The striatum, or corpus striatum, is a nucleus in the subcortical basal ganglia of the forebrain. The striatum is a critical component of the motor and reward systems; receives glutamatergic and dopaminergic inputs from different sources; and serves as the primary input to the rest of the basal ganglia.
The basal ganglia are a group of subcortical nuclei, of varied origin, in the brains of vertebrates, including humans, which are situated at the base of the forebrain and top of the midbrain. There are some differences in the basal ganglia of primates. Basal ganglia are strongly interconnected with the cerebral cortex, thalamus, and brainstem, as well as several other brain areas. The basal ganglia are associated with a variety of functions, including control of voluntary motor movements, procedural learning, habit learning, eye movements, cognition, and emotion.
The globus pallidus 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 rodents as the entopeduncular nucleus. It is part of the telencephalon, but retains close functional ties with the subthalamus in the diencephalon – both of which are part of the extrapyramidal motor system. The globus pallidus is a major component of the basal ganglia, with principal inputs from the striatum, and principal direct outputs to the thalamus and the substantia nigra. The latter is made up of similar neuronal elements, has similar afferents from the striatum, similar projections to the thalamus, and has a similar synaptology. Neither receives direct cortical afferents, and both receive substantial additional inputs from the intralaminar thalamus.
The internal capsule is a white matter structure situated in the inferomedial part of each cerebral hemisphere of the brain. It carries information past the basal ganglia, separating the caudate nucleus and the thalamus from the putamen and the globus pallidus. The internal capsule contains both ascending and descending axons, going to and coming from the cerebral cortex. It also separates the caudate nucleus and the putamen in the dorsal striatum, a brain region involved in motor and reward pathways.
In the anatomy of the brain, the centromedian nucleus, also known as the centrum medianum, is a part of the intralaminar nucleus (ILN) of the thalamus. There are two centromedian nuclei arranged bilaterally.
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 dorsal thalamic structure. It is separated from the thalamus by the external medullary lamina. Reticular cells are GABAergic, and have discoid dendritic arbors in the plane of the nucleus.
The lentiform nucleus, or lenticular nucleus, comprises the putamen and the globus pallidus within the basal ganglia. With the caudate nucleus, it forms the striatum. It is a large, lens-shaped mass of gray matter just lateral to the internal capsule.
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.
The substantia innominata also innominate substance, or substantia innominata of Meynert is a series of layers in the human brain consisting partly of gray and partly of white matter, which lies below the anterior part of the thalamus and lentiform nucleus. It is included as part of the anterior perforated substance. It is part of the basal forebrain structures and includes the nucleus basalis. A portion of the substantia innominata, below the globus pallidus is considered as part of the extended amygdala.
The basal ganglia form a major brain system in all species of vertebrates, but in primates there are 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. In primates, however, there are two pallidal subdivisions called the external globus pallidus (GPe) and internal globus pallidus (GPi). Also in primates, the dorsal striatum is divided by a large tract called the internal capsule into two masses named the caudate nucleus and the putamen—in most other species no such division exists, and only the striatum as a whole is recognized. Beyond this, there is a complex circuitry of connections between the striatum and cortex that is specific to primates. This complexity reflects the difference in functioning of different cortical areas in the primate brain.
The mammillothalamic tract arises from cells in both the medial and lateral nuclei of the mammillary body and by fibers that are directly continued from the fornix.
The ventral anterior nucleus (VA) is a nucleus of the thalamus. It acts with the anterior part of the ventral lateral nucleus to modify signals from the basal ganglia.
The ventral lateral nucleus (VL) is a nucleus in the ventral nuclear group of the thalamus.
The thalamic fasciculus is a component of the subthalamus. It is synonymous with field H1 of Forel. Nerve fibres form a tract containing cerebellothalamic (crossed) and pallidothalamic (uncrossed) fibres, that is insinuated between the thalamus and the zona incerta.
The internal globus pallidus and the external globus pallidus (GPe) make up the globus pallidus. The GPi is one of the output nuclei of the basal ganglia. The GABAergic neurons send their axons to the ventral anterior nucleus (VA) and the ventral lateral nucleus (VL) in the dorsal thalamus, to the centromedian complex, and to the pedunculopontine complex.
The dentatothalamic tract is a tract which connects the dentate nucleus and the thalamus while sending collaterals to the red nucleus.
The subthalamic fasciculus is a tract which connects the subthalamic nucleus (STN) and the globus pallidus (GP).
The pallidothalamic tracts are a part of the basal ganglia. They provide connectivity between the internal globus pallidus (GPi) and the thalamus, primarily the ventral anterior nucleus and the ventral lateral nucleus.
The ventral pallidum (VP) is a structure within the basal ganglia of the brain. It is an output nucleus whose fibres project to thalamic nuclei, such as the ventral anterior nucleus, the ventral lateral nucleus, and the medial dorsal nucleus. The VP is a core component of the reward system which forms part of the limbic loop of the basal ganglia, a pathway involved in the regulation of motivational salience, behavior, and emotions. It is involved in addiction.
The fields of Forel are areas in a deep part of the brain known as the diencephalon. They are below the thalamus and consist of three defined, white matter areas of the subthalamus. These three regions are also named "H fields":
