The Diencephalon

Abstract The diencephalon (“in-between brain”/interbrain) lies at the central core of the cerebrum, surrounding the third ventricle and surrounded by the cerebral hemispheres (telencephalon). The major structures of the diencephalon are the thalamus, which accounts for about 80% of the diencephalon, and the hypothalamus, which lies inferior to the thalamus. No component of the thalamus is visible from the external surface of the brain, and only a small portion of the hypothalamus is visible from the ventral surface. Both the thalamus and the hypothalamus are composed of multiple nuclei that perform many different functions. This chapter describes basic thalamic anatomy, thalamic nuclei and their functions, thalamic stroke syndromes, basic hypothalamic anatomy, hypothalamic control of lower autonomic and endocrine centers, hypothalamic control of motivated behaviors required for survival and reproduction, and hypothalamic syndromes.