Letâs take a look at the diencephalon in a midsagittal view. The diencephalon makes up the central core of the brain. Itâs made up of three regions: the thalamus, which is the central region, filters information ascending to the cerebral cortex. The hypothalamus, which monitors various conditions in the body, plays an important role in homeostasis. The hypothalamus contains the mammillary body. The pituitary gland is attached to the hypothalamus by a stalk called the infundibulum. and the epithalamus which contains the Pineal body, a gland that secretes the hormone Melatonin.