Pain and the brain: specificity and plasticity of the brain in clinical chronic pain.

Descartes proposed that all observable human behavior could be divided into 2 categories, the simple and the complex. Simple behaviors were those in which a given sensation always, deterministically, produced the same behavioral response. . .. Complex behaviors, in contrast were those in which the linkage between sensation and action was unpredictable and subject to the vagaries of volition. . .. They were produced when sensory data were transmitted from the nervous system to the nonmaterial soul, the soul made a decision about what course of action to undertake, and this volitional command was then passed to the machinery of the body for execution. From Paul W. Glimcher, 2003, Decisions, Uncertainty, and the Brain