The diencephalon is the caudal part of the forebrain (prosencephalon), located between the midbrain (mesencephalon) and the cerebrum (telencephalon). It consists of the thalamus, hypothalamus, epithalamus, and subthalamus. The thalamus is the relay center for sensory information. The hypothalamus regulates autonomic function and the endocrine system. The epithalamus, which comprises the pineal gland, habenula, habenular commissure, and stria medullaris, regulates the sleep-wake cycle. The subthalamus, which contains the subthalamic nucleus, is part of the indirect basal ganglia circuit and is involved in the inhibition of involuntary movements. The limbic system consists of the amygdala, hypothalamus, anterior thalamus, hippocampus, mammillary bodies, cingulate cortex, and entorhinal cortex. These structures are involved in memory formation, regulation of appetite and satiety, attention, emotional responses, and sexual arousal.
- Location: caudal portion of the forebrain, situated between the cerebrum and midbrain
- Embryogenesis: arises from prosencephalon
- Composition and function
- Location: dorsal part of diencephalon, located above the midbrain
- Function: a group of nuclei constituting the main relay center of ascending sensory information between subcortical and cortical (except for the sense of smell)
|Overview of thalamic nuclei|
|Anterior nuclear group|
|Anterior thalamic nuclei|
|Lateral nuclear group|
|Lateral dorsal thalamic nucleus|| |
|Posterior subgroup||Pulvinar|| || |
|Lateral posterior thalamic nucleus|| |
|Ventral anterior thalamic nucleus|| |
|Ventral lateral thalamic nucleus|| |
|Ventral posterior thalamic nucleus||Ventral posterolateral thalamic nucleus (VPL)|
|Ventral posteromedial thalamic nucleus (VPM)|| || |
|Medial nuclear group|
|Dorsomedial thalamic nucleus|| |
|Lateral geniculate thalamic nucleus|| |
|Medial geniculate thalamic nucleus|| |
|Intralaminar nuclear group|
|Intralaminar thalamic nuclei|| |
VPL: receives sensory information from the Limbs. VPM: receives sensory information from your Mug (face).
The Lateral geniculate body processes Light (part of the visual pathway); the Medial geniculate body processes Music (part of the hearing pathway).
Blood supply 
Mainly derived from branches of the (P1 and P2 segments):
- Posterior thalamosubthalamic paramedian arteries
- Thalamogeniculate arteries
- Posterior choroidal arteries
- Branches of the :
- For more information on the clinical significance of infarction of the thalamus, see “ ” in “ .”
- Location: anterior part of the diencephalon, ventral and inferior to the thalamus
- Control center for the autonomic nervous system
- Regulates hormonal pathways and autonomic functions
- Production of hypothalamic hormones that (e.g., GHRH, somatostatin, dopamine) mostly affect the hormonal secretion of the anterior pituitary gland
- For more information on the function of the hypothalamus, see “ ” in “ ”
- Composition: four nuclear groups
|Overview of hypothalamic nuclei|
|Nucleus||Function||Clinical significance of injury|
|Supraoptic (anterior) nuclear group|
|Anterior hypothalamic nucleus|| || |
|Preoptic nucleus|| |
|Tuberal (middle) nuclear group|
|Dorsomedial hypothalamic nucleus|| |
|Ventromedial hypothalamic nucleus|| || |
|Arcuate hypothalamic nucleus|| |
|Mammillary (posterior) nuclear group|
|Posterior hypothalamic nucleus|| || |
|Preoptic (anterior-posterior) nuclear group|
Hypothalamic functions (Thirst and water balance; Adenohypophysis produces releasing hormones that act on the anterior pituitary, Neurohypophysis produces ADH and oxytocin for the posterior pituitary; Hunger; Anger; Temperature; Sexual functions): TAN HATS
The MaMmillary bOdY is important for MeMOrY.
Epithalamus and Subthalamus
- Location: dorsal diencephalon, superior and posterior to thalamus
- Composition: habenula, habenular commissure, stria medullaris, and pineal gland
- Blood supply: posterior cerebral artery → posterior choroidal arteries
|Overview of the epithalamus|
|Pineal gland|| |
|Habenular commissure|| || || |
|Stria medullaris|| |
- Location: lateral to the hypothalamus, rostral to the thalamus, and medial to the internal capsule
- Function: part of the circuitry, involved in the modulation motor function
- The is the most prominent structure.
- The subthalamic nucleus has excitatory glutamatergic projections to both segments of the and
- Clinical relevance: A lesion of the subthalamic nucleus can lead to contralateral .
- For more information on the subthalamus, see “ ” in “ .”
- Function: involved in emotional and behavioral responses, motivation, memory, olfaction, and autonomic nervous system function
- Areas of the cerebral cortex: hippocampal formation (hippocampus, dentate gyrus, entorhinal cortex), cingulate gyrus
- Nuclei: mammillary bodies, amygdala, anterior thalamic nuclei
- Nerve fiber tracts
Components of the limbic system
|Overview of the limbic system|
|Mammillary bodies|| |
|Cingulate gyrus|| |
Circuit: pyramidal cells of the hippocampus → fornix → mammillary bodies (hypothalamus) → mammillothalamic tract → anterior thalamic nucleus → anterior limb of the internal capsule → cingulate gyrus → cingulum → entorhinal cortex → hippocampus
- The hippocampus receives input from cortical associations such as the cingulum, cingulate gyrus, and parahippocampal gyrus.
- The hippocampus receives input from and sends output to the amygdala.
- The amygdala is involved in emotional regulation and encoding of emotionally influenced memory (positive or negative).
The limbic system is responsible for the famous 5 F's: Feeding, Fleeing, Fighting, Feeling, and … Sex.