Thalamus

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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The thalamus is a core area of ​​the diencephalon. It is the collection point for all sensory impressions with the exception of the sense of smell, which are switched here on the way to the cerebral cortex - i.e. all impressions of seeing, hearing, feeling and the sensation of temperature and pain. The thalamus is therefore also known as the “gateway to consciousness”. Read everything you need to know about the thalamus: function, anatomy and important disorders!

What is the thalamus?

The thalamus forms the posterior surface of the diencephalon. It consists of gray and white matter, whereby the gray matter is divided into numerous nuclei (collections of nerve cell bodies) - the thalamic nuclei - by thin sheets of white matter.

The thalamus has an anterior pole towards the caudate nucleus (one of the basal ganglia), in which the anterior main nucleus of the thalamus (nucleus anterior thalami) lies. The rear pole points back and down and forms the cushion (pulvinar thalami). To the side of the pulvinar is an elevation, Corpus geniculatum laterale (the lateral knee hump), and below the front edge of the Corpus geniculatum mediale (the middle knee hump).

The lateral surfaces of the thalamus border the internal capsule. This is the inner capsule of the brain, an area of ​​white matter where projection fibers ascend and descend from the cerebral cortex to the bridge, medulla oblongata, and spinal cord. The front surface is fused with the hypothalamus.

The thalamus has thalamus radiation (Radiationes thalamicae) radiating to the side and front. This is also called the wreath of the thalamus and consists of double-stranded fiber strands by which the thalamus is connected to the cerebral cortex.

What is the function of the thalamus?

The thalamus is the gateway to consciousness. It acts as a filter and distributor of the incoming information. Here it is decided which sensory impressions from the environment and the organism should penetrate into consciousness and which are then passed on to the corresponding processing centers. All sensory impressions of feeling, seeing and hearing - but not of smelling - are conveyed via the thalamus.

The thalamic nuclei in turn house smaller nuclei and areas with different functions. In the middle and rear core groups of the thalamic nuclei, all somatosensitive and sensory pathways (with the exception of the olfactory pathways) that come from the periphery and extend to the cerebral cortex are switched over. All connections are double-tracked with the corresponding bark fields. This makes it possible through concentrated attention to perceive different sensory impressions to different degrees: strong, low or almost nonexistent.

Visual and auditory impressions are switched in the nuclei of the metathalamus (corpus geniculatum laterale and mediale) on their way to the visual and auditory cortex.

The anterior core groups of the thalamic nuclei are not excited via the periphery (as in the middle and posterior ones), but via the pallidum (a basal ganglion), the cerebellum and the midbrain. These thalamic nuclei are connected to the motor and premotor cortex and can influence movement sequences.

Affective and instinctual excitations, emotional sensations are switched in the thalamic nuclei and passed on to the associated cortical areas.

Taste information is brought together via the taste core and passed on to the taste cortex via the thalamus.

Where is the thalamus located?

The thalamus is located in the diencephalon, which is connected to the brain stem. Its core mass lies on both sides of the third cerebral ventricle and is covered by the two cerebral hemispheres.

What problems can the thalamus cause?

The so-called thalamus syndrome (Déjerine-Roussy syndrome) occurs when a blood clot blocks an important vessel in the thalamus (such as the thalamostriate artery) (thrombosis). The consequence is a failure of the thalamus with visual and sensory disturbances, hemianopsia (half-sided blindness), a strong excitability of the reflexes as well as a reduced sensitivity of the skin and a disturbance of the deep sensitivity.

In general, sensitive disorders with reduced sensitivity, hypersensitivity to all sensory stimuli (with an increased stimulus threshold, however), sensory disorders and severe central pain in the side opposite the disorder indicate disorders in this brain region. Motor disorders with rigid facial muscles and hyperkinesia (forced movements of the hands and fingers) and psychological disorders with reduced alertness, irritability, impatience and nervousness can also indicate damage or illness in the thalamus.

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