The epithalamus is a posterior (dorsal) segment of the

diencephalon The diencephalon (or interbrain) is a division of the forebrain (embryonic ''prosencephalon''). It is situated between the telencephalon and the midbrain (embryonic ''mesencephalon''). The diencephalon has also been known as the 'tweenbrain in ol ...

. The epithalamus includes the

habenular nuclei In neuroanatomy, habenula (diminutive of Latin ''habena'' meaning rein) originally denoted the stalk of the pineal gland (pineal habenula; pedunculus of pineal body), but gradually came to refer to a neighboring group of nerve cells with which th ...

and their interconnecting fibers, the

habenular commissure The habenular commissure, is a brain commissure (a band of nerve fibers) situated in front of the pineal gland that connects the habenular nuclei on both sides of the diencephalon. The habenular commissure is part of the habenular trigone (a smal ...

, the

stria medullaris The stria medullaris is a part of the epithalamus. It is a fiber bundle containing afferent fibers from the septal nuclei, lateral preoptico-hypothalamic region, and anterior thalamic nuclei to the habenula. It forms a horizontal ridge on the medi ...

and the

pineal gland The pineal gland, conarium, or epiphysis cerebri, is a small endocrine gland in the brain of most vertebrates. The pineal gland produces melatonin, a serotonin-derived hormone which modulates sleep, sleep patterns in both circadian rhythm, circ ...

Functions

The function of the epithalamus is to connect the

limbic system The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the forebrain.Schacter, Daniel L. 2012. ''Ps ...

to other parts of the brain. The epithalamus also serves as a connecting point for the dorsal diencephalic conduction system, which is responsible for carrying information from the limbic forebrain to limbic midbrain structures. Some functions of its components include the secretion of melatonin and secretion of hormones from the pituitary gland (by the

circadian rhythm A circadian rhythm (), or circadian cycle, is a natural, internal process that regulates the sleep–wake cycle and repeats roughly every 24 hours. It can refer to any process that originates within an organism (i.e., Endogeny (biology), endogeno ...

s), regulation of motor pathways and

emotion Emotions are mental states brought on by neurophysiological changes, variously associated with thoughts, feelings, behavioral responses, and a degree of pleasure or displeasure. There is currently no scientific consensus on a definition. ...

s, and how energy is conserved in the body. A study has shown that the lateral habenula, an epithalamic structure, produces spontaneous theta oscillatory activity that was correlated with theta oscillation in the hippocampus. The same study also found that the increase in theta waves in both lateral habenula and hippocampus was correlated with increased memory performance in rats. This suggests that the lateral habenula has an interaction with the hippocampus that is involved in hippocampus-dependent spatial information processing.

Components

The epithalamus is a tiny structure that comprises the

habenular trigone In neuroanatomy, habenula (diminutive of Latin ''habena'' meaning rein) originally denoted the stalk of the pineal gland (pineal habenula; pedunculus of pineal body), but gradually came to refer to a neighboring group of nerve cells with which th ...

, the

, and the

. It is wired with the limbic system and

basal ganglia The basal ganglia (BG), or basal nuclei, are a group of subcortical nuclei, of varied origin, in the brains of vertebrates. In humans, and some primates, there are some differences, mainly in the division of the globus pallidus into an extern ...

. Species that possess a photoreceptive parapineal organ show asymmetry in the epithalamus at the habenula, to the left (dorsal).

Clinical significance

Dysfunction of the epithalamus can be related to mood disorders (such as major depression),

schizophrenia Schizophrenia is a mental disorder characterized by continuous or relapsing episodes of psychosis. Major symptoms include hallucinations (typically hearing voices), delusions, and disorganized thinking. Other symptoms include social withdra ...

, and sleeping disorders. Low levels of melatonin will typically give rise to mood disorders.

Calcification Calcification is the accumulation of calcium salts in a body tissue. It normally occurs in the formation of bone, but calcium can be deposited abnormally in soft tissue,Miller, J. D. Cardiovascular calcification: Orbicular origins. ''Nature Mat ...

of the epithalamus can be linked to periventricular lesions near the limbic system, and lesions of cortico-subcortical pathways that are involved with schizophrenia.

Sleep disorders

The epithalamus is associated with sleep disorders like insomnia revolving around circadian rhythms of sleep wake cycles. The close connection of the epithalamus with the limbic system regulates the secretion of melatonin by the pineal gland and the regulation of motor pathways and emotions. The secretion of melatonin happens in a cycle. Secretion is high at night or in the absence of light and low during the day. The

suprachiasmatic nucleus The suprachiasmatic nucleus or nuclei (SCN) is a tiny region of the brain in the hypothalamus, situated directly above the optic chiasm. It is responsible for controlling circadian rhythms. The neuronal and hormonal activities it generates regula ...

in the hypothalamus is responsible for this cycle of secretion from the epithalamus, specifically from the pineal gland. The Circadian timekeeping is driven in cells by the cyclical activity of core clock genes and proteins such as per2/PER2. Gamma-aminobutyric acid and several peptide factors, including cytokines, growth hormone-releasing hormone and prolactin, are related to sleep promotion.

References

External links

https://web.archive.org/web/20080504165606/http://isc.temple.edu/neuroanatomy/lab/atlas/pdhn/

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