<P> Prior to consuming a meal, the body's energy reserves are in reasonable homeostatic balance . However, when a meal is consumed, there is a homeostasis - disturbing influx of fuels into the bloodstream . When the usual mealtime approaches, the body takes steps to soften the impact of the homeostasis - disturbing influx of fuels by releasing insulin into the blood, and lowering the blood glucose levels . It is this lowering of blood glucose levels that causes premeal hunger, and not necessarily an energy deficit . </P> <P> Hunger appears to increase activity and movement in many animals--for example, an experiment on spiders showed increased activity and predation in starved spiders, resulting in larger weight gain . This pattern is seen in many animals, including humans while sleeping . It even occurs in rats with their cerebral cortex or stomachs completely removed . Increased activity on hamster wheels occurred when rats were deprived not only of food, but also water or B vitamins such as thiamine . This response may increase the animal's chance of finding food, though it has also been speculated the reaction relieves pressure on the home population . There is also a difference between the neurological responses in human males and females in response to hunger and satiety . </P> <P> A food craving is an intense desire to consume a specific food, as opposed to general hunger . Similarly, thirst is the craving for water . </P>

The area in the brain that reduced hunger when it is activated is the