For those of us who refused to be discouraged there remained one slight hope. Buried deep down in the massive human brain there is a part which we have in common with all vertebrate animals the so-called diencephalon. It is a very primitive part of the brain and has in man been almost smothered by the huge masses of nervous tissue with which we think, reason and voluntarily move our body. The diencephalon is the part from which the central nervous system controls all the automatic animal functions of the body, such as breathing, the heart beat, digestion, sleep, sex, the urinary system, the autonomous or vegetative nervous system and via the pituitary the whole interplay of the endocrine glands.
It was therefore not unreasonable to suppose that the complex operation of storing and issuing fuel to the body might also be controlled by the diencephalon. It has long been known that the content of sugar – another form of fuel – in the blood depends on a certain nervous center in the diencephalon. When this center is destroyed in laboratory animals, they develop a condition rather similar to human stable diabetes. It has also long been known that the destruction of another diencephalic center produces a voracious appetite and a rapid gain in weight in animals which never get fat spontaneously.
Source: The Original Manuscript by Dr. Simeons