An animal’s brain monitors energy in the environment and within the body and then adjusts eating behavior, energy utilization, and fat stores to maintain a balance. This chapter will discuss how the brain performs this life-giving task. The brain integrates energy-related sensory information from the eyes, ears, nose, tongue, gastrointestinal tract, liver, pancreas, and blood. In many parts of the body and brain, there are specialized receptors to detect nutrient-rich molecules. The hypothalamus is one of the areas that use this information to adjust physiological functions for storing or utilizing energy at appropriate times. The hypothalamus also contributes to the control of food intake by interacting with mechanisms for voluntary behavior that are essential for obtaining food. This physiological and behavioral control involves connections to the pituitary for endocrine regulation and feedback actions of hormones impacting on the brain. It also involves connections to the hindbrain, which subserve essential feeding reﬂexes and gut responses. The whole system is integrated by circuits extending to forebrain systems for choosing, instigating and reinforcing food choices. These circuits allow the brain to adjust its physiology and behavior to meet the economic demands of the ecological niche in
which the animal lives. This introductory section brieﬂy summarizes the diﬀerent hormones, neurochemicals and brain areas that are required to perform these functions. These are listed in Table 1, together with the abbreviations used in the sections below.