2009 年 42 巻 2 号 p. 2_29-2_40
To survive in changeable circumstances, we have to make appropriate decisions on our behavior. Recent studies have suggested that we have two brain processes to calculate reward values of objects. One is the process coding a specific reward value of a stimulus or event dependent on direct experience. The other enables us to predict reward based on the internal model of given circumstances, including societies, which doesn't necessarily require direct experience. The nigro-striatal network works for the model-free decision and the prefrontal network contributes to the model-based decision. These two networks are cooperative in one occasion and are competitive in another.