Midbrain

The mesencephalon or midbrain is a part of the brain stem.Mosby’s Medical, nursing and allied health dictionary. 4th ed, Mosby-Year Book 1994. p981 It is associated with vision, hearing, motor control, sleep/wake, arousal (alertness), and temperature regulation.Breedlove, Watson, & Rosenzweig 2010. Biological psychology. 6th ed. 45-46 

In the anatomy of developing animals, the brain forms from the neural tube, which turns into three vesicles. The mesencephalon (midbrain) is the middle vesicle, and becomes part of the brain stem. 

The mesencephalon is ancient in origin, meaning its general architecture is shared with the most ancient of vertebrates. Dopamine produced in the substantia nigra plays a role in motivation and habituation of species from humans to insects.

 References 

Category:Anatomy of the brain