The part of the brain most closely associated with the regulation of hunger, thirst and body temperature is the :

Hypothalamus is the part of the brain that is most closely associated with regulation of hunger, thirst, and the body temperature. Hypothalamus is a small but an important part of the brain below the thalamus; it contains several small nuclei with a variety of functions. It plays important roles in the nervous system as well as in the endocrine system.  Hypothalamus is linked to pituitary gland which is also a vital gland in the endocrine system.