Thalamus
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The thalamus (from
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
θάλαμος, "chamber") is a large mass of
gray matter Grey matter is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses, and capillaries. Grey matter is distingui ...
located in the
dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal c ...
part of the diencephalon (a division of the
forebrain In the anatomy of the brain of vertebrates, the forebrain or prosencephalon is the rostral (forward-most) portion of the brain. The forebrain (prosencephalon), the midbrain (mesencephalon), and hindbrain (rhombencephalon) are the three primary ...
).
Nerve fibers A nerve is an enclosed, cable-like bundle of nerve fibers (called axons) in the peripheral nervous system. A nerve transmits electrical impulses. It is the basic unit of the peripheral nervous system. A nerve provides a common pathway for the e ...
project out of the thalamus to the
cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consistin ...
in all directions, allowing hub-like exchanges of information. It has several functions, such as the relaying of sensory signals, including
motor An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power g ...
signals to the cerebral cortex and the regulation of
consciousness Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
,
sleep Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefulness by a de ...
, and
alertness Alertness is the state of active attention by high sensory awareness such as being watchful and prompt to meet danger or emergency, or being quick to perceive and act. It is related for psychology . A lack of alertness is a symptom of a ...
. Anatomically, it is a paramedian symmetrical structure of two halves (left and right), within the
vertebrate Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...
brain, situated between the cerebral cortex and the
midbrain The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', " ...
. It forms during embryonic development as the main product of the diencephalon, as first recognized by the Swiss embryologist and anatomist Wilhelm His Sr. in 1893.


Anatomy

The thalamus is a paired structure of gray matter located in the
forebrain In the anatomy of the brain of vertebrates, the forebrain or prosencephalon is the rostral (forward-most) portion of the brain. The forebrain (prosencephalon), the midbrain (mesencephalon), and hindbrain (rhombencephalon) are the three primary ...
which is superior to the midbrain, near the center of the brain, with nerve fibers projecting out to the cerebral cortex in all directions. The medial surface of the thalamus constitutes the upper part of the lateral wall of the
third ventricle The third ventricle is one of the four connected ventricles of the ventricular system within the mammalian brain. It is a slit-like cavity formed in the diencephalon between the two thalami, in the midline between the right and left lateral ...
, and is connected to the corresponding surface of the opposite thalamus by a flattened gray band, the
interthalamic adhesion The interthalamic adhesion (also known as the intermediate mass or middle commissure) is a flattened band of tissue that connects both parts of the thalamus at their medial surfaces. The medial surfaces form the upper part of the lateral wall to t ...
. The lateral part of the thalamus is the phylogenetically newest part of the thalamus (neothalamus), and includes the lateral nuclei, the pulvinar and the medial and lateral geniculate nuclei. There are areas of
white matter White matter refers to areas of the central nervous system (CNS) that are mainly made up of myelinated axons, also called tracts. Long thought to be passive tissue, white matter affects learning and brain functions, modulating the distributi ...
in the thalamus including the stratum zonale that covers the dorsal surface, and the external and internal medullary laminae. The external lamina covers the lateral surface and the internal lamina divides the nuclei into anterior, medial and lateral groups.


Blood supply

The thalamus derives its blood supply from a number of arteries: the polar artery (
posterior communicating artery In human anatomy, the left and right posterior communicating arteries are arteries at the base of the brain that form part of the circle of Willis. Each posterior communicating artery connects the three cerebral arteries of the same side. Anterior ...
), paramedian thalamic-subthalamic arteries, inferolateral (thalamogeniculate) arteries, and posterior (medial and lateral) choroidal arteries. These are all branches of the
posterior cerebral artery The posterior cerebral artery (PCA) is one of a pair of cerebral arteries that supply oxygenated blood to the occipital lobe, part of the back of the human brain. The two arteries originate from the distal end of the basilar artery, where it bifur ...
. Some people have the artery of Percheron, which is a rare anatomic variation in which a single arterial trunk arises from the posterior cerebral artery to supply both parts of the thalamus.


Thalamic nuclei

Derivatives of the diencephalon include the dorsally-located
epithalamus The epithalamus is a posterior (dorsal) segment of the diencephalon. The epithalamus includes the habenular nuclei and their interconnecting fibers, the habenular commissure, the stria medullaris and the pineal gland. Functions The function ...
(essentially the
habenula 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 the ...
and annexes) and the perithalamus (prethalamus) containing the
zona incerta The zona incerta (ZI) is a horizontally elongated region of gray matter in the subthalamus below the thalamus. Its connections project extensively over the brain from the cerebral cortex down into the spinal cord. Its function is unknown, though ...
and the
thalamic reticular nucleus The thalamic reticular nucleus is part of the ventral thalamus that forms a capsule around the thalamus laterally. However, recent evidence from mice and fish question this statement and define it as a dorsal thalamic structure. It is separated fro ...
. Due to their different
ontogenetic Ontogeny (also ontogenesis) is the origination and development of an organism (both physical and psychological, e.g., moral development), usually from the time of fertilization of the egg to adult. The term can also be used to refer to the st ...
origins, the epithalamus and the perithalamus are formally distinguished from the thalamus proper. The metathalamus is made up of the lateral geniculate and medial geniculate nuclei. The thalamus comprises a system of
lamellae Lamella (plural lamellae) means a small plate or flake in Latin, and in English may refer to: Biology * Lamella (mycology), a papery rib beneath a mushroom cap * Lamella (botany) * Lamella (surface anatomy), a plate-like structure in an animal * ...
(made up of
myelin Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can be ...
ated fibers) separating different thalamic subparts. Other areas are defined by distinct clusters of
neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...
s, such as the
periventricular nucleus The periventricular nucleus is a thin sheet of small neurons located in the wall of the third ventricle, a composite structure of the hypothalamus. It functions in analgesia. It is located in the rostral, intermediate, and caudal regions of t ...
, the intralaminar elements, the "nucleus limitans", and others. These latter structures, different in structure from the major part of the thalamus, have been grouped together into the ''
allothalamus The Allothalamus is a division used by some researchers in describing the thalamus. Paramedian formation This or periventricular formation lies along the wall of the third ventricle. In man where there is no or almost no adhaesio interthalamica ...
'' as opposed to the ''
isothalamus The isothalamus is a division used by some researchers in describing the thalamus. The isothalamus constitutes 90% or more of the thalamus, and despite the variety of functions it serves, follows a simple organizational scheme. The constituting ...
''. This distinction simplifies the global description of the thalamus.


Connections

The thalamus has many connections to the hippocampus via the
mammillothalamic tract The mammillothalamic tract (mammillothalamic fasciculus, thalamomammillary fasciculus, bundle of Vicq d’Azyr) arises from cells in both the medial and lateral nuclei of the mammillary body and by fibers that are directly continued from the for ...
, this tract comprises the
mammillary bodies The mammillary bodies are a pair of small round bodies, located on the undersurface of the brain that, as part of the diencephalon, form part of the limbic system. They are located at the ends of the anterior arches of the fornix. They consist o ...
and fornix. The thalamus is connected to the
cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consistin ...
via the
thalamocortical radiations In neuroanatomy, thalamocortical radiations are the fibers between the thalamus and the cerebral cortex. Structure Thalamocortical (TC) fibers have been referred to as one of the two constituents of the isothalamus, the other being micro neurons ...
. The
spinothalamic tract The spinothalamic tract is a part of the anterolateral system or the ventrolateral system, a sensory pathway to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upward to the somatosensory co ...
is a sensory pathway originating in the spinal cord. It transmits information to the thalamus about pain, temperature, itch and
crude touch In physiology, the somatosensory system is the network of neural structures in the brain and body that produce the perception of touch (haptic perception), as well as temperature (thermoception), body position (proprioception), and pain. It i ...
. There are two main parts: the
lateral spinothalamic tract The spinothalamic tract is a part of the anterolateral system or the ventrolateral system, a sensory pathway to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upward to the somatosensory cor ...
, which transmits pain and temperature, and the anterior (or ventral) spinothalamic tract, which transmits crude touch and pressure.


Function

The thalamus has multiple functions, generally believed to act as a relay station, or hub, relaying information between different subcortical areas and the cerebral cortex. In particular, every sensory system (with the exception of the
olfactory system The olfactory system, or sense of smell, is the sensory system used for smelling ( olfaction). Olfaction is one of the special senses, that have directly associated specific organs. Most mammals and reptiles have a main olfactory system and an ...
) includes a thalamic nucleus that receives sensory signals and sends them to the associated primary cortical area. For the visual system, for example, inputs from the
retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then ...
are sent to the
lateral geniculate nucleus In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, ventral projec ...
of the thalamus, which in turn projects to the
visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus and ...
in the
occipital lobe The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin ''ob'', "behind", and ''caput'', "head". The occipital lobe is the vi ...
. The thalamus is believed to both process sensory information as well as relay it—each of the primary sensory relay areas receives strong feedback connections from the cerebral cortex. Similarly the
medial geniculate nucleus The medial geniculate nucleus (MGN) or medial geniculate body (MGB) is part of the auditory thalamus and represents the thalamic relay between the inferior colliculus (IC) and the auditory cortex (AC). It is made up of a number of sub-nuclei that ...
acts as a key auditory relay between the
inferior colliculus The inferior colliculus (IC) (Latin for ''lower hill'') is the principal midbrain nucleus of the auditory pathway and receives input from several peripheral brainstem nuclei in the auditory pathway, as well as inputs from the auditory cortex. T ...
of the
midbrain The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', " ...
and the
primary auditory cortex The auditory cortex is the part of the temporal lobe that processes auditory information in humans and many other vertebrates. It is a part of the auditory system, performing basic and higher functions in hearing, such as possible relations to ...
. The
ventral posterior nucleus The ventral posterior nucleus is the somato-sensory relay nucleus in thalamus of the brain. Input and output The ventral posterior nucleus receives neuronal input from the medial lemniscus, spinothalamic tracts, and trigeminothalamic tract. It p ...
is a key
somatosensory In physiology, the somatosensory system is the network of neural structures in the brain and body that produce the perception of touch (haptic perception), as well as temperature (thermoception), body position (proprioception), and pain. It i ...
relay, which sends touch and
proprioceptive Proprioception ( ), also referred to as kinaesthesia (or kinesthesia), is the sense of self-movement, force, and body position. It is sometimes described as the "sixth sense". Proprioception is mediated by proprioceptors, mechanosensory neurons ...
information to the
primary somatosensory cortex In neuroanatomy, the primary somatosensory cortex is located in the postcentral gyrus of the Human brain, brain's parietal lobe, and is part of the somatosensory system. It was initially defined from surface stimulation studies of Wilder Penfield ...
. The thalamus also plays an important role in regulating states of sleep and wakefulness. Thalamic nuclei have strong reciprocal connections with the cerebral cortex, forming
thalamo-cortico-thalamic circuits Thalamo-cortico-thalamic circuits consist of looped neural pathways that connect the thalamus to the cerebral cortex, and connect the cerebral cortex back to the thalamus. Some researchers propose that such circuits allow the brain to obtain data on ...
that are believed to be involved with
consciousness Consciousness, at its simplest, is sentience and awareness of internal and external existence. However, the lack of definitions has led to millennia of analyses, explanations and debates by philosophers, theologians, linguisticians, and scien ...
. The thalamus plays a major role in regulating arousal, the level of awareness, and activity. Damage to the thalamus can lead to permanent coma. The role of the thalamus in the more anterior
pallidal The globus pallidus (GP), also known as paleostriatum or dorsal pallidum, is a subcortical structure of the brain. It consists of two adjacent segments, one external, known in rodents simply as the globus pallidus, and one internal, known in rode ...
and
nigral The substantia nigra (SN) is a basal ganglia structure located in the midbrain that plays an important role in reward and movement. ''Substantia nigra'' is Latin for "black substance", reflecting the fact that parts of the substantia nigra app ...
territories in the
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 ...
system disturbances is recognized but still poorly understood. The contribution of the thalamus to vestibular or to
tectal The midbrain or mesencephalon is the forward-most portion of the brainstem and is associated with vision, hearing, motor control, sleep and wakefulness, arousal (alertness), and temperature regulation. The name comes from the Greek ''mesos'', "m ...
functions is almost ignored. The thalamus has been thought of as a "relay" that simply forwards signals to the cerebral cortex. Newer research suggests that thalamic function is more selective. Many different functions are linked to various regions of the thalamus. This is the case for many of the sensory systems (except for the olfactory system), such as the auditory, somatic,
visceral In biology, an organ is a collection of tissues joined in a structural unit to serve a common function. In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells to act together in a ...
,
gustatory The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ...
and
visual system The visual system comprises the sensory organ (the eye) and parts of the central nervous system (the retina containing photoreceptor cells, the optic nerve, the optic tract and the visual cortex) which gives organisms the sense of sight (th ...
s where localized lesions provoke specific sensory deficits. A major role of the thalamus is support of motor and language systems, and much of the circuitry implicated for these systems is shared. The thalamus is ''functionally connected'' to the
hippocampus The hippocampus (via Latin from Greek , 'seahorse') is a major component of the brain of humans and other vertebrates. Humans and other mammals have two hippocampi, one in each side of the brain. The hippocampus is part of the limbic system, a ...
as part of the extended hippocampal system at the thalamic anterior nuclei with respect to spatial memory and spatial sensory datum they are crucial for human episodic event memory. The thalamic region's connection to the mesio-temporal lobe provide differentiation of the functioning of recollective and familiarity memory. The neuronal information processes necessary for motor control were proposed as a network involving the thalamus as a subcortical motor center. Through investigations of the anatomy of the brains of primates the nature of the interconnected tissues of the
cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebel ...
to the multiple motor cortices suggested that the thalamus fulfills a key function in providing the specific channels from the basal ganglia and cerebellum to the cortical motor areas. In an investigation of the
saccade A saccade ( , French for ''jerk'') is a quick, simultaneous movement of both eyes between two or more phases of fixation in the same direction.Cassin, B. and Solomon, S. ''Dictionary of Eye Terminology''. Gainesville, Florida: Triad Publishi ...
and antisaccade motor response in three monkeys, the thalamic regions were found to be involved in the generation of antisaccade eye-movement (that is, the ability to inhibit the reflexive jerking movement of the eyes in the direction of a presented stimulus). Recent research suggests that the mediodorsal thalamus (MD) may play a broader role in cognition. Specifically, the mediodorsal thalamus may "amplify the connectivity (signaling strength) of just the circuits in the cortex appropriate for the current context and thereby contribute to the flexibility (of the mammalian brain) to make complex decisions by wiring the many associations on which decisions depend into weakly connected cortical circuits." Researchers found that "enhancing MD activity magnified the ability of mice to "think," driving down by more than 25 percent their error rate in deciding which conflicting sensory stimuli to follow to find the reward."


Development

The thalamic complex is composed of the perithalamus (or prethalamus, previously also known as ventral thalamus), the mid-diencephalic organiser (which forms later the
zona limitans intrathalamica The ''zona limitans intrathalamica'' (ZLI) is a lineage-restriction compartment and primary developmental boundary in the vertebrate forebrain (which is analogous to the human cerebrum) that serves as a signaling center and a restrictive border bet ...
(ZLI) ) and the thalamus (dorsal thalamus). The development of the thalamus can be subdivided into three steps. The thalamus is the largest structure deriving from the embryonic diencephalon, the posterior part of the forebrain situated between the midbrain and the cerebrum.


Early brain development

After neurulation the anlage of the
prethalamus The subthalamus or prethalamus is a part of the diencephalon. Its most prominent structure is the subthalamic nucleus. The subthalamus connects to the globus pallidus, a basal nucleus of the telencephalon. Structure The subthalamus is located ...
and the thalamus is induced within the neural tube. Data from different vertebrate model organisms support a model in which the interaction between two
transcription factor In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fu ...
s, Fez and Otx, are of decisive importance. Fez is expressed in the prethalamus, and functional experiments show that Fez is required for prethalamus formation. Posteriorly, Otx1 and Otx2 abut the expression domain of Fez and are required for proper development of the thalamus.


Formation of progenitor domains

Early in thalamic development two progenitor domains form, a caudal domain, and a rostral domain. The caudal domain gives rise to all of the glutamatergic neurons in the adult thalamus while the rostral domain gives rise to all of the GABAergic neurons in the adult thalamus.


The formation of the mid-diencephalic organiser (MDO)

At the interface between the expression domains of Fez and Otx, the mid-diencephalic organizer (MDO, also called the ZLI organiser) is induced within the thalamic anlage. The MDO is the central signalling organizer in the thalamus. A lack of the organizer leads to the absence of the thalamus. The MDO matures from ventral to dorsal during development. Members of the sonic hedgehog (SHH) family and of the Wnt family are the main principal signals emitted by the MDO. Besides its importance as signalling center, the organizer matures into the morphological structure of the
zona limitans intrathalamica The ''zona limitans intrathalamica'' (ZLI) is a lineage-restriction compartment and primary developmental boundary in the vertebrate forebrain (which is analogous to the human cerebrum) that serves as a signaling center and a restrictive border bet ...
(ZLI).


Maturation and parcellation of the thalamus

After its induction, the MDO starts to orchestrate the development of the thalamic anlage by release of signalling molecules such as SHH. In mice, the function of signaling at the MDO has not been addressed directly due to a complete absence of the diencephalon in SHH mutants. Studies in chicks have shown that SHH is both necessary and sufficient for thalamic gene induction. In
zebrafish The zebrafish (''Danio rerio'') is a freshwater fish belonging to the minnow family (Cyprinidae) of the order Cypriniformes. Native to South Asia, it is a popular aquarium fish, frequently sold under the trade name zebra danio (and thus often ca ...
, it was shown that the expression of two SHH genes, SHH-a and SHH-b (formerly described as twhh) mark the MDO territory, and that SHH signaling is sufficient for the molecular differentiation of both the prethalamus and the thalamus but is not required for their maintenance and SHH signaling from the MDO/alar plate is sufficient for the maturation of prethalamic and thalamic territory while ventral Shh signals are dispensable. The exposure to SHH leads to differentiation of thalamic neurons. SHH signaling from the MDO induces a posterior-to-anterior wave of expression the proneural gene Neurogenin1 in the major (caudal) part of the thalamus, and Ascl1 (formerly Mash1) in the remaining narrow stripe of rostral thalamic cells immediately adjacent to the MDO, and in the prethalamus. This zonation of proneural gene expression leads to the differentiation of glutamatergic relay neurons from the Neurogenin1+ precursors and of GABAergic inhibitory neurons from the Ascl1+ precursors. In fish, selection of these alternative neurotransmitter fates is controlled by the dynamic expression of Her6 the homolog of
HES1 Transcription factor HES1 (hairy and enhancer of split-1) is a protein that is encoded by the ''Hes1'' gene, and is the mammalian homolog of the hairy gene in ''Drosophila.'' HES1 is one of the seven members of the Hes gene family (HES1-7). Hes ge ...
. Expression of this hairy-like bHLH
transcription factor In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fu ...
, which represses Neurogenin but is required for Ascl1, is progressively lost from the caudal thalamus but maintained in the prethalamus and in the stripe of rostral thalamic cells. In addition, studies on chick and mice have shown that blocking the Shh pathway leads to absence of the rostral thalamus and substantial decrease of the caudal thalamus. The rostral thalamus will give rise to the reticular nucleus mainly whereby the caudal thalamus will form the relay thalamus and will be further subdivided in the
thalamic nuclei This traditional list does not accord strictly with human thalamic anatomy. Nuclear groups of the thalamus include: *anterior nuclear group ** anteroventral nucleus ** anterodorsal nucleus ** anteromedial nucleus **superficial ("lateral dorsal" ...
. In humans, a common genetic variation in the promoter region of the
serotonin transporter The serotonin transporter (SERT or 5-HTT) also known as the sodium-dependent serotonin transporter and solute carrier family 6 member 4 is a protein that in humans is encoded by the SLC6A4 gene. SERT is a type of monoamine transporter protein tha ...
(the SERT-long and -short allele: 5-HTTLPR) has been shown to affect the development of several regions of the thalamus in adults. People who inherit two short
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...
s (SERT-ss) have more neurons and a larger volume in the pulvinar and possibly the limbic regions of the thalamus. Enlargement of the thalamus provides an anatomical basis for why people who inherit two SERT-ss alleles are more vulnerable to
major depression Major depressive disorder (MDD), also known as clinical depression, is a mental disorder characterized by at least two weeks of pervasive low mood, low self-esteem, and loss of interest or pleasure in normally enjoyable activities. Introdu ...
,
post-traumatic stress disorder Post-traumatic stress disorder (PTSD) is a mental and behavioral disorder that can develop because of exposure to a traumatic event, such as sexual assault, warfare, traffic collisions, child abuse, domestic violence, or other threats on ...
, and suicide.


Clinical significance

A thalamus damaged by a stroke can lead to
thalamic pain syndrome The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all direction ...
, which involves a one-sided burning or aching sensation often accompanied by
mood swings A mood swing is an extreme or sudden change of mood. Such changes can play a positive part in promoting problem solving and in producing flexible forward planning, or be disruptive. When mood swings are severe, they may be categorized as par ...
. Bilateral ischemia of the area supplied by the paramedian artery can cause serious problems including
akinetic mutism Akinetic mutism is a medical term describing patients tending neither to move (akinesia) nor speak (mutism). Akinetic mutism was first described in 1941 as a mental state where patients lack the ability to move or speak. However, their eyes may fo ...
, and be accompanied by
oculomotor The oculomotor nerve, also known as the third cranial nerve, cranial nerve III, or simply CN III, is a cranial nerve that enters the orbit (anatomy), orbit through the superior orbital fissure and innervates extraocular muscles that enable mo ...
problems. A related concept is
thalamocortical dysrhythmia Thalamocortical dysrhythmia (TCD) is a theoretical framework in which neuroscientists try to explain the positive and negative symptoms induced by neuropsychiatric disorders like Parkinson's Disease, neurogenic pain, tinnitus, visual snow syndrom ...
. The occlusion of the artery of Percheron can lead to a bilateral thalamus infarction.
Alcoholic Korsakoff syndrome Korsakoff syndrome (KS) is a disorder of the central nervous system characterized by amnesia, deficits in explicit memory, and confabulation. This neurological disorder is caused by a deficiency of thiamine (vitamin B1) in the brain, and it is ...
stems from damage to the
mammillary body The mammillary bodies are a pair of small round bodies, located on the undersurface of the brain that, as part of the diencephalon, form part of the limbic system. They are located at the ends of the anterior arches of the fornix. They consist o ...
, the
mammillothalamic fasciculus The mammillothalamic tract (mammillothalamic fasciculus, thalamomammillary fasciculus, bundle of Vicq d’Azyr) arises from cells in both the medial and lateral nuclei of the mammillary body and by fibers that are directly continued from the forn ...
or the thalamus.
Fatal familial insomnia Fatal insomnia is an extremely rare genetic (and even more rarely, sporadic) disorder that results in trouble sleeping as its hallmark symptom. The problems with sleeping typically start out gradually and worsen over time. Eventually, the patien ...
is a hereditary
prion Prions are misfolded proteins that have the ability to transmit their misfolded shape onto normal variants of the same protein. They characterize several fatal and transmissible neurodegenerative diseases in humans and many other animals. It ...
disease in which degeneration of the thalamus occurs, causing the patient to gradually lose their ability to sleep and progressing to a state of total
insomnia Insomnia, also known as sleeplessness, is a sleep disorder in which people have trouble sleeping. They may have difficulty falling asleep, or staying asleep as long as desired. Insomnia is typically followed by daytime sleepiness, low energy, ...
, which invariably leads to death. In contrast, damage to the thalamus can result in coma.


Additional images

File:Slide2GRE.JPG, Human brain dissection, showing the thalamus. File:Thalamus_-_DK_ATLAS.png , Human thalamus along with other subcortical structures, in glass brain. File:Thalamus_lateralgroup.jpg , Lateral group of the thalamic nuclei. File:Thalamus_medialgroup.jpg , Medial group of the thalamic nuclei.


See also

* 5-HT7 receptor *
Krista and Tatiana Hogan Krista and Tatiana Hogan (born October 25, 2006) are Canadians who are conjoined craniopagus twins. They are joined at the head and share a brain. They were born in Vancouver, British Columbia, and are the only unseparated conjoined twins of tha ...
- conjoined twins with joined thalami * List of regions in the human brain * Nonmotor region of the ventral nuclear group of the thalamus * Nucleus ventralis posterior lateralis pars oralis (VPLo), a region of the thalamus *
Primate basal ganglia system The basal ganglia form a major brain system in all species of vertebrates, but in primates (including humans) there are special features that justify a separate consideration. As in other vertebrates, the primate basal ganglia can be divided into ...
* Thalamic stimulator *
Thalamotomy Thalamotomy ( el, θάλαμος, thalamus, lit =chamber; el, τομή , tomē, lit=cut, slice) is a surgical procedure in which an opening is made into the thalamus to improve the overall brain function in patients. First introduced in the 1950 ...


References


External links

* {{Authority control Motor system Sensory systems