SUBTHALAMUS: STRUCTURE, FUNCTIONS AND DISEASES - NEUROPSYCHOLOGY - 2025

The subthalamus is a region of the diencephalon that is associated with motor functions. As its name suggests, it is located below the thalamus; between the latter and the tegmentum of the midbrain. Despite its small size, this brain structure is enormously complex, containing different groups of nerve cells.

The subthalamus is shaped like a biconvex lens (like two convex surfaces, being thinner at the ends than in the center). Its most important and studied part is the subthalamic nucleus, which establishes connections with other brain regions. For example, it has fundamental connections with the striatum to regulate muscle activity.

Different somatic and sensory pathways cross the subthalamus. They mainly target the cerebellum, thalamus, and basal ganglia.

On the other hand, the subthalamus also includes many essential tracts that travel from the tegmentum to the thalamic nuclei. Some of them are the cranial ends of the medial, spinal and trigeminal lemnisci.

Location of the subthalamus

The subthalamus is located in a transitional area between the brainstem and the cerebral hemispheres.

If it is located in the ventral part of the thalamus, and is limited posteriorly by the midbrain. In the anterior area of ​​the subthalamus is the hypothalamus. It is located medial to the internal capsule. Towards its caudal part it is limited to the tegmentum of the midbrain, and includes the rostral prolongation of the substantia nigra and the red nucleus.

In the area ventrolateral to the subthalamus are the descending fibers of the internal capsule towards the cerebral peduncle.

During embryonic development, the subthalamus is an extension of the hypothalamus. They are only separated by a few fibers of white matter mainly from the inner capsule. Caudally, it is separated from the thalamus by the intrathalamic limiting zone (ZLI).

Parts (structure)

The subthalamus is a brain region made up of several nuclei of gray and white matter. Anatomically, it is considered a prolongation of the midbrain integrated into the interior of the diencephalon.

The subthalamus is mainly made up of two structures: the subthalamic nucleus and the uncertain zone. The subthalamic nucleus is ventral to the latter.

Subthalamic nucleus or nucleus of Luys

The subthalamic nucleus consists of an ovoid mass of gray matter that is located in the central part of the uncertain zone. It is separated from the latter by Forel's H2 field.

In its lateral part is the internal capsule, and caudally it is associated with the substantia nigra.

It is a grouping of gray matter made up of neurons of medium size and various shapes. This nucleus regulates motor activities through its interconnections with the basal ganglia. Your neurons secrete and receive glutamate, a substance that exerts excitatory effects. Thus, they activate neurons of the globus pallus and the substantia nigra.

Uncertain area

It is a thin sheet of gray matter, located parallel to the hypothalamic sulcus. It is separated from the latter by Forel's H1 and H fields. Dorsolateral to it is the reticular nucleus of the thalamus. At its medial end there is a group of neurons that constitute the nucleus of the tegmental field.

This region joins the diencephalon with the midbrain to coordinate vision with our movements, being involved in the extrapyramidal pathway. To do this, it receives information from the motor cortex.

Some authors consider it as a continuation of the reticular formation of the midbrain.

Between the neuronal groups of the subthalamus, the cranial ends of the red nuclei and the substantia nigra are observed (Snell, 2007).

Within the subthalamus there is also the subthalamic fasciculus, a structure composed of fibers that join the globe pallidus with the subthalamic nucleus.

On the other hand, Forel fields are also included, which are made up of three specific areas of white matter called "H fields". These are:

- The H1 field, an area of ​​white matter made up of the lenticular loop, the lenticular fascicle, and the cerebellum-thalamic tracts. They are projections that reach the thalamus from the basal ganglia and the cerebellum.

- The H2 field or lenticular fascicle, which carry projections of the globe pallidus to the thalamus and the subthalamic nucleus.

- The H or H3 field is a large area of ​​gray and white matter, a mixture of the pale-thalamic tracts of the lenticular fascicle and the lenticular loop.

Connections

The subthalamus establishes efferent connections (that is, sends information) with the striatum (caudate nucleus and putamen), the dorsal thalamus, the substantia nigra, and the red nucleus.

While receiving information or maintaining afferent connections with the substantia nigra and the striatum. Also, exchange information with the pale balloon.

Features

The subthalamus is known as the motor region of the diencephalon. This area has the nuclei of the extrapyramidal motor system, which is what directs involuntary motor functions such as reflexes, locomotion, postural control, etc. Therefore, functionally the subthalamus belongs to the extrapyramidal system.

On the other hand, it regulates the impulses of the optic nerves and vestibular nerves (those that are in charge of balance and orientation). It transmits these impulses to the pale globe.

Diseases

Lesions or degenerations of the subthalamus from certain diseases cause motor disorders. Specifically, a relationship has been found between damage to the subthalamic nucleus and the appearance of chorea. Chorea or dyskinesia is a neurological disorder characterized by involuntary movements of the limbs.

They are due to non-rhythmic, non-repetitive, irregular contractions that seem to travel from one muscle to the next. The movements resemble playing the piano or doing a dance.

Alterations of the subthalamic nucleus can be associated with two types of chorea:

- Huntington's chorea: also called Huntington's disease, it has a hereditary origin and is chronic. It is characterized by a progressive appearance of motor and cognitive alterations, in addition to psychiatric symptoms.

At first the motor restlessness or chorea is not observed, but little by little it becomes more noticeable. It is also accompanied by problems with motor control, coordination, articulation of language, and swallowing.

- Sydenham's chorea: or minor chorea, it is an infectious disease that produces uncontrollable and purposeless movements in the face, shoulders, arms, hands, legs and trunk. They are seen as spasms that disappear when the patient sleeps.

This disease arises from the attack of a bacterium called Streptococcus pyogenes on the central nervous system.

References

1. Hamani, C., Saint-Cyr, JA, Fraser, J., Kaplitt, M., & Lozano, AM (2004). The subthalamic nucleus in the context of movement disorders. Brain, 127 (1), 4-20.
2. Fields of Forel. (sf). Retrieved on April 26, 2017, from Wikipedia: en.wikipedia.org.
3. Issa, N. (sf). Hypothalamus, Subthalamus, and Epithalamus. Retrieved on April 26, 2017, from Doc Neuro: docneuro.com.
4. Snell, R. (2007). Clinical neuroanatomy, 6th edition. Buenos Aires: Panamerican Medical.
5. Subthalamus. (sf). Retrieved on April 26, 2017, from Be brain: bebrainid.wixsite.com.
6. Subthalamus. (sf). Retrieved on April 26, 2017, from Wikipedia: en.wikipedia.org.