Perspective on the central control of appetite.

Within the last 10 to 15 years, a number of discoveries have revised the way in which scientists view the role of the brain in the control of food intake (1). One aspect of the brain's influence is often characterized as the control of energy homeostasis. This term accounts for a number of factors arising from experimental studies on molecules and food consumption but seems to stop well short of explaining how brain processes articulate the variety of patterns of human feeding. It should be kept in mind that eating is 100% behavior, and this activity links the internal world of molecules and physiological processes with the external world of physical and cultural systems. It is not always clear the extent to which human eating patterns are a function of physiological or environmental pressure; this is, of course,the subject of extensive experimental study and debate. Because much of the current scientific activity on neural control of feeding is driven by the need to understand (and deal with) the causes of obesity, it will be necessary, at some stage, to reconcile the effects of the physiological mechanism believed to be responsible for eating control in the obese with the actual patterns of eating displayed (eating phenotypes) by obese people. Ultimately, the mechanisms and the behavioral phenotypes must match up. Initially, it is useful to consider which components of energy homeostasis are codified in specific molecular processes and neural pathways and to describe how the integration of diverse signaling systems (the codification) is translated into the expression of behavior and the accompanying subjective sensations.