²⁰Reducing uncertainty as measured by entropy can even be seen as a general learning principle for the brain (Friston, 2010), and thus failure to reduce uncertainty should generate an error signal. At the same time, reducing uncertainty, unpredictability, and uncontrollability is very closely related to the goal of curiosity. Uncertainty can be reduced by a curious investigation of new aspects of the environment, and uncontrollability can be reduced by trying out the effects of actions in new circumstances.