Both high mood and the emotion of pleasure are symbolic messages from the CNS to the conscious mind that the state of the organism is good and that the directions in which behavior is taking the organism are positive, in terms of fitness. Thus, they can be seen as symbolic media facilitating the integrity and functioning of the organism as an adaptive system, again in terms of fitness. The fitness functions of pleasure and other emotions lie in the way they put together and allow a complex organism with a CNS to confront an environment. Many somatic systems, perhaps thousands, integrate and send a message to higher levels of the CNS produce emotion. The communicative function of emotion has fitness value by itself.
Emotions are among the least behaviorally and perceptually linked psychological processes.
They are regulators of the entire nervous system. For example, pleasure encapsulates the essence of survival and adaptation. The internal approach has the advantage of generating more neurophysiological hypotheses. Chemicals that diffuse through relatively large ares of the brain are often linked with emotions. One can look at the structure of communication created by evolution on many levels.