There is increasing focus on the neurophysiological underpinnings of brain activations, giving birth to an emerging branch of neuroscience--neuroenergetics. However, no common definition of "brain activation" exists thus far. In this article, we define brain activation as the information-driven reorganization of energy flows in a population of neuroglial units that leads to an overall increase in energy utilization in this population. On the basis of this definition, the key aspects of modern biochemical and biophysical approaches to neuroenergetics are considered from the perspective of the links between these approaches within the context of the free energy minimization principle and the neurophysiological conception of deviance detection. In this light, we consider brain basal activity as subserving internal representations of the environment (predictive coding), and brain activation as reflecting the level of deviance from predictive coding. (Contains 3 figures.)