Getting to the bottom of feeding behaviour: who's on top?

Traditionally there has been a tendency to focus on peripheral "bottom-up" feeding-related signals and their resulting downstream actions on hypothalamic centers when studying the feeding behaviour of animals. A problem with this hierarchal approach emerges especially with respect to acquiring a human model attempting to explain what is ultimately a distributed control of feeding and energy balance. This review focuses on illuminating the means by which we have come to understand the complexities of feeding, and takes the next step in an attempt to propose a distinctive top-down view of this composite behaviour. It is argued that in evolutionary terms humans demonstrate behaviours unique to all species as represented by an expanded forebrain and the resultant psychological "non-homeostatic" mediators of feeding. Emphasis is placed on a distributionist "two-tier" model, arguing that traditional short-term (cholescystokinin, ghrelin, peptide YY, glucagon-like peptide 1, etc.) and long-term (insulin and leptin) feeding signals may be actively suppressed by the nested nuclei and projections of cortical-limbic brain areas. It is the motivational state (dependent on depletion-repletion signals of hunger and satiety) that in turn has the capability to modulate how rewarding or how palatable a food item may be perceived; thus, both sides of the two-tiered model of feeding behaviour are complimentary and interdependent all at once. In the end, this paper is both commentary and critical review. This synthesis purports that as evolutionary processes spawned consciousness, the psychology of hunger and the present-day discordance of gene-environment interaction forever changed the feeding behaviour of Homo sapiens.