The diencephalon, between the telencephalon and midbrain, consists of four major structures: yhalamus, subthalamus, epithalamus, and hypothalamus. The thalamus, the largest and the most prominent siencephalic nucleus, serves as the sensorimotor relay center to screen all sensory and motor information before channeling it to the cerebral cortex. The thalamus is divided into many functionally specific nuclei, and each of these nuclei makes direct anatomic projections to corresponding functional areas of the neocortex. The subthalamus is important in the organization of motor functions and is functionally related to the basal ganglia. The epithalamus, the oldest part of diencephalon, consists of the habenular nucleus and pineal gland. The pineal gland, an endocrine organ, mediates its influence on sex glands and diurnal rhythem. The hypothalamus is a major diencephalic structure for controlling activities of the autonomic and endocrine system.