Abstract
This article reviewed the free-energy principle, proposed as the general and unified brain theory by Friston, K. et al. (2006), its powerful framework, and recent expansions. This theory developed a mathematically precise theory to explain the computational neural mechanisms for optimizing posterior beliefs of the world in the brain. The freeenergy principle consisted of two major inferences: the unconscious inference and active inference. In addition, to optimize posterior beliefs or to select and execute behaviors, this theory proposed the precision of signals and its optimization as important computations; it also predicted the aberrant optimization of precision triggered various psychopathological syndromes. Furthermore, the free-energy principle theoretically demonstrated the composition of values from intrinsic (or epistemic) and extrinsic values. Intrinsic values were considered to involve curiosity and play fundamental roles in decision making and behavioral selection. This article expounded how the free-energy principle gave the theoretical explanations for brain functions such as perception, motor behavior, behavioral selection, and insight.
