Subthalamic nucleus

At the Subthalamic nucleus it is a nucleus (lat. nucleus) that lies under (lat. sub) the thalamus, the largest part of the diencephalon. In the professional world today the abbreviation is mostly used STN used. His earlier nickname, Luysi body, however, goes back to its discoverer.

What is the subthalamic nucleus?

The subthalamic nucleus is part of the subthalamus alongside the globus pallidus and the zona incerta. This area belonging to the brain stem lies in the interbrain (medical diencephalon) in the transition to the midbrain.

Due to its comparable functionality, however, it is assigned to the basal ganglia, which are usually located under the cerebral cortex. They are diencephalic or endbrain nuclei that, like the subthalamic nucleus, play an important role in motor processes in the body. There is a very close connection between the globus pallidus, a pale nucleus also called the pallidum, and the subthalamic nucleus.

Both are mutually interconnected and form a kind of oscillating circuit. They receive and send each other signals on the basis of which certain movements of the human body are then inhibited or allowed. This has an effect on the four limbs, in particular the sections near the torso or those towards the middle of the body.

Anatomy & structure

The double subthalamic nucleus itself is reminiscent of a biconvex lens with its exterior and is present in the left and right hemispheres of the brain. However, it is only located directly under the thalamus during the embryonic phase. Then the entire area of ​​the subthalamus is pushed towards the cerebrum by the neighboring internal capsule, a collection of white brain matter including nerve fibers, in the course of development.

The subthalamus is located in the anterior region of the diencephalon and is also regarded as part of the extra pyramidal motor system, EPMS for short. These are motor pathways that pull into the spinal cord and activate the muscles of the trunk and limbs there. The brain region around the subthalamus is one of the least explored areas of the entire brain. However, while specific information is now available about the subthalamic nucleus and the globus pallidus, little is known about the zona incerta.

Function & tasks

The main function of the subthalamic nucleus is to have an inhibiting effect on certain movements of the human body. This effect ensures the possibility of using all limbs arbitrarily and above all in a targeted manner. Without the movement-inhibiting effect of the subthalamic nucleus, movements would only be possible in an uncontrolled manner and an independent or everyday life would be almost impossible.

The process is controlled by a complex interconnection of the basal ganglia responsible for motor function and other areas of the brain stem. This interconnection can be compared with interlocking gears that form a main loop with several secondary loops. The process is driven by counteracting signals. These have either an inhibiting or exciting effect and use glutamate as a neurotransmitter.

The signals reaching the subthalamic nucleus originate mainly from fiber accesses in the cerebral cortex and the adjacent globus pallidus. However, while stimulating impulses arrive from the cerebral cortex, the globus pallidus sends inhibitory impulses. The nucleus subthalamicus reacts to the latter by sending back stimulating signals and, through the existing interaction, ensures that the globus pallidus then sends inhibitory impulses to the thalamus again. The subthalamic nucleus indirectly counteracts unregulated movements and controls the human gross motor skills.

The movement-inhibiting functionality of the subthalamic nucleus is now also part of Parkinson's research. Although the exact relationships have not yet been conclusively determined, it has been proven that the characteristic tremor, the so-called resting tremor, of Parkinson's patients can be noticeably reduced by an external influence on the subthalamic nucleus. For this purpose, microelectrodes are implanted that calm the overactive subthalamic nucleus in those affected and consequently also reduce tremors.

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Diseases

The only known disease of the subthalamic nucleus, which also occurs extremely rarely, is ballism. This manifests itself with uncontrolled and extraordinarily violent movements of the arms and legs, in rare cases also of the pelvis and shoulder girdle.

There is no control over the affected limbs and even injuries to yourself cannot be ruled out. However, the symptoms do not show up during sleep.

The ballism usually only extends to one side of the body, so that hemiballism is also often referred to. In this case, the half of the patient's body is affected, which is on the opposite side of the subthalamic nucleus, which is responsible for the disease. Ballism is caused by a disruption or injury to the core. This can be caused, for example, by a brain tumor including metastases, a cerebral infarction or a stroke. Also possible are encephalitis, neurosyphilis and injuries sustained by the patient during a previous neurosurgical procedure.

Ballism can be reliably diagnosed using CT or MRI. This is usually followed by treatment with an anti-epileptic or a neuroleptic. If this therapy is unsuccessful, various surgical interventions are still possible. The chances of recovery depend heavily on the cause and can hardly be estimated due to the small number of cases so far. They range from a spontaneous weakening of symptoms to paralysis of certain muscle groups.