The diencephalon is the region of the brain that includes the thalamus, metathalamus, hypothalamus, epithalamus, prethalamus or subthalamus and pretectum. The diencephalon and the telencephalon both derive from the prosencephalon.The diencephalon is located near the midline of the brain, above the midbrain.
Thalamus is the largest structure in the diencephalon, the part of the brain situated between the midbrain (mesencephalon) and forebrain (telencephalon).
Hypothalamus is an extremely complex region in the brain of humans, and even small nuclei within the hypothalamus are involved in many different functions.
Epithalamus is a dorsal posterior segment of the diencephalon (a segment in the middle of the brain also containing the hypothalamus and thethalamus) which includes the habenula, the stria medullaris and the pineal body. Its function is the connection between the limbic system to other parts of the brain.
Metathalamus is a composite structure of the thalamus, consisting of the medial geniculate nucleus and the lateral geniculate nucleus.
Prethalamus is patterned by Sonic hedgehog signalling from the ZLI. Anatomically, it develops efferent (output) connections to the striatum (caudate nucleus and putamen) in the telencephalon, to the thalamus (medial and lateral nuclear groups) in the diencephalon, and to the red nucleus and substantia nigra in the mesencephalon. It receives afferent (input) connections from the substantia nigra and striatum.
Pretectum, also known as the pretectal area, is a region of neurons found between the thalamus and midbrain. It receives binocular sensory input from retinal ganglion cells of the eyes, and is the region responsible for maintaining the pupillary light reflex.
