Why did Walter Rudolf Hess win The Nobel Prize in Physiology or Medicine in 1949?

The Nobel Prize in Physiology or Medicine 1949 was divided equally between Walter Rudolf Hess for his discovery of the functional organization of the interbrain as a coordinator of the activities of the internal organs and Antonio Caetano de Abreu Freire Egas Moniz for his discovery of the therapeutic value of leucotomy in certain psychoses.