data.