We eat in order to function and survive. When and how much we eat is largely determined by our metabolism (the rate at which the body uses energy). Several physiological mechanisms try to maintain this energy homeostasis (balance). The main area of the brain involved in the regulation of appetite is the hypothalamus.The hypothalamus regulates a number of important bodily functions, including eating behaviour, two sub-sections of the hypothalamus have been found to be important for this; the lateral hypothalamus (LH) and the ventromedial hypothalamic nucleus (VMH).
The LH has been identified to determine when we are hungry, Stanley (1986) supports the role of the LH as a feeding centre; he found that the neurotransmitter neuropeptide Y (NPY) is important in turning on feeding, when injected into rats NPY causes them to immediately begin eating, even if they are satiated. Repeated injections caused obesity in just a few days. Anad and Brobeck (1951) found that the LH when damaged led to a loss of feeding behaviour and subsequent weight loss. The animal would not know they were hungry (aphagia) and so would not eat.
However, Sakurai (1998) suggests that the LH has many functions not just as an “eating centre”. Damage to the LH causes deficits in thirst and sex drives suggesting the LH may be important in regulating eating behaviour, although its primary function is not simply an eating centre. Furthermore, research has found that lesions to the nigrostriatal tract (NST), a brain structure which passes through the LH produces aphagia (under-eating) and adipsia (under-drinking) on their own. Therefore, it is impossible to say if it is damage to this brain structure or the LH itself which results in loss of feeding behaviour.
The VMH has been identified to determine when we are full; Reeves and Plum (1969) conducted a post-mortem on an obese female, finding that her VMH has been destroyed.