Striatum
Encyclopedia
The striatum, also known as the neostriatum or striate nucleus, is a subcortical (i.e., inside, rather than on the outside) part of the forebrain. It is the major input station of the basal ganglia system. The striatum, in turn, gets input from the cerebral cortex
. In primates (including humans), the striatum is divided by a white matter
tract called the internal capsule
into two sectors called the caudate nucleus
and putamen
. The term corpus striatum sometimes refers to the striatum combined with the globus pallidus
, a structure closely related to the putamen.
and Oskar
Vogt simplified the nomenclature by proposing the term striatum for all elements built with striatal elements (see primate basal ganglia system
): the caudate
, the putamen
, and the fundus striati, that ventral part linking the two preceding together ventrally to the inferior part of the internal capsule
.
The term neostriatum was forged by comparative anatomists comparing the subcortical structures between vertebrates, because it was thought to be a phylogenetically newer section of the corpus striatum. The term is still used by some sources, including Medical Subject Headings
.
s. It is composed of these neuronal cell types:
The striatum can also be differentiated based on immunochemical characteristics—particularly with regard to acetylcholinesterase
—into "compartments", consisting of 'striosomes' and 'matrisomes'.
forms a continuous and large mass, topographically separated by the internal capsule
into:
The dorsal striatum is a single entity closed and continuous. However, the observable anatomical subdivisions of the dorsal striatum (caudate nucleus and putamen) essentially induced by the internal capsule do not completely overlap with now accepted anatomo-functional subdivisions. The selective distribution of the axonal terminal arborisations of cortical sources differentiate the sensorimotor striatum, mainly putaminal but located in its dorsal part and in the lateroinferior part of the caudate. A great part of the remaining of the volume (essentially caudate) receiving from axonal endings from the frontal, parietal, temporal cortex forms the associative striatum. The separation between these two territories is rather clearcut and observable using calbindin
immunochemistry. A third entity, the most inferomedial, raises more problems as there is no general agreement about its border with the associative striatum.
Current evidence suggests that the dorsal striatum contributes directly to decision-making, especially to action selection and initiation, through the integration of sensorimotor, cognitive, and motivational/emotional information within specific corticostriatal circuits involving discrete regions of striatum. Studies in humans corroborate the research in animals suggesting that the dorsal striatum is an integral part of a circuit involved in decision-making. Accumulating evidence, primarily from neuroimaging but also neuropsychological investigations, has implicated the dorsal striatum in different aspects of motivational and learning processes that support goal-directed action. For instance, positron emission tomography (PET) studies report increases in dopamine release in the dorsal striatum (as measured by displacement of endogenous dopamine by radioligands) when participants are presented with potential rewards, such as the opportunity to gain money (Koepp et al., 1998; Zald et al., 2004) or even when presented with food stimuli while in a state of hunger (Volkow et al., 2002). Similarly, fMRI studies typically report increases in blood oxygenation level dependent (BOLD) responses in the dorsal striatum during anticipation of either primary (O'Doherty et al., 2002) or secondary (Knutson et al., 2001) rewards, much like the ventral striatum.
is strongly associated with emotional and motivational aspects of behavior.
The ventral striatum is clearly delineated by tracing the subicular (subiculum
) territory. This corresponds to the olfactory tubercle
and the nucleus accumbens
, which is not a nucleus
, but is a striatal part made up of striatal elements. The ventral striatum is generally associated with limbic structures, such as the amygdala, hippocampus, midline thalamus, and certain regions of the prefrontal cortex. In addition, the ventral striatum is strongly innervated by dopaminergic fibers from the ventral tegmental area (VTA), known as the mesolimbic dopamine system, and has the highest density of serotonergic inputs in the striatum.
In its present connotation, the term “ventral striatum” was introduced in 1975 by Heimer and Wilson to differentiate it from the dorsal, sensorimotor-related part of the striatum (i.e., the caudate-putamen complex). This inclusion of ventrally located striatal tissue in a “unified” striatum, along with the recognition of connectionally associated pallidal elements in the substantia innominata
and deep layers of the olfactory tubercle
(i.e., the ventral pallidum), has had great impact on the functional-anatomical concept of the basal ganglia
. Whereas traditionally, the basal ganglia were thought to be primarily involved in sensory-motor functions, it has now become accepted that the basal ganglia, as a result of their involvement in a set of parallel, functionally segregated basal ganglia-thalamocortical circuits, which primarily entertain the premotor and prefrontal cortical cortices, are also involved in cognitive and “limbic” functions.
Thus, in line with the characteristics of its inputs, the ventral striatum is functionally strongly associated with emotional and motivational aspects of behavior. Moreover, structural and functional disturbances of ventral striatal areas have been shown to be correlated with various forms of psychopathology, such as schizophrenia
, addictive behavior, and obsessive-compulsive disorder
.
Another well known afferent is the nigrostriatal connection arising from the neurons of the substantia nigra
pars compacta. While cortical axons synapse mainly on spine heads of spiny neurons, nigral axons synapse mainly on spine shafts.
In primates, the thalamostriatal afferent essentially comes from the center median-parafascicular complex of the thalamus
(see primate basal ganglia system
). This afferent is glutamatergic. The participation of truly intralaminar neurons is much more limited.
The striatum also receives afferents from other elements of the basal ganglia such as the subthalamic nucleus
(glutamatergic) or the external globus pallidus
(GABA
ergic).
of the substantia nigra
(SNc) and the pars reticulata
of substantia nigra (SNr). The neurons of this projection are inhibited by GABAergic synapses from the dorsal striatum. Among these targets, the GPe does not send axons outside the system. Others send axons to the superior colliculus
. Two others comprise the output to the thalamus, forming two separate channels: one through the internal segment of the globus pallidus to the ventral oralis nuclei of the thalamus and from there to the cortical supplementary motor area
(SMA) and another through the substantia nigra to the ventral anterior nuclei of the thalamus and from there to the frontal cortex and the occulomotor cortex.
The striatum is best known for its role in the planning and modulation of movement pathways but is also involved in a variety of other cognitive processes involving executive function.
In humans the striatum is activated by stimuli associated with reward, but also by aversive, novel, unexpected or intense stimuli, and cues associated with such events. Recent fMRI evidence suggests that the common property linking these stimuli, to which the striatum is reacting, is saliency
under the conditions of presentation. A number of other brain areas and circuits are also related to reward such as frontal areas. Research at the Wellcome Trust Centre for Neuroimaging
at UCL (University College London
) shows it to be associated with novelty-related decision making behaviors.
For sources regarding saliency of the reward pathway (thought to be related to dopamine) one can look to the work of Dr. John D. Salamone (early to late 1990s) and Wolfram Schultz. The ventral tegmental dopaminergic neurons that innervate portions of the striatum have long been accepted to be the site of rewarding feeling. Intracranial stimulation studies from the 1960s show implants in this brain area will elicit bar pressing from rats for many hours at a time.
However the collective works of researchers in the 1990s show that blocking dopamine receptors does not remove rewarding sensations, rather it affects how much the animal is willing to work, triggering more motivation to seek eventual reward rather than immediate reward.
results in loss of dopaminergic innervation to the striatum (and other basal ganglia) and a cascade of subsequent consequences. Atrophy
of the striatum is also involved in Huntington's disease
, choreas, choreoathetosis
, and dyskinesias. It is also thought that addiction
involves plasticity at striatal synapses.
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...
. In primates (including humans), the striatum is divided by a white matter
White matter
White matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
tract called the internal capsule
Internal capsule
The internal capsule is an area of white matter in the brain that separates the caudate nucleus and the thalamus from the lenticular nucleus. The internal capsule contains both ascending and descending axons....
into two sectors called the caudate nucleus
Caudate nucleus
The caudate nucleus is a nucleus located within the basal ganglia of the brains of many animal species. The caudate nucleus is an important part of the brain's learning and memory system.-Anatomy:...
and putamen
Putamen
The putamen is a round structure located at the base of the forebrain . The putamen and caudate nucleus together form the dorsal striatum. It is also one of the structures that comprises the basal ganglia. Through various pathways, the putamen is connected to the substantia nigra and globus pallidus...
. The term corpus striatum sometimes refers to the striatum combined with the globus pallidus
Globus pallidus
The globus pallidus also known as paleostriatum, is a sub-cortical structure of the brain. Topographically, it is part of the telencephalon, but retains close functional ties with the subthalamus - both of which are part of the extrapyramidal motor system...
, a structure closely related to the putamen.
History
In the seventeenth and eighteenth centuries, the term "corpus striatum" was used to designate many distinct, deep, infracortical elements of the hemisphere. In 1941, CécileCécile Vogt-Mugnier
Cecile Vogt-Mugnier was a French neurologist from Haute-Savoie.-Family:She obtained her medical doctorate in Paris and was the student of Pierre Marie. There she met her future husband, Oskar Vogt, when he came to Paris to work with Joseph Jules Déjérine...
and Oskar
Oskar Vogt
Oskar Vogt was a German physician and neurologist. He was born in Husum - Schleswig-Holstein...
Vogt simplified the nomenclature by proposing the term striatum for all elements built with striatal elements (see primate basal ganglia system
Primate basal ganglia system
The basal ganglia form a major brain system in all species of vertebrates, but the basal ganglia of primates have special features that justify a separate consideration. As in other vertebrates, the primate basal ganglia can be divided into striatal, pallidal, nigral, and subthalamic components...
): the caudate
Caudate nucleus
The caudate nucleus is a nucleus located within the basal ganglia of the brains of many animal species. The caudate nucleus is an important part of the brain's learning and memory system.-Anatomy:...
, the putamen
Putamen
The putamen is a round structure located at the base of the forebrain . The putamen and caudate nucleus together form the dorsal striatum. It is also one of the structures that comprises the basal ganglia. Through various pathways, the putamen is connected to the substantia nigra and globus pallidus...
, and the fundus striati, that ventral part linking the two preceding together ventrally to the inferior part of the internal capsule
Internal capsule
The internal capsule is an area of white matter in the brain that separates the caudate nucleus and the thalamus from the lenticular nucleus. The internal capsule contains both ascending and descending axons....
.
The term neostriatum was forged by comparative anatomists comparing the subcortical structures between vertebrates, because it was thought to be a phylogenetically newer section of the corpus striatum. The term is still used by some sources, including Medical Subject Headings
Medical Subject Headings
Medical Subject Headings is a comprehensive controlled vocabulary for the purpose of indexing journal articles and books in the life sciences; it can also serve as a thesaurus that facilitates searching...
.
Cell types
The striatum is heterogeneous in terms of neuronNeuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s. It is composed of these neuronal cell types:
- Medium spiny neurons so called due to the presence of spines on the dendrites, and making up 96% of the striatum.
- Deiters' neuronsOtto Friedrich Karl DeitersOtto Friedrich Karl Deiters was a German neuroanatomist. He was born in Bonn, studied at the University of Bonn, and spent most of his professional career in Bonn...
(2%) with large, minimally branched arborizations looking like pallidonigral neurons. - CholinergicAcetylcholineThe chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...
interneurons (1%). In primates, they are the tonically active neurons, and morphologically entirely different from those observed in rodents. These briefly stop firing in response to behaviorally-salient and rewardReward systemIn neuroscience, the reward system is a collection of brain structures which attempts to regulate and control behavior by inducing pleasurable effects...
-related events. - GABAergic parvalbuminParvalbuminParvalbumin is a calcium-binding albumin protein with low molecular weight .It has three EF hand motifs and is structurally related to calmodulin and troponin C...
expressing interneurons, which are fast-spiking, and express dopamine receptorDopamine receptorDopamine receptors are a class of metabotropic G protein-coupled receptors that are prominent in the vertebrate central nervous system . The neurotransmitter dopamine is the primary endogenous ligand for dopamine receptors....
s. - GABAergic calretininCalretininCalretinin also known as 29 kDa calbindin is a vitamin D-dependent calcium-binding protein involved in calcium signaling. In humans, the calretinin protein is encoded by the CALB2 gene.- Function :...
expressing interneurons. - GABAergic somatostatinSomatostatinSomatostatin is a peptide hormone that regulates the endocrine system and affects neurotransmission and cell proliferation via interaction with G-protein-coupled somatostatin receptors and inhibition of the release of numerous secondary hormones.Somatostatin...
expressing interneurons, which are low-threshold-spiking and express dopamine receptors.
Anatomical subdivisions
The striatum is spatially organized according to several criteria. It is important to note that the distinction between a dorsal and ventral striatum on the basis of specific cortical, thalamic, and dopaminergic inputs does not provide sharply defined borders between these striatal areas. To date, few structural or functional markers uniquely characteristic for either of the two regions have been identified. In the literature, dorsal and ventral striatum have been virtually equalized with the distinction between the caudate-putamen complex (dorsal) and the nucleus accumbens (ventral), respectively. However, the ventral striatum as defined on the basis of the aforementioned limbic inputs, as well as based on cyto- and chemoarchitectonic characteristics, occupies a more extensive striatal area than the nucleus accumbens alone and extends more dorsally and caudally into the ventral parts of the caudate nucleus and putamen.The striatum can also be differentiated based on immunochemical characteristics—particularly with regard to acetylcholinesterase
Acetylcholinesterase
"Acetylcholinesterase, also known as AChE or acetylcholine acetylhydrolase, is an enzyme that degrades the neurotransmitter acetylcholine, producing choline and an acetate group. It is mainly found at neuromuscular junctions and cholinergic nervous system, where its activity serves to terminate...
—into "compartments", consisting of 'striosomes' and 'matrisomes'.
Dorsal striatum
The dorsal striatumDorsal striatum
The dorsal striatum, corpus striatum or striated body is a compound structure consisting of the caudate nucleus, and the lentiform nucleus...
forms a continuous and large mass, topographically separated by the internal capsule
Internal capsule
The internal capsule is an area of white matter in the brain that separates the caudate nucleus and the thalamus from the lenticular nucleus. The internal capsule contains both ascending and descending axons....
into:
- The caudateCaudate nucleusThe caudate nucleus is a nucleus located within the basal ganglia of the brains of many animal species. The caudate nucleus is an important part of the brain's learning and memory system.-Anatomy:...
(medially) - The putamenPutamenThe putamen is a round structure located at the base of the forebrain . The putamen and caudate nucleus together form the dorsal striatum. It is also one of the structures that comprises the basal ganglia. Through various pathways, the putamen is connected to the substantia nigra and globus pallidus...
(laterally) - The fundus (ventrally), linking the caudate nucleus and the putamen.
The dorsal striatum is a single entity closed and continuous. However, the observable anatomical subdivisions of the dorsal striatum (caudate nucleus and putamen) essentially induced by the internal capsule do not completely overlap with now accepted anatomo-functional subdivisions. The selective distribution of the axonal terminal arborisations of cortical sources differentiate the sensorimotor striatum, mainly putaminal but located in its dorsal part and in the lateroinferior part of the caudate. A great part of the remaining of the volume (essentially caudate) receiving from axonal endings from the frontal, parietal, temporal cortex forms the associative striatum. The separation between these two territories is rather clearcut and observable using calbindin
Calbindin
Calbindin refers to several calcium-binding proteins. They were originally described as vitamin D-dependent calcium-binding proteins in the intestine and kidney in the chick and mammals...
immunochemistry. A third entity, the most inferomedial, raises more problems as there is no general agreement about its border with the associative striatum.
Current evidence suggests that the dorsal striatum contributes directly to decision-making, especially to action selection and initiation, through the integration of sensorimotor, cognitive, and motivational/emotional information within specific corticostriatal circuits involving discrete regions of striatum. Studies in humans corroborate the research in animals suggesting that the dorsal striatum is an integral part of a circuit involved in decision-making. Accumulating evidence, primarily from neuroimaging but also neuropsychological investigations, has implicated the dorsal striatum in different aspects of motivational and learning processes that support goal-directed action. For instance, positron emission tomography (PET) studies report increases in dopamine release in the dorsal striatum (as measured by displacement of endogenous dopamine by radioligands) when participants are presented with potential rewards, such as the opportunity to gain money (Koepp et al., 1998; Zald et al., 2004) or even when presented with food stimuli while in a state of hunger (Volkow et al., 2002). Similarly, fMRI studies typically report increases in blood oxygenation level dependent (BOLD) responses in the dorsal striatum during anticipation of either primary (O'Doherty et al., 2002) or secondary (Knutson et al., 2001) rewards, much like the ventral striatum.
Ventral striatum
The ventral striatumVentral striatum
The ventral striatum is generally considered that part of the striatum that is connectionally associated with limbic structures, such as the amygdala, hippocampus, midline thalamus, and certain regions of the prefrontal cortex...
is strongly associated with emotional and motivational aspects of behavior.
- The nucleus accumbensNucleus accumbensThe nucleus accumbens , also known as the accumbens nucleus or as the nucleus accumbens septi , is a collection of neurons and forms the main part of the ventral striatum...
- The olfactory tubercleOlfactory tubercleThe olfactory tubercle is a structure involved in Olfaction.It is present in humans, but much smaller than it is in some other animals.It is a frequent subject of research.-External links:...
The ventral striatum is clearly delineated by tracing the subicular (subiculum
Subiculum
The subiculum is the most inferior component of the hippocampal formation. It lies between the entorhinal cortex and the CA1 subfield of the hippocampus proper.-Paths:...
) territory. This corresponds to the olfactory tubercle
Olfactory tubercle
The olfactory tubercle is a structure involved in Olfaction.It is present in humans, but much smaller than it is in some other animals.It is a frequent subject of research.-External links:...
and the nucleus accumbens
Nucleus accumbens
The nucleus accumbens , also known as the accumbens nucleus or as the nucleus accumbens septi , is a collection of neurons and forms the main part of the ventral striatum...
, which is not a nucleus
Nucleus (neuroanatomy)
In neuroanatomy, a nucleus is a brain structure consisting of a relatively compact cluster of neurons. It is one of the two most common forms of nerve cell organization, the other being layered structures such as the cerebral cortex or cerebellar cortex. In anatomical sections, a nucleus shows up...
, but is a striatal part made up of striatal elements. The ventral striatum is generally associated with limbic structures, such as the amygdala, hippocampus, midline thalamus, and certain regions of the prefrontal cortex. In addition, the ventral striatum is strongly innervated by dopaminergic fibers from the ventral tegmental area (VTA), known as the mesolimbic dopamine system, and has the highest density of serotonergic inputs in the striatum.
In its present connotation, the term “ventral striatum” was introduced in 1975 by Heimer and Wilson to differentiate it from the dorsal, sensorimotor-related part of the striatum (i.e., the caudate-putamen complex). This inclusion of ventrally located striatal tissue in a “unified” striatum, along with the recognition of connectionally associated pallidal elements in the substantia innominata
Substantia innominata
The substantia innominata of Meynert is a stratum in the human brain consisting partly of gray and partly of white substance, which lies below the anterior part of the thalamus and lentiform nucleus...
and deep layers of the olfactory tubercle
Olfactory tubercle
The olfactory tubercle is a structure involved in Olfaction.It is present in humans, but much smaller than it is in some other animals.It is a frequent subject of research.-External links:...
(i.e., the ventral pallidum), has had great impact on the functional-anatomical concept of the basal ganglia
Basal ganglia
The basal ganglia are a group of nuclei of varied origin in the brains of vertebrates that act as a cohesive functional unit. They are situated at the base of the forebrain and are strongly connected with the cerebral cortex, thalamus and other brain areas...
. Whereas traditionally, the basal ganglia were thought to be primarily involved in sensory-motor functions, it has now become accepted that the basal ganglia, as a result of their involvement in a set of parallel, functionally segregated basal ganglia-thalamocortical circuits, which primarily entertain the premotor and prefrontal cortical cortices, are also involved in cognitive and “limbic” functions.
Thus, in line with the characteristics of its inputs, the ventral striatum is functionally strongly associated with emotional and motivational aspects of behavior. Moreover, structural and functional disturbances of ventral striatal areas have been shown to be correlated with various forms of psychopathology, such as schizophrenia
Schizophrenia
Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
, addictive behavior, and obsessive-compulsive disorder
Obsessive-compulsive disorder
Obsessive–compulsive disorder is an anxiety disorder characterized by intrusive thoughts that produce uneasiness, apprehension, fear, or worry, by repetitive behaviors aimed at reducing the associated anxiety, or by a combination of such obsessions and compulsions...
.
Inputs (afferent connections)
The most important afferent in terms of quantity of axons is the corticostriatal connection. Many parts of the neocortex innervate the dorsal striatum. The cortical pyramidal neurons projecting to the striatum are located in layers II-VI, but the most dense projections come from layer V. They end mainly on the spines of the spiny neurons. They are glutamatergic, exciting striatal neurons.Another well known afferent is the nigrostriatal connection arising from the neurons of the substantia nigra
Substantia nigra
The substantia nigra is a brain structure located in the mesencephalon that plays an important role in reward, addiction, and movement. Substantia nigra is Latin for "black substance", as parts of the substantia nigra appear darker than neighboring areas due to high levels of melanin in...
pars compacta. While cortical axons synapse mainly on spine heads of spiny neurons, nigral axons synapse mainly on spine shafts.
In primates, the thalamostriatal afferent essentially comes from the center median-parafascicular complex of the thalamus
Thalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
(see primate basal ganglia system
Primate basal ganglia system
The basal ganglia form a major brain system in all species of vertebrates, but the basal ganglia of primates have special features that justify a separate consideration. As in other vertebrates, the primate basal ganglia can be divided into striatal, pallidal, nigral, and subthalamic components...
). This afferent is glutamatergic. The participation of truly intralaminar neurons is much more limited.
The striatum also receives afferents from other elements of the basal ganglia such as the subthalamic nucleus
Subthalamic nucleus
The subthalamic nucleus is a small lens-shaped nucleus in the brain where it is, from a functional point of view, part of the basal ganglia system. Anatomically, it is the major part of subthalamus. As suggested by its name, the subthalamic nucleus is located ventral to the thalamus. It is also...
(glutamatergic) or the external globus pallidus
Globus pallidus
The globus pallidus also known as paleostriatum, is a sub-cortical structure of the brain. Topographically, it is part of the telencephalon, but retains close functional ties with the subthalamus - both of which are part of the extrapyramidal motor system...
(GABA
Gabâ
Gabâ or gabaa, for the people in many parts of the Philippines), is the concept of a non-human and non-divine, imminent retribution. A sort of negative karma, it is generally seen as an evil effect on a person because of their wrongdoings or transgressions...
ergic).
Targets (efferent connections)
The basal ganglia core is made up of the striatum along with the regions to which it projects directly, via the striato-pallidonigral bundle. The striato-pallidonigral bundle is a very dense bundle of sparsely myelinated axons, giving a whitish appearance. This projection comprises successively the external globus pallidus (GPe), the internal globus pallidus (GPi), the pars compactaPars compacta
-Anatomy:In humans, the nerve cell bodies of the pars compacta are coloured black by the pigment neuromelanin. The degree of pigmentation increases with age. This pigmentation is visible as a distinctive black stripe in brain sections and is the origin of the name given to this area. The neurons...
of the substantia nigra
Substantia nigra
The substantia nigra is a brain structure located in the mesencephalon that plays an important role in reward, addiction, and movement. Substantia nigra is Latin for "black substance", as parts of the substantia nigra appear darker than neighboring areas due to high levels of melanin in...
(SNc) and the pars reticulata
Pars reticulata
-Anatomy:Neurons in the pars reticulata are much less densely packed than those in the pars compacta . They are smaller and thinner than the dopaminergic neurons and conversely identical and morphologically similar to the pallidal neurons...
of substantia nigra (SNr). The neurons of this projection are inhibited by GABAergic synapses from the dorsal striatum. Among these targets, the GPe does not send axons outside the system. Others send axons to the superior colliculus
Superior colliculus
The optic tectum or simply tectum is a paired structure that forms a major component of the vertebrate midbrain. In mammals this structure is more commonly called the superior colliculus , but, even in mammals, the adjective tectal is commonly used. The tectum is a layered structure, with a...
. Two others comprise the output to the thalamus, forming two separate channels: one through the internal segment of the globus pallidus to the ventral oralis nuclei of the thalamus and from there to the cortical supplementary motor area
Supplementary motor area
The supplementary motor area is a part of the sensorimotor cerebral cortex . It was included, on purely cytoarchitectonic arguments, in area 6 of Brodmann and the Vogts...
(SMA) and another through the substantia nigra to the ventral anterior nuclei of the thalamus and from there to the frontal cortex and the occulomotor cortex.
Function
Metabotropic dopamine receptors are present both on spiny neurons and on cortical axon terminals. Second messenger cascades triggered by activation of these dopamine receptors can modulate pre- and postsynaptic function, both in the short term and in the long term.The striatum is best known for its role in the planning and modulation of movement pathways but is also involved in a variety of other cognitive processes involving executive function.
In humans the striatum is activated by stimuli associated with reward, but also by aversive, novel, unexpected or intense stimuli, and cues associated with such events. Recent fMRI evidence suggests that the common property linking these stimuli, to which the striatum is reacting, is saliency
Salience (neuroscience)
The salience of an item – be it an object, a person, a pixel, etc – is the state or quality by which it stands out relative to its neighbours...
under the conditions of presentation. A number of other brain areas and circuits are also related to reward such as frontal areas. Research at the Wellcome Trust Centre for Neuroimaging
Wellcome Trust Centre for Neuroimaging
The Wellcome Trust Centre for Neuroimaging at University College London is an interdisciplinary centre for neuroimaging research based in London, United Kingdom.Principal investigators working at the Centre include Professors Ray Dolan, Jon Driver, Richard Frackowiak,...
at UCL (University College London
University College London
University College London is a public research university located in London, United Kingdom and the oldest and largest constituent college of the federal University of London...
) shows it to be associated with novelty-related decision making behaviors.
For sources regarding saliency of the reward pathway (thought to be related to dopamine) one can look to the work of Dr. John D. Salamone (early to late 1990s) and Wolfram Schultz. The ventral tegmental dopaminergic neurons that innervate portions of the striatum have long been accepted to be the site of rewarding feeling. Intracranial stimulation studies from the 1960s show implants in this brain area will elicit bar pressing from rats for many hours at a time.
However the collective works of researchers in the 1990s show that blocking dopamine receptors does not remove rewarding sensations, rather it affects how much the animal is willing to work, triggering more motivation to seek eventual reward rather than immediate reward.
Pathology
Parkinson's diseaseParkinson's disease
Parkinson's disease is a degenerative disorder of the central nervous system...
results in loss of dopaminergic innervation to the striatum (and other basal ganglia) and a cascade of subsequent consequences. Atrophy
Atrophy
Atrophy is the partial or complete wasting away of a part of the body. Causes of atrophy include mutations , poor nourishment, poor circulation, loss of hormonal support, loss of nerve supply to the target organ, disuse or lack of exercise or disease intrinsic to the tissue itself...
of the striatum is also involved in Huntington's disease
Huntington's disease
Huntington's disease, chorea, or disorder , is a neurodegenerative genetic disorder that affects muscle coordination and leads to cognitive decline and dementia. It typically becomes noticeable in middle age. HD is the most common genetic cause of abnormal involuntary writhing movements called chorea...
, choreas, choreoathetosis
Choreoathetosis
Choreoathetosis is the occurrence of involuntary movements in a combination of chorea and athetosis ....
, and dyskinesias. It is also thought that addiction
Substance use disorder
Substance use disorders include substance abuse and substance dependence. In DSM-IV, the conditions are formally diagnosed as one or the other, but it has been proposed that DSM-5 combine the two into a single condition called "Substance-use disorder"....
involves plasticity at striatal synapses.