The thalamus is a part of the diencephalon. It is composed of different nucleus areas.
What is the thalamus
The dorsal thalamus represents a component of the diencephalon. Other subregions include the hypothalamus including the pituitary gland, the subthalamus, and the epithalamus including the pineal gland. The thalamus exists once in each brain hemisphere. It has a bean-shaped structure and is composed of several nuclear areas. In these areas there is a strong connection to the cortex of the cerebrum. Apart from the olfactory pathway, all ascending pathways that are important for sensory-sensory information require circuitry in the thalamus. For this reason, this area of the brain also bears the name “gateway to consciousness.”
Anatomy and structure
Anatomically, the thalamus is found in the center of the diencephalon. There is an adjacency to the 3rd ventricle. Composed, the thalamus is made up of two halves. These reach the size of a pigeon egg. The area Adhaesio interthalamica mostly provides a connection between the left and the right thalamus. The thalamus consists of over one hundred nuclear areas, also known as nuclei. These areas are divided into two groups. These are the specific and the non-specific thalamic nuclei. In the case of the specific nuclei, there is a connection to the areas of the cerebral cortex that can be clearly delineated. After the nuclei receive sensory and sensitive impulses from the peripheral areas, they provide for their transmission to the cerebrum after switching. Among the most important specific nuclei are the nucleus ventralis posterior, which serves as a switching point of sensory signals for touch and depth sensitivity, and the nucleus ventralis anterolalis, which processes motor signals. Important for higher cognitive abilities is the medial thalamic nucleus, while the anterior thalamic nucleus plays a significant role in limbic system activities. Other specific nuclei include the corpus geniculatum mediale, which is an important circuit for the auditory pathway, the corpus geniculatum laterale, which performs the same function for the visual pathway, and the pulvinar. The latter is important for memory, perception and language. In the case of the nonspecific nuclei, there is only a weak connection or even no connection at all with the cerebral cortex. Information is fed to them from the formatio reticularis, basal ganglia, and cerebellum (cerebellum). There is also a connection to the specific thalamic nuclei. The nonspecific nuclei include the nuclei mediani and the nuclei interlaminares. While the nuclei mediani have a close connection with the limbic and olfactory systems, the nuclei interlaminares are important for controlling the human state of consciousness. The nonspecific nuclei have the ability to take over different areas when activated. Certain connections are important for attention to cognitive processes. In contrast, others focus on external or emotional stimuli. Furthermore, specific stimuli are also sensitized. For example, a sleeping mother may be awakened by any movement of her baby, whereas she may not respond to a passing truck.
Function and tasks
The term thalamus comes from the Greek. Translated, it means “sleeping chamber” or “chamber.” However, these terms do not have much to do with the functions of the diencephalic area. The thalamus is a filter that is connected upstream of the cerebral cortex. All information that arrives in this area is preprocessed before being passed on to the cerebrum. Thus, it is up to the thalamus to decide which incoming information is of importance to the body. For this purpose, the afferent (feeding) neurons transmit information from the organism to the thalamus. There, switching to subsequent neurons occurs in the specific thalamic nuclei, resulting in transmission to the cerebrum. The switching takes place through a simple processing of the information, whereby the thalamus acts as a filter and separates unimportant information from important data. The non-specific thalamic nuclei are responsible for controlling this function. These receive their input from other areas of the brain.In this way, the thalamus’ decisions about important information are tuned within the context of the overall physical situation.
Diseases and ailments
Pathological damage to the thalamus can have a significant impact on the organism. The lesions primarily affect the opposite (contralateral) side of the body. As a result, ataxia often occurs, which is a disorder of movement coordination. Ataxia can occur even with normal muscle strength. Another disorder is hemiparesis. This refers to the incomplete paralysis of one side of the body, such as hemiplegia. Among the most common causes of hemiparesis is stroke. Another possible consequence of thalamic damage is thalamic pain, also called central pain. Thus, lesions of the thalamus often result in lesions in other areas of the central nervous system (CNS), again resulting in pseudothalamic pain. If the nucleus ventralis posterolateralis is affected, this leads to disturbances in depth and surface sensibility. The disturbance becomes noticeable by a feeling of heaviness in the limbs. However, large-scale damage to the thalamus occurs only in rare cases. However, when they do occur, affected individuals suffer sensory and motor deficits. In addition, psychological problems occur. Other conceivable consequences due to damage to the thalamus include impaired attention, sensory disturbances, personality changes, and clouding of consciousness.
