Anatomy & Organs

Subthalamus – Structure, Function & Diseases

Subthalamus

Beneath the thalamus lies arguably the most important part of the motor system: the subthalamus . It is located in the midbrain and contains nerve cell nuclei that control certain muscle activities. It represents a pale core; its shape is reminiscent of a lens. That part is one of the regions of the human brain that has so far hardly been examined. For this reason, doctors repeatedly speak of an “uncertain zone”.

What is the subthalamus?

The subthalamus, as the name suggests, hides beneath the thalamus. Or rather, it is found under the thalamus in the embryo ; as human development progresses, the subthalamus is pushed aside by a thick cord filled with a white substance.

The subthalamus thus ends up in the cerebrum and is found next to the putamen . His position is the main reason why he drives numerous anatomists to despair. The subthalamus is composed of the globus pallidus (“the pale nucleus”), the zona incerta (“the uncertain zone”), and the subthalamic nucleus. Even though the subthalamus was described as early as 1877, many medical professionals are still unsure of the role of the subthalamus.

Today there is therefore no precise information about its function; the descriptions and definitions are mostly pure speculation. The globus pallidus is pushed towards the putamen in the course of ontogenesis and, according to the experts, also plays an important role in motor processes.

Anatomy & Structure

Below the thalamus is the so-called zona incerta. The zona incerta represents a very small nucleus surrounded by a white matter above and below that physicians refer to as Forels H1 and H2 fields. The subthalamic nucleus connects to the transition area below and between the midbrain and diencephalon .

The nucleus, also known as Luys body, STN or Corpus subthalamicum Luysi, resembles a biconvex lens. Laterally, separated by the Capsula interna , lies the globus pallidus, which is reminiscent of a cone in shape. Its tip points down and towards the center. It forms the main nucleus of the subthalamus. Functionally, it belongs to the basal ganglia .

Function & Tasks

The subthalamus is part of the motor control system. It not only receives excitatory fiber access from the motor cortex, but also inhibitory impulses from the globus pallidus. The signals are sent to the inner segment and also to the substantia nigra. According to the physicians, the control loops are significantly more important here than individual structures. The basal ganlia influence the execution of movements. The main loop is responsible for motor skills .

This runs from the putamen via the globus pallidus to the thalamus. Because the thalamus is inhibited by the globus pallidus but itself inhibits the putamen, a double inhibition is subsequently created, allowing the thalamus to send its excitatory signals to the cortex. In the same process, the minor loops become the major loops. A major loop also includes the subthalamic nucleus. Thus, an inner pallidum segment is strengthened, resulting in an inner inhibition that acts on the thalamus. In this way, the secondary loop can prevent uncontrolled motor activity. However, it is also this secondary loop that – in the event of damage – can become a problem.

Auguste-Henri Forel, a brain researcher from Switzerland, described “the uncertain zone” almost 130 years ago. The zona incerta is mentioned in many textbooks, but only described very sparsely. In many cases, “the zone of uncertainty” is not even listed. One reason why numerous scientists are still unsure which functions actually emanate from the “uncertain zone”. However, there are guesses and speculations. In addition to influencing arousal, the zona incerta is thought to control the activities of the viscera and be responsible for maintaining movement.

Diseases

If the subthalamic nucleus is damaged, for example by an insult ( stroke ), the clinical picture of ballism develops. If the doctor diagnoses a one-sided disorder in the patient, he speaks of hemiballism. The affected person is no longer “master of his or her motor skills”. The arms or legs are unintentionally “thrown around”; a disorder that does not last long and predominantly affects only one side of the body.

This is the opposite side of the damaged hemisphere. However, the subthalamus also repeatedly influences the symptoms of Parkinson’s disease . The extent to which the subthalamus is responsible for this cannot be answered, however, and poses a mystery to many neuroscientists. However, it is known that a lack of dopamine in the subthalamus makes the symptoms worse. Compensating for the lack of dopamine improves resting tremor, which causes patients to tremble. Using a new method, however, it is possible that the brain stimulation can be influenced.

Sufferers receive electrodes that are inserted directly into the brain and continuously deliver electrical impulses, thus controlling the overactivity of the subthalamus. Other diseases that are related to the subthalamus are not yet known. Since so far only speculations can be made, the doctors are unsure whether the subthalamus could not also be responsible for other diseases that are associated with motor problems.

Lisa Newlon
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Hello! I am Lisa Newlon, and I am a medical writer and researcher with over 10 years of experience in the healthcare industry. I have a Master’s degree in Medicine, and my deep understanding of medical terminology, practices, and procedures has made me a trusted source of information in the medical world.